NCICT Project of NAITA
Transcript of NCICT Project of NAITA
ACKNOWLEDGEMENTSACKNOWLEDGEMENTSACKNOWLEDGEMENTSACKNOWLEDGEMENTS
I have grate pleasure in expressing my heartiest thanks to the who have
helped me submit this project first and fore most I would like
acknowledgements with pleasure Mr.S.Seelan, Computer Co-ordinator and
lecture in NAITA. I am grateful to Mr.S.Pavalanathan, present NAITA
chairmen who also help me.
I have to also personally thankful to Mr.S.Seelan, lecture NAITA
Computer Training Center and supervisor for this project report for valuable
ideas, recommendations and supports, he whice have added quality to this
project.
I am also especially thank our public library in Vavuniya and I take this
opportunity offering my grateful thank to all my friends and colleagues and my
family members who have been grate help to me personally prepare this
project.
Once again I thank to you all.
............................................
(A.KOGULAN)
CONTENTSCONTENTSCONTENTSCONTENTS
Chapters Page
Chapter 01
Introduction to computer 001
What is Information Technology? 002
Father of computer 004
Computer or a pc 005
Computers in human lives 007
A complete computer system 009
Age of computers 010
Classification of Computers 012
The Five Generations of Computers 018
Computer Generations briefly Explanation 021
Artificial intelligence 029
Main Circuit Board of a PC 030
History of the Motherboard 036
Programming Languages 040
Intel Processors: Now and Then 044
Chapter 02
The Components of a Computer 053
Input Devices 058
Output Devices 069
CPU (Central Processing Unit) 076
How computers work? 079
Booting Process 080
Operating system 082
Chapter 03
System Software 090
Application Software 095
Chapter 04
Introduction to Computer Viruses 099
Installing Anti-virus Software 110
Chapter 05
Primary Storage 122
Secondary Storage 128
Chapter 06
Networks 137
Internet & WWW 172
The Number Systems 217
Characters and decimal, binary, ASCII, EBCDIC Value
Capital Letters 220
Small Letters 221
Shortcut Keys 222
What is DOS? 226
DOS commands and explanation 228
Modem error messages 232
Abbreviation 240
INTRODUCTION TO COMPUTERINTRODUCTION TO COMPUTERINTRODUCTION TO COMPUTERINTRODUCTION TO COMPUTER
We might be aware of the fact that the computer is affecting our lives in
many ways. Almost everyday we hear about the newest ways that a computer is
being used for. So why not to Call it a Computer Revolution. Computers have
now become an important part of our lives with all these rapid development
taking place.
Till now you might have been using a typewriter for drafting your
commercial correspondence a calculator for performing lengthy calculations
and files for maintaining records. Now we can do all our correspondence,
calculation and record main fence on a computer at a much faster speed.
Besides facilitating the office work. Computers today are also paying a
significant role in the fields of education and entertainment. As the use of
computers steadily increases, so does the need for batter understanding of its
functions.
WHAT IS INFORMATION TECHNOLOGY?WHAT IS INFORMATION TECHNOLOGY?WHAT IS INFORMATION TECHNOLOGY?WHAT IS INFORMATION TECHNOLOGY?
IT (information technology) is a term that encompasses all forms of
technology used to create, store, exchange, and use information in its various
forms (business data, voice conversations, still images, motion pictures,
multimedia presentations, and other forms, including those not yet conceived).
It's a convenient term for including both telephony and computer technology in
the same word. It is the technology that is driving what has often been called
"the information revolution."
Data and Information
Data is a collection of raw unprocessed facts, figures, and symbols.
Computers process data to create information. Information is data that is
organized, meaningful, and useful. Computer processes several data items to
produce a paycheck. Another example of information is a grade report, which
is generated from data items such as a student name, course names, and course
grades.
A user is someone who communicates with a computer or uses the
information it generates.
Hardware is the electric, electronic, and mechanical equipment that
makes up a computer. Software is the series of instructions that tells the
hardware how to per form tasks. Without software, most hardware is useless.
The hardware needs instructions from software to process data into
information.
Data
(1) In computing, data is information that has been translated into a form
that is more convenient to move or process. Relative to today's computers and
transmission media, data is information converted into binary digital form.
(2) In computer component interconnection and network
communication, data is often distinguished from "control information,"
"control bits," and similar terms to identify the main content of a transmission
unit.
(3) In telecommunications, data sometimes means digital-encoded
information to distinguish it from analog-encoded information such as
conventional telephone voice calls. In general, "analog" or voice transmission
requires a dedicated continual connection for the duration of a related series of
transmissions. Data transmission can often be sent with intermittent
connections in packets that arrive in piecemeal fashion.
(4) Generally and in science, data is a gathered body of facts. Some
authorities and publishers, cognizant of the word's Latin origin and as the plural
form of "datum," use plural verb forms with "data". Others take the view that
since "datum" is rarely used, it is more natural to treat "data" as a singular
form.
Information
Information is stimuli that have meaning in some context for its
receiver. When information is entered into and stored in a computer, it is
generally referred to as data. After processing (such as formatting and
printing), output data can again be perceived as information. Data will be
converted in to Information after processing.
When information is packaged or used for understanding or doing
something, it is known as knowledge.
FAFAFAFATHER OF COMPUTERTHER OF COMPUTERTHER OF COMPUTERTHER OF COMPUTER
Charles Babbage was intrigued by the problem of errors in the hand
calculation of complex mathematical tables. He was inspired by Charles
Mohan’s logic machine which he used as a starting point
and a working difference engine was completed in1822
and was used to calculate simple tables in 1833
Babbage abandoned the project and began
work on his real dream, the “Analytical
Engine”, a general purpose machine that
would be capable of performing any type of
digital calculation. Although his analytical
engine was never built Babbage did succeed in
mapping out all the principles and procedures from which all
modern digital computers have followed. As a result he is considered to be the
source of the automatic computer.
COMPUTER OR A PCCOMPUTER OR A PCCOMPUTER OR A PCCOMPUTER OR A PC
For layman, a PC or a Computer is like a super calculator with a really
big display computer is perhaps the most useful tool ever invented. In technical
terms, computer can be defined as an electronic device that accepts data,
processes information in a pre – defined Fashion, according to the set of
instructions provided to it and produces the desired output.
The term PC, it is self explanatory. PC stands for Personal Computer as
it is your own computer you are working upon. This term was adopted by IBM,
the largest manufacturer of computer, to describe its first desk sized computers.
Computers differ in variety and size – from a simple playing computer
like spectrum to large mainframe or super computer like India’s own super
computer frame.
You might be wondering if a computer can store a large amount of data,
then it must have a huge amount of intelligence too. Ironically, the computer’s
intelligence level does not equal to that of a cockroach even. Through, research
is on to impart some intelligence to if of its own. The computer only follows
the instructions given to it by the user. If follows the concept of what you give
is what you get, which means that whatever instructions you give, accordingly
would be the result. A computer Fed with wrong instructions would give you
wrong results.
Super Computer
COMPUTERS IN HUMAN LIVESCOMPUTERS IN HUMAN LIVESCOMPUTERS IN HUMAN LIVESCOMPUTERS IN HUMAN LIVES
The number of ways that computers affect human lives is uncountable.
Computers can perform all those functions that a human being can do to a
certain extent, but at a much faster speed and with greater accuracy.
Computers are used in banks to take care of the accounting system and
keep track of the enormous amount of money. Although all these tasks are done
manually also, but it takes as great deal of time. If it takes about a month to
make the balance sheet, a computer can make it in a few hours. Computers help
you perform tasks like account handling; taking out complex reports, balance
sheets, etc in a much shorten span and the results would also be very accurate.
Let us take an example that you have an account in a bank which is fully
computerized throughout the country. You leave an account in one of its
branch in Colombo but at present you are in Vavuniya and you wish to encase
a cheque. You need not call up Colombo branch, and confirm your account and
perform other formalities. The cashier at Vavuniya branch of the bank would
check up your bank account number of Colombo on computer and if it is there
and you have the essential amount of money in your account, your cheque will
immediately get encased see how simple it is with a computerized system!
Now let us take up an example of an architect who designs your houses
and buildings. Suppose he has been asked to design a housing complex with
each lat of about 2000 sq.ft. According to the dimensions of the area and the
number of houses required, he would draw the design or layout of that
complex, which could take about a month or so. Let us suppose, he completes
the project and is given another assignment for another housing complex, but
with a greater area of say 2500 sq.ft. Now if the architect starts off with the
drawing it right. From the beginning it would take another month or so. Don’t
you think it consumes too much time? There is a possibility that he could
commit some mistakes which will head to redoing of the same job. A computer
can provide a great deal of help in this context also If you have a certain
program in your computer that could help you draw the layout according to the
dimensions and many other things you specify the time of drawing could be
reduced to a few hours or even less. More over, if you get a new assignment to
draw the same design with a greater area, you would be able to finish it in
relatively no time, if you have saved the previous assignment, in the computer.
So a computer makes the job much simpler and easier and most of all, the least
time consuming.
These examples are just a fraction of the world-wide trend about the
various jobs that a computer can perform computers are used broadly even in
educational institutions, by doctors, in business for guiding astronauts through
space and much more. We have developed a society that is almost dependent
on computerized system of functioning. So it becomes very essential to have
the basic knowledge of the computer system.
A A A A COMPLETE COMPUTER SYSTEMCOMPLETE COMPUTER SYSTEMCOMPLETE COMPUTER SYSTEMCOMPLETE COMPUTER SYSTEM
The computer system comprises of Hard Ware, Soft Ware, Live Ware and Firm
Ware.
Hard Ware
All the tangible devices which are uses in computerize systems.
Soft Ware
These are the program devices the hard ware and perform different task.
These including operating system like DOS, Productively soft ware like
spooling.
Live Ware
The human involvement for the computer systems. A computer system
like information systems managers, system analysts, programmers etc.
Firm Ware
Firmware is a big program
E.g.:- Boot Strap Program
Total computer systems.
Hard Ware Soft Ware Live Ware Firm Ware
AGE OF COMPUTERSAGE OF COMPUTERSAGE OF COMPUTERSAGE OF COMPUTERS
1946 J.Presper Eckert, John Manchely and a team of so complete the
electronic numerical intergrator and computer (ENIAC). The first large
– scale electronic digital computer weights 50 tons, stands two stories,
and covers 15000 square feet.
1947 Grace Hopper documents the first computer bug, a tread moth in a
cabinet of the Mark II.
1949 Mource Wilkes of England’s Cambridge University builds the first
stored – program Computer.
1950 The first computer of use binary or digital mathematics. [EDVAC]
1951 The University Automatic computer. The first American commercially
Produced this computer.
1953 IBM introduces the first magnetic tape device. The model 726.
1956 The term “Artificial Intelligence” is corned by MC curtly.
1959 Commercial and Business oriented language (COBOL) is created.
1960 The first modern computer generation ends as vacuum tubes punched
cards and machine code give way to 2nd generation transistors magnetic
tape and languages in computer design and operation.
1965 The 3rd generation is developing by tom Kurtz and John Kemeny of
Dortmaith Collage.
1967 The 3rd generation is under way with IC.
1969 The Intel 4004 becomes the first micro processor and paves the way for
the micro computer.
1975 The Cray 1 super computer is introduced as the fastest computer on
earth.
1977 Introduces the Apple II Personal Computer.
1978 VisiCalc, Electronic spread sheet software is created by Don Brick in.
1979 Micro International releases word start a word processing program.
1981 The IBM PC debuts Microsoft’s MS – DOS becomes its standard
operating software.
1983 Lotus 123 takes VisiCalc’s place as the leading spread sheet program
marketed by company founder, Mitch Kaptur windows is presented by
Microsoft.
1985 The C++ programming language is developed.
1990 The advent of parallel processing and greatly increased processing
power make this the year of Artificial Intelligence.
1992 Apples announce “Personal Digital Assistant”.
1993 Intel PC chips; Pentium developed.
2000 Experts predict that computers containing a billion processors will be
technology feasible exceeding the power of the human brain.
CLASSIFICATION OF COMPUTERSCLASSIFICATION OF COMPUTERSCLASSIFICATION OF COMPUTERSCLASSIFICATION OF COMPUTERS
Classification of Computers we can basically divide in to 3 sections. Based on
generation, size and data representation.
Generations: 1 to 5
Generation & Time Period
First Generation 1946 — 1956
Use of vacuum tubes, large, limited memory, jobs execution coordinated
manually, and speed up to 10,000 ips.
Second Generation 1957— 1963
Use of transistors, more reliable, less heat generation, less power requirement,
speed 200,000 - 300,000 ips.
Third Generation 1964 — 1979
• Use of Integrated Circuits (ICS) by printing hundreds and thousands of tiny
transistors on to small silicon chips
• Speed up to 5 Million Instructions Per Second (MIPS)
• Use of operating systems that automated the running of programs &
communications between CPU & peripheral devices.
• Availability of hardware independent programming.
Fourth Generation 1980s
Use of LS1 & VLSI circuits, costs fallen to a very low level, large memory &
storage, speed up to 200 MIPS
Fifth Generation
5 generation computers will be Artificial Intelligence Systems called Al
computers, which simulate the human brain. Expert systems also fall into this
category.
Size: Micro, Mini, Mainframe, Super
Micro Computers
A microcomputer is a complete computer on a smaller scale and is generally a
synonym for the more common term, personal computer or PC, a computer
designed for an individual. A microcomputer contains a microprocessor (a
central processing unit on a microchip), memory in the form of read-only
memory and random access memory, I/O ports and a bus or system of
interconnecting wires, housed in a unit that is usually called a motherboard.
In an ascending hierarchy of general computer sizes, we find:
• An embedded systems programming computer, which is embedded in
something and doesn't support direct human interaction but nevertheless
meets all the other criteria of a microcomputer
• Microcomputer
• Workstation, as used to mean a more powerful personal computer for
special applications
• Minicomputer, now restyled a "mid-range server"
• Mainframe or mainframe computer, which is now usually referred to by its
manufacturers as a "large server"
• Supercomputer, formerly almost a synonym for "Cray supercomputer" but
now meaning a very large server and sometimes including a system of
computers using parallel processing
• A parallel processing system is a system of interconnected computers that
work on the same application together, sharing tasks that can be performed
concurrently
Mini Computers
A minicomputer, a term no longer much used, is a computer of a size
intermediate between a microcomputer and a mainframe. Typically,
minicomputers have been stand-alone computers (computer systems with
attached terminals and other devices) sold to small and mid-size businesses for
general business applications and to large enterprises for department-level
operations. In recent years, the minicomputer has evolved into the "mid-range
server" and is part of a network. IBM's AS/400e is a good example.
Mainframes
Mainframe is an industry term for a large computer, typically manufactured by
a large company such as IBM for the commercial applications of Fortune 1000
businesses and other large-scale computing purposes. Historically, a mainframe
is associated with centralized rather than distributed computing. Today, IBM
refers to its larger processors as large servers and emphasizes that they can be
used to serve distributed users and smaller servers in a computing network.
Super Computers
A supercomputer is a computer that performs at or near the currently highest
operational rate for computers. A supercomputer is typically used for scientific
and engineering applications that must handle very large databases or do a
great amount of computation (or both). At any given time, there are usually a
few well-publicized supercomputers that operate at the very latest and always
incredible speeds. The term is also sometimes applied to far slower (but still
impressively fast) computers.
Most supercomputers are really multiple computers that perform parallel
processing.
In general, there are two parallel processing approaches: symmetric
multiprocessing (SMP) and massively parallel processing (MPP).
Perhaps the best-known builder of supercomputers has been Cray Research,
now a part of Silicon Graphics. Some supercomputers are at "supercomputer
center," usually university research centers, some of which, in the United
States, are interconnected on an Internet backbone known as vBNS or NSFNet.
This network is the foundation for an evolving network infrastructure known as
the National Technology Grid. Internet2 is a university-led project that is part
of this initiative.
At the high end of supercomputing are computers like IBM's "Blue Pacific,"
announced on October 29, 1998. Built in partnership with Lawrence Livermore
National Laboratory in California. Blue Pacific is reported to operated at 3.9
teraflop (trillion operations per second), 15,000 times faster than the average
personal computer. It consists of 5,800 processors containing a total of 2.6
trillion bytes of memory and interconnected with five miles of cable. It was
built to simulate the physics of a nuclear explosion. IBM is also building an
academic supercomputer for the San Diego Supercomputer Center that will
operate at 1 teraflop. It's based on IBM's RISC System/6000 and the AIX
operating system and will have 1,000 microprocessors with IBM's own
POWER3 chip.
At the lower end of supercomputing, a new trend, called clustering, suggests
more of a build-it-yourself approach to supercomputing. The Beowulf Project
offers guidance on how to "strap together" a number of off-the-shelf personal
computer processors, using Linux operating systems, and interconnecting the
processors with Fast Ethernet. Applications must be written to manage the
parallel processing.
Data Representation: Analog, Digital, Hybrid.
Analog Computer
An analog computer operates in a completely opposite way to the digital
computer.
For a start, all operations in an analog computer are performed in parallel.
Secondly, data are represented in an analog computer as voltages, a very
compact but not necessarily robust form of storage (prone to noise corruption).
A single capacitor (equivalent to the Digital’s computer use of a transistor) in
an analog computer can represent one continuous variable.
The Heath kit Educational Analog Computer is completely self-contained and
contains nine DC operational amplifiers with provision for balancing without
removing problem setup. It also features three initial condition power supplies,
five coefficient potentiometers, four sets of relay contacts, an electronically
regulated power supply and a built-in repetitive oscillator for automatic
operation. The complete EC-1 kit also contains an assortment of precision
resistors, capacitors, special silicon diodes and patch cords for setting up scores
of complex computer problems easily and accurately.
Digital Computer
The digital computer is a sequential device, in general, operating on data one
step at a time; in addition the digital computer represents data internally using a
quite verbose but very robust form of representation called binary. Thus a
single transistor in a digital computer can only store two states, on and off.
Obviously to store a number to any sensible degree of precision, many
transistors are required.
Hybrid Computer
A computer that processes both analog and digital data.
A Hybrid Computer is a combination of computers that are capable of inputting
and outputting in both digital and analog signals. A hybrid computer system
setup offers a cost effective method of performing complex simulations.
Purpose: Special, General
Depending on the purpose we can categorize the computers mainly on to two.
Special Purpose Computers
Special Purpose Computers are used for special purposes like scientific
researches, atomic weapon researches, designing sophisticated vehicles,
weather forecasting etc.
Normally super computers come under special purpose computers as we
discussed earlier.
General Purpose Computers
General Purpose Computers are the normal computers we are using.
THE FIVE GENERATIONS OF COMPUTERSTHE FIVE GENERATIONS OF COMPUTERSTHE FIVE GENERATIONS OF COMPUTERSTHE FIVE GENERATIONS OF COMPUTERS
The history of computer development is often referred to in reference to
the different generations of computing devices. Each generation of computer is
characterized by a major technological development that fundamentally
changed the way computers operate, resulting in increasingly smaller, cheaper,
and more powerful and more efficient and reliable devices. Read about each
generation and the developments that led to the current devices that we use
today.
First Generation - 1940-1956: Vacuum Tubes
The first computers used vacuum tubes for circuitry and magnetic drums
for memory, and were often enormous, taking up entire rooms. They were very
expensive to operate and in addition to using a great deal of electricity,
generated a lot of heat, which was often the cause of malfunctions. First
generation computers relied on machine language to perform operations, and
they could only solve one problem at a time. Input was based on punched cards
and paper tape, and output was displayed on printouts.
The UNIVAC and ENIAC computers are examples of first-generation
computing devices. The UNIVAC was the first commercial computer delivered
to a business client, the U.S. Census Bureau in 1951.
Second Generation - 1956-1963: Transistors
Transistors replaced vacuum tubes and ushered in the second generation
of computers. The transistor was invented in 1947 but did not see widespread
use in computers until the late 50s. The transistor was far superior to the
vacuum tube, allowing computers to become smaller, faster, cheaper, more
energy-efficient and more reliable than their first-generation predecessors.
Though the transistor still generated a great deal of heat that subjected the
computer to damage, it was a vast improvement over the vacuum tube. Second-
generation computers still relied on punched cards for input and printouts for
output.
Second-generation computers moved from cryptic binary machine
language to symbolic, or assembly, languages, which allowed programmers to
specify instructions in words. High-level programming languages were also
being developed at this time, such as early versions of COBOL and
FORTRAN. These were also the first computers that stored their instructions in
their memory, which moved from a magnetic drum to magnetic core
technology. The first computers of this generation were developed for the
atomic energy industry.
Third Generation - 1964-1971: Integrated Circuits
The development of the integrated circuit was the hallmark of the third
generation of computers. Transistors were miniaturized and placed on silicon
chips, called semiconductors, which drastically increased the speed and
efficiency of computers.
Instead of punched cards and printouts, users interacted with third
generation computers through keyboards and monitors and interfaced with an
operating system, which allowed the device to run many different applications
at one time with a central program that monitored the memory. Computers for
the first time became accessible to a mass audience because they were smaller
and cheaper than their predecessors.
Fourth Generation - 1971-Present: Microprocessors
The microprocessor brought the fourth generation of computers, as
thousands of integrated circuits were built onto a single silicon chip. What in
the first generation filled an entire room could now fit in the palm of the hand.
The Intel 4004 chip, developed in 1971, located all the components of the
computer - from the central processing unit and memory to input/output
controls - on a single chip.
In 1981 IBM introduced its first computer for the home user, and in
1984 Apple introduced the Macintosh. Microprocessors also moved out of the
realm of desktop computers and into many areas of life as more and more
everyday products began to use microprocessors.
As these small computers became more powerful, they could be linked
together to form networks, which eventually led to the development of the
Internet. Fourth generation computers also saw the development of GUIs, the
mouse and handheld devices.
Fifth Generation - Present and Beyond: Artificial
Intelligence
Fifth generation computing devices, based on artificial intelligence, are
still in development, though there are some applications, such as voice
recognition, that are being used today. The use of parallel processing and
superconductors is helping to make artificial intelligence a reality. Quantum
computation and molecular and nanotechnology will radically change the face
of computers in years to come. The goal of fifth-generation computing is to
develop devices that respond to natural language input and are capable of
learning and self-organization.
COMPUTER GENERATIONSCOMPUTER GENERATIONSCOMPUTER GENERATIONSCOMPUTER GENERATIONS BRIEFLY BRIEFLY BRIEFLY BRIEFLY
EXPLANATIONEXPLANATIONEXPLANATIONEXPLANATION
First Generation [1946 – 1955]
We have just read about the first generation of computer. These
computers used value (vacuum tube) technology and had the main limitations
of very large electric power consumption and very little reliability.
In 1946, Eckert and Mouchley formed their company the UNIVAC
divitision of Remington Rand, Inc. This company made the first commercial
computer UNIVAC division in 1951. The UNIVAC had a memory capacity of
1000 words. It used magnetic tapes as input or output devices. It has used to
predict the election of Dwlight D.Eisen howen (one of the president of USA) in
1952.
A similar computer whirlwind one was built in 1951 by the
Massachusetts Institute of Technology, USA. It had a memory capacity of 2048
word.
In 1953 IBM installed its first computer the IBM 701 late in 1954 the
IBM developed a general purpose computer. IBM 650 computer was the most
popular one during that time. To over come the small storage capacity of IBM
650 and to produce a more efficient system the IBM developed IBM – 1401
add RAMAC 350.
The first generation computers were characterized by electronic tube
circuitry. Hence they were very large air – conditioned room. They had small
internal storage and were relatively showed. The First generation machines
used punched paper tape, punched card, magnetic wire, magnetic tape and
printers as input or output devices.
Second Generation [1957 – 1963]
With the advent of transition technology, a second generation of
computer comes into existence. These computers were smaller in size, more
reliable and highly efficient. These machines used English like language know
as High Level Language (HLL) for ease of operation and application in
business and scientific analysis many American and European companies
manufactured these machines. One of them the IBM – 1401 was the most
popular and some of the IBM – Organization use this model even today.
These computers were called the generations of computer. They have
faster access and were more reliable than the first generation of computer.
They were characterized by both vacuum tube (value) and discrete
transistor logic. By this time a wider range of input or output devices such as
higher performance magnetic tapes, magnetic drums and early
magnetic disks were available during the second generation
computer language such as FORTRAN and ALGOL were
introduced. The picture of a second generation
computer IBM – 7070 is shown below. The second generation of
computers started with the introduction of transistorized computer. The first of
these, the IBM 7090 was delivered in 11959 which were followed by the CDC
1604, The Phil co 2000 and Remington rondo’s UNIVAC, LARC.
Other widely used second generations of computer were
• IBM 1620
• IBM 1401
• IBM 7094
Third Generation [1964 – 1979]
In the sixtieth Integrated Circuits (IC) popularly know as ICs came in
the field of micro – electronics computers, that use a large junk of electronic
components were substantially benefited both from the point
of price reduction as well as size reduction these
machines consumed very little power and
were highly reliable.
These machines used more versa tike
programs like real time operation system,
multiprogramming, techniques and data base management, IBM – 370,
some of the most popular machine of this generation. Many others models are
given in table.
Manufacturer Model
Moore school of Electrical
Engineering
ENIVAC, EDVAC
Cambridge University EDSAC
Univas Univac I, Univac II
Burroughs E101, Burroughs 2022
Honey Well Data matic 1000
IBM Mark II, Mark III, 604 electronic
punch, calculating
IBM 650
IBM 702
IBM 704
IBM 705
IBM 709
National cash Register CRC, 1024, 102D
RC4 BIZMAC I, BIZMAC II
In the third generation computers more than were user could work with
the computer at the same time, where as first and second generation of
computers worked on a one – to – one basis.
Almost all computers introduced after 1966 were said to be third
generation computer. Most of the main frame computers use till the early
1980’s were third generation computers only a good.
Fourth Generation [1980 – Present]
Forth generation of computers were produced after 1980 the fourth
generation computer is used to designate micro computers which use large
scale integrated circuits (LSI) and very large scale integrated circuits (VLSI) in
the memory unit.
The invention of micro process or chip has created a revolution in the
reduction of price and size of this generation machines. These machines have
followed advantages over other generation.
1. These computers use advanced techniques to feed.
2. Data into them and to bring out processed data for use of the outside world.
Then can even be connected with the satellite communication links to trans
form information from one hart of the world at very high speed. These
Machines use advance application.
3. These machines use advance software such as process controverts,
computer aided design (CAD), electronic spread sheet (Lotus 123) and data
base management. Because of this these machines of table size type writer
have the same power which was available in very large computers of the
third generation.
Fifth Generation [Future]
We are presently straddling for the line between fourth and fifth
generation computers. In 1981 a group of Japanese design and build the fifth
generation machines this consortium believed generation machines. This
consortium believed it was possible for such a machine to per for the following.
� Accept Spoken instructions and such graphic images as photographs as
data input.
� Collect select and store useful data form newspapers, books tape
recorded speeches and other common sources.
� Translate foreign languages research and provide answers to questions
by using all available data.
� Learn from its own experiences program itself.
The US computer industry was at a dosed vantage in early phases of the
fifth generation race because antitrust laws restricted. The ability of companies
to co-operate by comparison the Japanese government brought together all of
its resources and all companies with in its electro nice industry for a coopered
fives concerted effort since these early days the government in the United
States has sanctioned special research and development cooperatives formed by
a number of computer companies induction some of the largest companies part
equally IBM hare established special developmental efforts budgets for
advanced computing capabilities. The fifth generation of computers is seen as
having increased processing capabilities, data handling and storage facilities
software will respond to the natural language of people.
The new technologies discussed below are seen as heys to implementing
fifth generation systems.
Optics and super conductive materials
� Parallel Processing
� Artificial Intelligence (AI)
� Language translation and non traditional input
� Special purpose machines
ARTIFICIAL INTELLIGENCEARTIFICIAL INTELLIGENCEARTIFICIAL INTELLIGENCEARTIFICIAL INTELLIGENCE
Computers are starting to simulate human thought and argument one
type of software application is known as Artificial Intelligence (AI). This
growing one of development scythe sizes computer science psychology
linguistics and other specialized fields to perform tasks with human live logic.
Among 5th AI developments expected in fifth generation computers are
heuristic problem solving techniques. The term heuristic describes are solved
through application of general rules and information based on experience.
Instead of following precise sequence of instructions to devices solutions
heuristic software applies rules proven to be effective in the past as example
heuristic techniques are used to develop programs that play chess vast human
of moves are possible in a same of chess with heuristic capabilities the
computer as able to evaluate different moves to bulls a games strategy thus.
The chess playing computer able to respond to variable situation is several
different ways computers scientists around the world are building system that
can learn form experience and are able to apply this in for motion to new
situations.
MAIN CIRCUIT BOARD OF A PCMAIN CIRCUIT BOARD OF A PCMAIN CIRCUIT BOARD OF A PCMAIN CIRCUIT BOARD OF A PC
A motherboard is the physical arrangement in a computer that contains
the computer's basic circuitry and components. On the typical motherboard, the
circuitry is imprinted or affixed to the surface of a firm planar surface and
usually manufactured in a single step. The most common motherboard design
in desktop computers today is the AT, based on the IBM AT motherboard. A
more recent motherboard specification, ATX, improves on the AT design. In
both the AT and ATX designs, the computer components included in the
motherboard are:
• The microprocessor
• (Optionally) coprocessors
• Memory
• Basic input/output system (BIOS)
• Expansion slot
• Interconnecting circuitry
Additional components can be added to a motherboard through its
expansion slot. The electronic interface between the motherboard and the
smaller boards or cards in the expansion slots is called the bus.
Bus
In a computer or on a network, a bus is a transmission path on which
signals are dropped off or picked up at every device attached to the line. Only
devices addressed by the signals pay attention to them; the others discard the
signals. According to Winn L. Rosch, the term derives from its similarity to
autobuses that stop at every town or block to drop off or take on riders
In general, the term is used in two somewhat different contexts:
(1) A bus is a network topology or circuit arrangement in which all
devices are attached to a line directly and all signals pass through each of the
devices. Each device has a unique identity and can recognize those signals
intended for it.
(2) In a computer, a bus is the data path on the computer's motherboard
that interconnects the microprocessor with attachments to the motherboard in
expansion slots (such as hard disk drives, CD-ROM drives, and graphics
adapters).
Chips
Chip" is short for microchip, the incredibly complex yet tiny modules
that store computer memory or provide logic circuitry for microprocessors.
Perhaps the best known chips are the Pentium microprocessors from Intel. The
PowerPC microprocessor, developed by Apple, Motorola, and IBM, is used in
Macintosh personal computers and some workstations. AMD and Cyrix also
make popular microprocessor chips.
There are quite a few manufacturers of memory chips. Many special-
purpose chips, known as application-specific integrated circuits, are being
made today for automobiles, home appliances, telephones, and other devices.
A chip is manufactured from a silicon (or, in some special cases, a
sapphire) wafer, which is first cut to size and then etched with circuits and
electronic devices. The electronic devices use complementary metal-oxide
semiconductor technology. The current stage of micro-integration is known as
Very Large-Scale Integration (VLSI). A chip is also sometimes called an IC or
integrated circuit.
Ports
On computer and telecommunication devices, a port (noun) is generally
a specific place for being physically connected to some other device, usually
with a socket and plug of some kind. Typically, a personal computer is
provided with one or more serial ports and usually one parallel port. The serial
port supports sequential, one bit-at a-time transmission to peripheral devices
such as scanners and the parallel port supports multiple-bit-at-a-time
transmission to devices such as printers.
Expansion Slots
In computers, a slot, or expansion slot, is an engineered technique for
adding capability to a computer in the form of connection pinholes (typically,
in the range of 16 to 64 closely-spaced holes) and a place to fit an expansion
card containing the circuitry that provides some specialized capability, such as
video acceleration, sound, or disk drive control.
Almost all desktop computers come with a set of expansion slots. These
help ensure that you'll be able to add new hardware capabilities in the future.
SIMM
A SIMM (single in-line memory module) is a module containing one or
several random access memory (RAM) chips on a small circuit board with Pins
that connect to the computer motherboard. Since the more RAM your computer
has, the less frequently it will need to access your secondary storage (for
example, hard disk or CD-ROM); PC owners sometimes expand RAM by
installing additional SIMMs. SIMMs typically come with a 32 data bit (36 bits
counting parity bits) path to the computer that requires a 72-pin connector.
SIMMs usually come in memory chip multiples of four megabytes.
The memory chips on a SIMM are typically dynamic RAM (DRAM)
chips. An improved form of RAM called Synchronous DRAM (SDRAM) can
also be used. Since SDRAM provides a 64 data bit path, it requires at least two
SIMMs or a dual in-line memory module (DIMM).
RIMM
In a computer, a RIMM is a memory module developed by Kingston
Technology Corp. that takes up less space inside the computer than the older
DIMM module and has different PIN characteristics. A RIMM has a 184-pin
connector and an SO-RIMM module has a 160-pin connector. An SO-RIMM is
smaller and is used in systems that require smaller form factors. While RIMM
is commonly believed to stand for "Rambus inline memory module," Kingston
Technology has trademarked "RIMM" and uses only that term.
A RIMM module consists of RDRAM chips that are attached using a
thin layer of solder, a metal alloy that, when melted, fuses metals to each other.
Solder balls on each chip create a metal pathway used to conduct electricity.
DIMM
A DIMM (dual in-line memory module) is a double SIMM (single in-
line memory module). Like a SIMM, it's a module containing one or several
random access memory (RAM) chips on a small circuit board with pins that
connect it to the computer motherboard. A SIMM typically has a 32 data bit
(36 bits counting parity bits) path to the computer that requires a 72-pin
connector. For synchronous dynamic RAM (SDRAM) chips, which have a 64
data bit connection to the computer, SIMMs must be installed in in-line pairs
(since each supports a 32 bit path). A single DIMM can be used instead. A
DIMM has a 168-pin connector and supports 64-bit data transfer. It is
considered likely that future computers will standardize on the DIMM.
VDU Interface
A device used for the real-time temporary display of computer output data.
Note: Monitors usually use cathode-ray-tube or liquid-crystal technology.
Synonyms video display terminal, video display unit, visual display unit.
VDU, or "video terminal", "video display terminal", VDT, "display terminal")
A device incorporating a cathode ray tube (CRT) display, a keyboard and a
serial port. A VDU usually also includes its own display electronics which
store the received data and convert it into electrical waveforms to drive the
CRT.
VDUs fall into two categories: dumb terminals and intelligent terminals
(sometimes called "programmable terminals").
Early VDUs could only display characters in a single preset font, and these
were confined to being layed out in a rectangular grid, reproducing the
functionality of the paper-based teletypes they were designed to replace.
Later models added graphics facilities but were still driven via serial
communications, typically with several VDUs attached to a single multi-user
computer. This contrasts with the much faster single bitmap displays integrated
into most modern single-user personal computers and workstations.
The term "Display Screen Equipment" (DSE) is used almost exclusively in
connection with the health and safety issues concerning VDUs.
HISTORY OF THE MOTHERBOARDHISTORY OF THE MOTHERBOARDHISTORY OF THE MOTHERBOARDHISTORY OF THE MOTHERBOARD
Before starting to look at the motherboard inn detail it is worthwhile
examining the g\history of its development over the years. Motherboards have
changed radically in order to accommodate the latest developments in
technology such as new CPUs, different types of memory, different expansion
buses (and cards), and to some extend to meet the need for smaller system
units.
Looking back, the earliest computers were often produced as kits aims at
hobbyist and electronic enthusiast. With these kits the electrical components
were installed using a commercial board approach with the manually soldered
components. The customer essentially built the computer according to a set of
assembly instructions and standard components.
As computer design and manufacturing technique developed, computers
began to incorporate a separate simple circuit board with a logical layout for
placing the electrical components. This was basically the first motherboard and
led to the development of chip sockets and components pinholes wit an etched
circuit. This enables a production assembly line of workers to manually insert
and solder all discrete parts in place.
With the development of new manufacturing techniques such as wave
soldering and machines for large-scale automation of components installation
quantity and production rates improved. With the rapid development of
manufacturing technique to increase the no\umber of transistors per chip
offered by Large Scale Integration (LSI) and then Very Large Scale Integration
(VLSI), motherboard design has evolved to the point where the number of
physical components required for a system has been reduced dramatically.
When IBM introduced the first popular PC 5150 in 1981, the
motherboard contained a large number of memory chips conventionally taking
up a larger part of the motherboard surface area. Other semiconductors devices
were installed in a simple row format alone with an extends system bus
offering five 8 bit ISA standard expansion card slots.
The physical size of this early motherboard was largely a reflection of
the number of chips supported and design of bus and peripheral ports. The
original motherboard used in the PC 5150 had over 100 Integrated Circuit (IC)
chips and naturally the introduced of LSI and VSLI led to a reduction of the
number of support chips required. This physical size and the layout of major
components are termed as a board from factor and as we shall see later, are
used in identifying difficulty types of motherboard.
The first real standard motherboard was introduced with the IBM PC XT
in 1983. The number of expansion slots was increased from five to eight, with
less space allotted between the slots. This motherboard set a standard for board
design and was taken up by many other PC manufactures in the transition to 16
bit processing; the form factory this board become known as the Baby-AT.
In 1984, IBM brought out a new 16-bit processor PC called the IBM PC
AT. This used a large physical size from factor boars then the Baby At and was
called Full Size AT.
This broad has eight bit slots, with six of those having a slot extension to
support 16 bit PC cards.
Many IBM compatible suppliers incorporating the 16 bit features of the
Full Size AT board manufactured the Baby-AT board. These boards were so
similar that the Baby- AT could easily replace the Full Size AT board as an
upgrade. Both boards initially had a single 5 pin DIN keyboard connectors
mounted on the motherboard with a hole in the computer chassis rear panel to
provide access. The 5-pin DIN keyboard socket on this motherboard was
eventually replaced with a mini-DIN 6-pin PS/2 type keyboard socket before
this motherboard design was eventually superseded.
During 1987 Western Digital created new motherboard from faction
called the LPX and mini-LPX. These boards were fro incorporation slim-line or
low profile computers.
A major difference with this motherboard is that PC expansion cards
cannot be installed vertically because of the limited computer casing height.
Instead these boards have a single system bus slot on the motherboard from
which a special extender card or riser card is mounted at right angles. The riser
card has built-in expansion slot and supports PC expression card mounted
horizontally.
LPX or Mini-LPX from factor motherboards can easily be recognized,
external to a computer by the use of horizontal chassis opening for expanses
slots on desktop or vertical slots when the motherboard is mounted in a tower
computer case. An LPX board has two PS/2 type connectors (one fro the
keyboard and one for a mouse) mounted on the motherboard with two 9 pin
serial sockets and single parallel sockets.
Another from factor motherboard, called the NLX is very similar to the
board to be used in PCs until the mid to late 1990s. By then a new motherboard
from factor called ATX began to replace the Baby-AT.
In 1997 Intel introduced a new motherboard from factor called ATX.
Combining build and components qualities from both the Baby-AT and LPX
boards with new boards design features; this motherboard is the basis for the
current most popular standard.
It is also has the new 20 pin power supply connectors with supplied
+3.3.V for processor supply.
Because of the advances in VLSI motherboard manufactures have been
able to save a considerable amount of space in their designs. This extra many
of the functions, such as video audio and new networking that previously
required additional expansion card.
Just as with the original AT deign many manufacturers have introduced
a compact version of the ATX format motherboard called the Mini ATX. With
the integration of more and more functions onto the motherboard the need for
expansion slots has deceased. Therefore instead of providing seven expansion
slot as with the ATX from factor the Mini ATX motherboard typically has just
three or four factories the Mini means that the Mini ATX motherboard can be
filtered in to cheaper more compact system unit cases. The major drawback of
the Mini ATX from memory slot and only allow one or two Dual In-Line
Memory Modules (DIMMs) to be installed.
Identifying the from factors of a motherboard can be quite difficult,
although most manufactures will label product to aid identification. Naturally
any motherboard document should clearly state the from factor.
PROGRAMMING LANGUAGESPROGRAMMING LANGUAGESPROGRAMMING LANGUAGESPROGRAMMING LANGUAGES
Hundreds of programming languages exist. Only a few, however, are
used widely enough today for the industry to recognize them as standards.
Most of these are high-level languages that work on a variety of computers.
This section discusses these programming languages, their origins, and their
primary purpose. Although the
Java programming language is used in many business applications
today; it originally was used primarily for Web development. Thus, Java is
discussed in the Web page development section of this chapter.
To illustrate the similarities and differences among programming
languages, figures on the following pages show program code in several
programming languages. The code solves a simple payroll problem —
computing the gross pay for an employee.
The steps to compute gross pay can vary from one system to another.
The examples on the following pages use a simple algorithm to help you easily
compare one programming language with another.
To compute the gross pay, first multiply the regular time hours worked
by the hourly rate of pay to obtain the regular time pay. If the employee has
overtime hours, the employee’s overtime pay is 1.5 times the hourly rate of pay
multiplied by overtime hours. Then, add the regular time pay and overtime pay
together.
BASIC
John Kemeny and Thomas Kurtz developed a programming language
called Beginner’s All-purpose Symbolic Instruction Code, or BASIC, in the
mid-1960s at Dartmouth College. Kemeny and Kurtz designed BASIC for use
as a simple, interactive problem-solving language. BASIC originally was
intended as the language used in a student’s first programming course because
it is so easy to learn and use.
Today, BASIC is used on both personal computers and mid-range
servers to develop some business applications. Many versions of BASIC exist,
including QBasic, QuickBasic, and MS-BASIC.
Visual Basic
Developed by Microsoft Corporation in the early 1990s, Visual Basic is
a Windows based
Application that assists programmers in developing other event-driven
Windows-based applications. The first step in building a Visual Basic
application is to design the graphical user interface using Visual Basic objects.
Visual Basic objects, or controls, include items such as command buttons, text
boxes, and labels.
Next, you write any code needed to define program events. An event in
Visual Basic might be the result of an action initiated by a user. When a user
clicks an object in a Visual Basic application, the application executes the
Click event. You define Visual Basic events using code statements written in
Visual Basic’s built-in programming language.
COBOL
COBOL (Common Business-Oriented Language) developed out of a
joint effort between the United States government, businesses, and major
universities in the early 1960s. Naval officer Grace Hopper, a pioneer in
computer programming, was a prime developer of the COBOL language.
COBOL is a procedural programming language designed for business
applications. Although COBOL pro grams often are lengthy, their English- like
statements make the code easy to read, write, and maintain (Figure 15-26).
COBOL is especially useful for processing transactions on main frames.
COBOL programs also run on other types of computers. The most popular
personal computer COBOL program is Micro Focus Net Express®, which
allows you to create procedural and object oriented
COBOL programs and migrate them to the Web.
C
The C programming language, developed in the early 1970s by Dennis
Ritchie at Bell Laboratories, originally was designed for writing system
software. Today, a variety of software programs are written in C. This includes
operating systems and application software such as word processing and
spreadsheet programs.
C is a powerful language that requires professional programming skills.
Many programmers use C for business and scientific problems. C runs on
almost any type of computer with any operating system, but it most often is
used with the UNIX operating system. In fact, most of the UNIX operating
system is written in C.
C++
Developed in the 1980s by Bjame Sroustrup at Bell Laboratories, C++
(pronounced SEE-plus-plus) is an object-oriented programming language. C++
is an extension of the C programming language. It includes all the elements of
the C language plus has additional features for working with objects, classes,
events, and other object oriented concepts. Programmers commonly use C++ to
develop application software, such as word processing and spreadsheet
programs, as well as database and Web applications. Although C++ is an
outgrowth of the C programming language, you do not need C programming
experience to be a successful C++ programmer.
Some programmers use a newer programming language called C#
(pronounced SEE-sharp). C# com bines features of C and C++ and is best
suited for development of Web applications.
JAVA
Developed by Sun Microsystems, Java is a compiled object-oriented
programming language used to write stand-alone applications, as well as
applets and servlets.
Java applet examples might include input forms, rotating images,
fireworks, interactive animations, or a game. Figure 15-37 shows a sample Java
program and its resulting screen.
The Java language is very similar to C++. One difference is that Java
source code is compiled into byte code, instead of object code. The operating
system cannot execute byte code. A Java interpreter executes the byte code.
Java-enabled Web browsers contain Java byte code interpreters.
Code segments used to create a Java application are called JavaBeans, or
Beans. A JavaBeans is platform independent. This enables the code to run on
any computer or operating system. Many programmers believe that Java will be
the programming language of the future because of its simplicity, robustness,
and portability.
INTEL PROCESSORS: NOW AND THENINTEL PROCESSORS: NOW AND THENINTEL PROCESSORS: NOW AND THENINTEL PROCESSORS: NOW AND THEN
There might come a time when you will have to replace or
upgrade a processor in order to fix a problem. Listed
below are details and characteristics of some of
the most popular chips from Intel and other
manufacturers.
8088
This is the chip found in most of the IBM XT-class machines. The 8088
came in a 40- pin DIP package. Translated, this means the 8088 is a small,
rectangular chip with two rows of 20 pins each. The original speed of this chip
was 5MHz. Later versions reached a top speed of about 8MHz.
80286
Introduced in 1981 by Intel, this chip became the mainstay of the AT-
class computers. The chip itself was packaged in a square called a Pin Grid
Array (PGA) instead of a rectangle.
The chip contained about 130,000 transistors -- about 100,000 more than
the 8088.
80386
The 80386 was introduced to the market in 1985 and came in two
different types: DX and SX. This chip was also packaged in the PGA
configuration. The 80386 contained
250,000 transistors and also provided features like multitasking of DOS
programs and a 32-bit data path. The 32-bit data path was available only in the
DX version, while the SX version had a 16-bit data path. This made the SX
more compatible with the 80286 computers and hardware.
80486
The 80486 chip was actually a “beefed-up” version of the 80386. The
486 processor was a composite of three other chips. The 80486 consisted of a
386 chip, a 385 cache controller and a 387 math co-processor. The 486
contained about 1.25 million transistors and 8k of internal cache memory. It
provided a 32- bit data path and a built-in math co-processor. Like the 80386,
the 80486 came in two types: the DX and SX. The 80486 SX had all the
features of the DX version minus the math co processor. Actually, the math co-
processor was still on-board but disabled in the SX version.
80486DX2
To understand the 80486DX2, it is important to understand another Intel
creation designed to increase system speed: the “Overdrive” chip. The
Overdrive chip could run at two clock speeds simultaneously. If the chip was
placed on a 486SX1 25MHz system board, it was placed in the socket for the
co processor chip and took over for the 486SX chip. When data was passed
through the Bus or memory, it was done at the speed of the processor; in this
case 25MHz. This is referred to as the external clock speed. All the internal
calculations were done at twice the 25MHz speed, at 50MHz. The 80486DX2
is very similar to the Overdrive chip in that it runs at a certain external speed
“X MHz” but performs all internal calculations at “two times X.”
80486DX4
The plot thickens. DX4 chips used a technology developed by IBM
called Clock Tripler (nicknamed “Blue Lightning”). Under an agreement with
Intel, IBM manufactured 486 chips using the Intel mask. Using their own
Clock Tripler technology, IBM took an Intel 486DX 25MHz chip and
increased its speed to approximately 75MHz.
Intel followed suit and announced the 80486DX/99MHz chip. This chip
would run external speeds of 331VIHz and perform internal calculations at
99MHz.
Pentium
In 1993 Intel introduced the Pentium processor. The initial market
response was not overwhelming, but the Pentium has now become the standard
for personal computers sold today. The Pentium processor contains over 3
million transistors and provides a 64- bit data path.
The first generation of Pentium chips was subject to heat problems.
Computers not designed to deal with high temperatures tended to experience
high failure rates.
Newer versions of the Pentium chip were designed to run cooler. System
boards and internal components were also designed to cope with the higher
temperatures.
The Pentium chips will run both internal calculations and external
processing at the same speed. Another unique feature of the Pentium chip is the
cache. The Pentium has two 8KB caches: one that is used for program code and
another used for data cache. The Pentium chip was also designed to be fault
tolerant, something Intel refers to as “superscalar.” This feature is only
functional when the Pentium chip is installed on a system board that will
support multiple processors. Fault tolerance simply means that when two
processors are present on the system board, the second chip takes over if the
first chip fails.
Pentium Pro
The Pentium Pro processor has a different look and design than the other
chips. It is the first Intel processor to combine Level1 (L1) and Level 2 (L2)
cache in the same package as the CPU. The Pentium Pro processor is a dual-
chip configuration that houses the Pentium Pro CPU on one side of the dual-
cavity package and the L2 cache memory on the other. According to Intel, this
simplifies system design and saves space. The Pentium Pro processor has about
21 million transistors in total. The CPU core has 5.5 million transistors and the
L2 cache has 15.5 million. The Pentium Pro was designed to support multiple
Pentium Pro processors connected in parallel. The Pentium Pro is a true 32-bit
processor. It operates at speeds of 200MHz.
MMX Technology
The MMX technology is based on a new set of instructions that are built
into Intel’s Pentium microprocessors. This new instruction set enables the chip
to efficiently process video and audio data. Prior to the MMX technology,
multimedia operations, in video and sound, had to be handled by separate
components like sound cards and enhanced video boards. These same functions
can now be managed by the processor.
MMX chips’ internal memory (cache memory) has doubled in size
(32KB). This is the area in memory that holds recently accessed data. It is
designed to speed up subsequent requests to this data. This means that more
instructions and data can be stored internally in the chip, reducing the number
of times the processor has to access slower external memory. Most multimedia
applications run dramatically faster and smoother. To really get the most out of
the new MMX chip, you must run the enhanced MMX applications that have
been written to exploit the true power of the technology.
Pentium II
The Pentium II processor is available in speeds from 233MHz to
450MHz. It utilizes the innovative 0.25 micron manufacturing process that
enables these CPUs to include over 7.5 million transistors. This results in more
power in less space. The processor core is packaged in the Single Edge Contact
(SEC) cartridge enabling ease of design and flexible motherboard architecture.
The processor also includes MMX technology. The Dual Independent Bus
(DIB) architecture increases bandwidth and performance over single-bus
processors.
Pentium III
The new Intel Pentium III processor is groundbreaking in terms of
graphics capabilities. The chip has been built to exploit many of the new and
expanding 3-D graphic images and their manipulation. The following are some
of the highlights of the Pentium III.
Added 70 new instruction sets for enhanced graphics, video and sound.
The Pentium III processor introduced a new processor instruction set called
Streaming SIMD Extensions (SSE). Single-instruction, Multiple Data (SIMD)
was the instruction set used by the MMX processor to improve multimedia
performance. The Pentium III SSE instruction set was designed to further
enhance multimedia performance.
An embedded serial number to help companies with an inventory of
computers. This feature will also enhance on line security transactions.
Although it also raises some very serious privacy concerns.
Clock speeds in excess of 800 MHz.
Pentium IV
Pentium 4 (P4) is the Intel processor (codenamed Willamette) that was
released in
November 2000. The P4 processor has a viable clock speed that now
exceeds 2 Gigahertz (GHz) - as compared to the 1 GHz of the Pentium 3.
P4 had the first totally new chip architecture since the 1995 Pentium
Pro. The major difference involved structural changes that affected the way
processing takes place within the chip, something Intel calls Net Burst micro
architecture. Aspects of the changes include: a 20-stage pipeline, which boosts
performance by increasing processor frequency; a rapid-execution engine,
which doubles the core frequency and reduces latency by enabling each
instruction to be executed in a half (rather than a whole) clock cycle; a 400
MHz system bus, which enables transfer rates of 3.2 gigabytes per second
(GBps); an execution trace cache, which optimizes cache memory efficiency
and reduces latency by storing decoded sequences of micro operations; and
improved floating point and multimedia unit and advanced dynamic execution,
all of which enable faster processing for especially demanding applications,
such as digital video, voice recognition, and online gaming.
P4's main competition for processor market share is the AMD Athlon
processor.
Celeron
The Celeron is Intel’s entry into the low-end microprocessor market. It
is based on the same architecture as the Pentium II. However, it lacks some of
the performance features of the Pentium II family. The newest of the Celeron
CPUs include an L1 and L2 on-board cache. This configuration means that the
cache is actually accessed at the same clock speed as the processor operates.
When comparing the Celeron’s L2 cache to the Pentium II’s cache you will
find it somewhat smaller (i28 KB) as compared to the Pentium II’s (512 KB)
cache. However, since the Celeron’s cache is built in and the Pentium’s is not,
their effective L2 speeds are roughly the same. The Celeron processor supports
clock speeds up to 466 MHz and can be mounted in a Slot 1 motherboard. Intel
is marketing this chip for the entry level PC, capable of providing performance
solutions geared to the home and light business use.
Itanium Processor
The Itanium processor, formerly known as the Merced IA- 64, is unique
with its Slot M configuration and L3 cache. The L3 cache is small in physical
size and is not located on-board the chip itself but is bundled instead within the
processor package.
Currently there are two flavors: the 800 MHz and 1000MHz versions.
Motorola Chip Family
The Motorola chip set is not quite as well known in the PC market as
Intel. For the most part, it is associated with the Apple computer line.
68000
Introduced in 1979, the 68000 chip is closely associated with the Apple
computer.
The 68000 chip employed a 32- bit design and used a 16-bit data Bus.
The 68000 was far ahead of Intel’s efforts at the time.
68010
In 1982, Motorola introduced the 68010 chip. The major difference
between the68000 and the 68010 was the addition of virtual memory support.
This chip also incorporated internal cache which made the processing of sub-
routines much faster.
This chip did not find widespread use in the computer world but was
used extensively in Motorola’s component division.
68020
This chip was introduced in 1984 as the first full 32-bit chip in the
Motorola line. The 68020 had the ability to access 4 GB of RAM and utilized
floating point processing capabilities. It was used in the Macintosh II and found
widespread use in minicomputers as well.
68030
Introduced to the market in 1987, the 68030 had all the features of the
68020 plus demand page memory management. Other enhancements to the
chip also increased the speed of the chip. It was used most widely used in the
Macintosh II series of computers.
68040
In 1989, Motorola’s answer to Intel’s 486 was the 68040.
However, the 68040 did not gain the market share that Intel’s486
enjoyed.
Power PC
Apple, IBM and Motorola all joined together to develop the PowerPC
family of chips.
PowerPC stands for Performa2 Optimization with Enhanced RISC.
Currently Apple incorporates the chip in its PowerMac series of computers.
This chip can also be used in everything from laptops to computers functioning
as servers.
Other Chips
Cyrix
Cyrix (SYE-rihks) is a family of low-end, low-cost microprocessors
intended for personal computers and personal information devices. Cyrix
competes with Intel in the low-cost, low-end market for PC microprocessors.
Typically, Cyrix has been able to under-price Intel for comparable low-end
microprocessors.
Cyrix began making semiconductors in 1988. Its first product was a
math coprocessor. About 1992, it introduced its first microprocessors that
would handle the instruction set specified by Intel’s 486 microprocessors.
AMD K6
The AMD K6 is AMD’s answer to the Intel Pentium series of
microprocessors.
Although it is considerably less expensive than the Pentium II
processors, according to many industry based benchmarks the K6 has slightly
better performance. The KG has 64K of Li and L2 cache. The K6 processor can
be mounted in a Socket 7 based motherboard.
AMD offers multiple K6 versions which support a 66 MHz bus and
operate at clock speeds starting at 166 MHz. There is also a 266 version,
referred to as the K6+. The K6+ (266) operate at about 2.5 volts of power at a
very low heat output making it an ideal candidate for the laptop computing
market.
K7 (Athlon)
The K7 processor was the first AMD product to support a 200 MHz bus
and to reach a 1 Gigahertz (one billion) clock speed. The K7 classification was
actually the development name for the Athlon processor. Compaq and Gateway
are among companies that manufacture computers that include the 1 GHz
Athlon. As the successor to AMD’s K6 microprocessor the K7 compares
favorably to Intel’s Pentium III. The K7 has a 128 KB Li and L2 cache that is
built into the chip itself, significantly increasing performance.
THE COMPONENTS OF A COMPUTERTHE COMPONENTS OF A COMPUTERTHE COMPONENTS OF A COMPUTERTHE COMPONENTS OF A COMPUTER
A computer consists of a variety of hardware components that work
together with software to perform calculations, organize data, and
communicate with other computers.
These hardware components include input devices, output devices, a
system unit, storage devices, and communications devices.
Input Devices
An input device is any hardware component that allows a user to enter
data and instructions into a computer. Six commonly used input devices are the
keyboard, mouse, microphone, scanner, digital camera, and PC camera.
A computer keyboard contains keys that allow you to type letters of the
alphabet, numbers, spaces, punctuation marks, and other symbols. A computer
keyboard also contains other keys that allow you to enter data and instructions
into the computer.
A mouse is a small handheld device that contains at least one button.
The mouse controls the movement of a symbol on the screen called a pointer.
For example, as you move the mouse across a flat surface, the pointer on the
screen also moves.
With the mouse, you can make choices, initiate a process, and select
objects.
A microphone allows a user to speak to the computer to enter data and
instructions into the computer. A scanner reads printed text and pictures and
then translates the results into a form the computer can use. For example, you
can scan a picture, and then include the picture when creating a brochure.
With a digital camera, you can take pictures and transfer the photo
graphed image to the computer, instead of storing the images on traditional
film. A PC camera is a digital video camera attached to a computer. A PC
camera allows home users to create a movie and take digital still photographs
on their computer. With a PC camera, you also can have a video telephone call
— where someone can see you while communicating with you.
Output Devices
An output device is any hardware component that can convey
information to a user. Three commonly used output devices are a printer, a
monitor, and speakers.
A printer produces text and graphics on a physical medium such as
paper or transparency film. A monitor, which looks like a television screen,
displays text, graphics, and video information. Speakers allow you to hear
music, voice, and other sounds generated by the computer.
System Unit
The system unit, sometimes called a chassis, is a box-like case made
from metal or plastic that protects the internal electronic components of the
computer from damage. The circuitry in the system unit usually is part of or is
connected to a circuit board called the motherboard.
Two main components on the motherboard are the central processing
unit and memory. The central processing unit (CPU), also called a processor, is
the electronic device that interprets and carries out the basic instructions that
operate the computer.
During processing, the processor places instructions to be executed and
data needed by those instructions into memory. Memory is a temporary holding
place for data and instructions.
Both the processor and memory consist of chips. A chip is an electronic
device that contains many microscopic pathways that carry electrical current.
Chips, which usually are no bigger than one-half inch square, are packaged so
they can be attached to a motherboard or other circuit board.
Some computer components, such as the processor, memory, and most
storage devices, are internal and reside inside the system unit. Other
components, such as the key board, mouse, microphone, monitor, printer,
scanner, digital camera, and PC camera, usually are located outside the system
unit. These devices are considered external. A peripheral is any external device
that attaches to the system unit.
Storage Devices
Storage holds data, instructions, and information for future use. Storage
differs from memory, in that it can hold these items permanently. Memory, by
contrast, holds items only temporarily while the processor interprets and
executes instructions.
A storage medium (media is the plural) is the physical material on which
a computer keeps data, instructions, and information. A storage device records
and retrieves items to and from a storage medium. Storage devices often
function as a source of input because they transfer items from storage into
memory.
Common storage devices are a floppy disk drive, a Zip® drive, a hard
disk drive, a CD-ROM drive, a CD-RW drive, a DVD-ROM drive, and a
DVD+RW drive. A drive is a device that reads from and may write on a
storage medium. This media includes floppy disks, Zip® disks, hard disks, and
compact discs.
A floppy disk consists of a thin, circular, flexible disk enclosed in rigid
plastic. A floppy disk stores data, instructions, and information using magnetic
patterns. You insert and remove a floppy disk into and from a floppy disk
drive. A Zip® disk is a higher capacity disk that can store the equivalent of up
to 170 standard floppy disks.
A hard disk provides much greater storage capacity than a floppy disk.
A hard disk usually consists of several circular platters that store items
electronically. These disks are enclosed in an airtight, sealed case, which often
is housed inside the system unit.
Some hard disks are removable, which enables you to insert and remove
the hard disk from a hard disk drive, much like a floppy disk. Removable disks
are enclosed in plastic or metal cartridges so you can remove them from the
drive. The advantage of removable media such as a floppy disk and removable
hard disk is you can take the media out of the computer and transport or secure
it.
A compact disc is a flat, round, portable medium that stores data using
microscopic pits, which are created by a laser light. One type of compact disc is
a CD-ROM, which you can access using a CD-ROM drive. A Picture CD is a
special type of CDROM that stores digital versions of photographs for
consumers.
A variation of the standard CD-ROM is the rewriteable CD, or CD-RW.
In addition to accessing data, you also can erase and store data on a CD-RW.
To use a CD-RW, you need a CD-RW drive. Another type of compact disc is a
DVD-ROM, which has tremendous storage capacities — enough for a full-
length movie. To use a DVDROM, you need a DVD drive. A variation of the
standard DYD-ROM is the rewriteable DYD, or DVD+RW.
PC Cards and memory cards are popular types of miniature storage
media. You then can transfer the items, such as the digital photographs, from
the media to your computer using a device called a card reader.
Communications Devices
Communications devices enable computer users to communicate and to
exchange items such as data, instructions, and information with another
computer.
A modem is a communications device that enables computers to
communicate usually via telephone lines or cable. Modems are available as
both external and internal devices.
Communications devices, such as modems, allow you to establish a
connection between two computers and transmit items over transmission
media, such as cables, telephone lines, or satellites.
INPUT DEVICESINPUT DEVICESINPUT DEVICESINPUT DEVICES
Keyboard devices
Offline Data Preparation Methods
Table 1 below illustrates the Data Preparation Devices with
corresponding input devices and media. These methods need special data
preparation devices. The term “Off linen is used because this activity is done
outside the computer and before input. In Sri Lanka the punch card system was
popular with the computers used from 1969 to the late 1970s. Later, it was
replaced by Key-to-Diskette systems, which are still in use in Sri Lanka at a
few places having high volume batch processing and less time critical
applications such as: Data Processing of Public Examinations, Provident Fund
applications, Census applications, Archival of high volume business documents
etc.
Input Media Input Devices Data Preparation
Devices
Punch Card Card Reader Key Punch & Verifier
Machines
Magnetic Tape Magnetic Tape Drive Key-To-Tape Encoder
or Key-To-Disk System
Magnetic diskette Diskette Reader / Drive Key-To-Diskette System
Table I – The Data Preparation Systems
Key Board Devices - On-line Terminals
The more common types of terminals are:
Visual Display Unit (VDU) or Video Terminal
VDU has ‘a television’ type screen and a keyboard. Here, input is by a
keyboard and output through display on Cathode Ray Tube (CRT). This is the
most common method of input.
General Features of a Video Terminal
01. It is an input/output (dual purpose) device.
02. The keyboard generally resembles a typewriter (QWERTY) keyboard,
but there is a wide range of variations.
03. Display clarity (Resolution) depends on the pixel density. Pixel is the
smallest display element to represent single color. Each character is formed
by combination of pixels.
04. Standard screen display includes 24 rows by 80 column character matrix
totaling 1920 characters.
05. Screen movement is generally; Line by line - Scrolling or page by page -
Paging.
06. Most of Video Terminals are ‘dumb’ terminals. New models appear now
in the market includes microprocessor with various levels of facilities.
Terminals
A terminal is a form of input (and output) device that connects you to a
mainframe or other type of computer called a host computer or server. There
are four types of terminals:
A dumb terminal can be used to input and receive data, but it cannot
process data independently. It is used only to gain access to information from a
computer. Such a terminal may be used by an airline reservations clerk to
access a mainframe computer for flight information
An intelligent terminal includes a processing unit, memory, and
secondary storage such as a magnetic disk. Essentially, an intelligent terminal
is a micro computer with communications software and a telephone hookup
(modem) or other communications link. These connect the terminal to the
larger computer or to the Internet. Microcomputers operating as intelligent
terminals are widely used in organizations.
A network terminal is also known as a thin client or network computer,
is a low-cost alternative to an intelligent terminal. Most network terminals do
not have a hard-disk drive and must rely on the host computer or server for
application and system software. These devices are becoming increasingly
popular in many organizations.
An Internet terminal, also known as a Web terminal, provides access to
the Internet and displays Web pages on a standard television set, these special
purpose terminals have just recently been introduced to offer Internet access to
people without microcomputers. Unlike the other types of terminals, Internet
terminals are used almost exclusively in the home.
A Point-of-Sale (POS) Terminal
A Point-of-Sale (POS) Terminal is a smart terminal used very much like
a cash register, but it also captures sales and inventory’s data at the point of
sale and sends it to the central computer for processing. Many supermarkets
have POS terminals that are connected directly to a central computer so that the
sales data can be immediately recorded. This type of
terminal usually displays the price, the product number,
and possibly the product description. In
addition, this type of terminal is equipped with
a cash-register-type keyboard, a cash drawer, and
a printer to print the receipt. It can operate on standalone basis and data stored
can be transferred to the main computer by using a computer medium such as a
diskette.
Banking / Financial Transaction Terminal
The most common terminals are:
01. Automatic Teller Machine (ATM)
A special intelligent terminal located outside the bank for a customer to
operate on his own to perform a limited number of banking transactions.
e.g.: cash withdrawal, cash transfers, utility bill payment etc.
02. Teller Operator terminal
This is a specialized dumb/smart terminal for the bank teller operators who
work in the front office of a bank to handle customer transactions.
03. Normal Video Terminals
Portable Terminal
It is consists of a Key Board, flat screen monitor and built in
communication software/hardware which can connect from a
remote location through a communication link to a
computer. The portability of the terminal is due to its
light weight. There are a wide range of products available.
(e.g.: Terminal for traveling salesman.)
Non Keyboard Devices
Mouse
The mouse is one of the devices connected to the computer by a small
cable. As the mouse is rolled across the desktop, the cursor moves across the
screen. When the cursor reaches the desired location, the user usually pushes
button on the mouse once or twice to signal a menu selection
or a command to the computer. Mouse technology is
often used with graphics- oriented personal computers. With
special software for graphics, the mouse can be used
like a pen or a Paint Brush to create figures and patterns
directly on the video display screen. e.g.: use with Corel Draw or Howard
Graphics, Desk Top Publishing Applications etc.
Joystick
It is a device which contains lever which can be used to
move objects on the screen.
e.g.: It is normally used to play computer games.
Light Pen
The light pen is a special attachment to a graphics terminal. The pen is
touched on the video display screen at the desired location and
switched on, and then you can draw the image on the screen.
Light pens are frequently used by graphic designers, illustrators,
and drafting engineers. Of course, data may also be entered using
keyboard e.g. Computer Aided Design (CAD), Architectural applications etc.
Touch Screen
Limited amounts of data can be entered via a terminal or a
microcomputer that has a touch screen. The user simply
touches the screen at the desired locations, marked by
labeled boxes, to point out” choices to the computer. e.g.:
Inquiry Terminals for general public such as
Terminals located in the lobby areas of a large building complex. This will
enable users to operate without much technical knowledge & skill.
Scanning Devices
Scanners
A Digital Scanner translates images such as pictures or documents into
digital form. This is one area where substantial research &
development has been taking place in the recent past.
A wide variety of products are now available in the
marketplace. The most common products are:
Hand Held Scanner
Used mostly with small scale publishing (Desk Top
Publishing) systems to input pictures, logos etc.
Flat Bed Scanner
Used to input text based documents with or
without images. Special software packages are now
available to process these text based images such as
editing, merging etc.
Character Scanners
These are hand held devices which can read data printed in special type
fonts (e.g.: OCR) or hand written data based on recommended guidelines. In
addition, there are Optical Character Readers which operate at high speed to
handle high volume batch oriented input like Electricity billing meter readings.
Optical Character Recognition (OCR)
Optical character recognition is a device that is used to scan the text,
which is found on a document, and then the data is converted into electrical
signals for the computer. This device can be used to read a special type of font.
However, the more expensive OCR devices can read a variety of fonts; some
can even read hand written documents.
Optical Mark Recognition (OMR)
The input device is Optical Mark Reader. In some of the foreign
examinations like SAT or TOEFL the candidate application forms as well as
the answer sheets are specially designed (Mark Sense Cards) to record data by
using pencil marks. Open University of Sri Lanka and University of Colombo
BIT program also use a similar method. Data recorded in this form is converted
into computer-usable form by an Optical Mark Reader (OMR). The OMR
device has a high-intensity light inside which is directed in the form of a beam
at the sheet of paper being fed through it. The beam scans the marked forms
and detects the number and location of the pencil marks. The data is then
converted into electrical signals for the computer. OMRs come in a variety of
sizes and shapes that depend on the size of the forms to be read and the
required loading and processing capacity of the reader.
Magnetic-Ink Character Recognition (MICR)
This is specially designed for the input of high volume cheques in the
banking industry. The advantages of the MICR system are that Human
involvement is minimum, thus the potential for errors is small, The codes can
be read by both people and machines, It is fast, automatic, and reliable (2400
checks/mm). The cheque leaf taken into the machine, and magnetize the ferric
particles present in the data printed at the bottom edge of it. At the first read
station it recognizes data based on magnetic induction & converts into
electrical signals. Generally at the second read station it reads again & compare
with the first reading for accuracy. In addition to reading, it sort the cheque
leaves in a bundle according to the bank code & output to respective pigeon
holes. e.g.; Cheque Clearing House of Sri Lanka.
Bar Code Reader
Bar Code is a collection of thick and thin lines and spaces that represent
data in binary.
E.g.:
• Parcel tracking system in courier companies
• File tracking system in an office
• Issue of items in a supermarket.
• Record the movement of books in a library
In courier application the parcel reference number is bar coded &
recorded in all relevant documents & the parcel it. This reference number is
input to the computer system by using a portable barcode scanner or wand
reader. The wand has a scanning device that analyzes light & dark bars for
width & spacing. This wand reader is a special attachment to a video terminal.
Card Reading Devices
Time/Punch Card
IBM made the punch-card technology into the business standard of the
1950's and 1960's. There are manual punch card readers available. But now a
day this technology is not using widely.
Voice and Image Input Devices
Microphone
A microphone wants to take varying
pressure waves in the air and convert them into
varying electrical signals. There are five different
technologies commonly used to accomplish this
conversion:
Carbon microphones
The oldest and simplest microphone uses carbon dust. This is the
technology used in the first telephones and is still used in some telephones
today. The carbon dust has a thin metal or plastic diaphragm on one side. As
sound waves hit the diaphragm, they compress the carbon dust, which changes
its resistance. By running a current through the carbon, the changing resistance
changes the amount of current that flows.
Dynamic microphones
A dynamic microphone takes advantage of electromagnet effects. When
a magnet moves past a wire (or coil of wire), the magnet induces current to
flow in the wire. In a dynamic microphone, the diaphragm moves either a
magnet or a coil when sound waves hit the diaphragm, and the movement
creates a small current. Ribbon microphones - In a ribbon microphone, a thin
ribbon is suspended in a magnetic field. Sound waves move the ribbon which
changes the current flowing through it.
Condenser microphones
A condenser microphone is essentially a capacitor, with one plate of the
capacitor moving in response to sound waves. The movement changes the
capacitance of the capacitor, and these changes are amplified to create a
measurable signal. Condenser microphones usually need a small battery to
provide a voltage across the capacitor.
Crystal microphones
Certain crystals change their electrical properties as they change. By
attaching a diaphragm to a crystal, the crystal will create a signal when sound
waves hit the diaphragm.
Web Camera
A cam, home cam, or Webcam is a video camera, usually attached
directly to a computer, whose current or latest image is request able from a
Web site. A live cam is one that is continually providing new images that are
transmitted in rapid succession or, in some cases, in streaming video. Sites with
live cams sometimes embed them as Java applets in Web pages.
Cams have caught on; there are now (we estimate)
several thousand sites with cams. The first cams
were positioned mainly on fish tanks and coffee
machines. Many of today's live cams are on sex
oriented sites. For travel promotion, traffic information, and the
remote visualization of any ongoing event that's interesting, webcams seem like
an exciting possibility that will become more common as users get access to
more bandwidth.
OUTPUT DEVICESOUTPUT DEVICESOUTPUT DEVICESOUTPUT DEVICES
Monitors
Mono (Monochrome) – Display a single Color.
CGA - Color Graphic Adapter (4 Colors)
EGA – Enhance Graphic Adapter (16 Colors)
VGA – Video Gr. Ad. (16 colors & 256 shading)
SVGA – Super VGA
Printers
Impact Printers
The Print mechanism strikes against the paper.
Non Impact Printers
The Print mechanism does not strike against the ribbon or paper.
Character Printers
Speed in Characters per Second (CPS)
Used for low to medium volume applications
E.g.: Matrix, Ink Jet.
Line Printers
Speed in Lines per Minute (LPM)
Used for high volume medium quality applications.
E.g.: printing of public examination results.
Page Printers
Speed in Pages per Minute (PPM)
Used for medium to high volume, high quality applications.
E.g.: Print a master copy of a magazine by using a Laser Printer.
Color Printers
Color printers use a Color Cartridge. Time to
time you have to place the cartridge when the
cartridge is over.
Black and White Printers
Black and White Printers use a Black and White Cartridge. Time to time
you have to place the cartridge when the cartridge is over. There are printers
which supports both Color and Black and White cartridges.
Text Printers
To print text there are specially text printers. The quality is very low in
these printers.
Graphic Printers
These are very high quality printers. These printers are expensive than
normal printers. You can get very high quality Images printouts by using a
graphic printer.
Graphic designers and the people in studios use Graphic printers.
Dot Matrix Printers
The most widely used printer which prints one
character at a time. The technology has improved
during the recent past to include very high quality &
reasonably fast printers.
Daisy Wheel Printers
A kind of impact printer where the characters are arranged on the ends
of the spokes of a wheel (resembling the petals on a daisy).
The wheel (usually made of plastic) is rotated to select the character to
print and then an electrically operated hammer mechanism bends the selected
spoke forward slightly, sandwiching an ink ribbon between the character and
the paper, as in a typewriter.
One advantage of this arrangement over that of a typewriter is that
different wheels may be inserted to produce different typefaces.
Inkjet Printers
Ink printers work in much the same fashion as dot-matrix printers in that
they form images or characters with little dots. However,
the dots are formed, not by hammer like pins, but by
tiny droplets of ink, and the text these printers produce is of
letter quality. These printers can almost match the speed of dot- matrix printers
- up to about 270 eps-and they produce less noise.
Thermal Printers
Thermal printers use heat to produce an image
on special paper. The print mechanism - rather like a
dot - matrix print head - is designed to heat the
surface of chemically treated paper so that a dot is
produced based on the reaction of the chemical to the
heat. No ribbon or ink is involved. It can print multiple colors.
Laser Printers
Laser printer technology is much less mechanical than
impact printers resulting in much higher speeds and
quieter operation. The process resembles the operation
of a photocopy machine. A laser beam is directed across
the surface of a light-sensitive drum and fixed as needed
to record an image in the form of a pattern of tiny dots.
The image is then transferred to the paper. This printer prints a page at a
time - in the same fashion as a copying machine, using a special toner. When
high-speed laser printers (also called page printers) were introduced, they were
very expensive. However, recent laser printer technology has made desktop
versions available at very reasonable prices.
Plotters
A plotter is a specialized output device designed to produce high-quality
graphics in a variety of colors. Drum plotters and flat bed plotters both use pens
and electrostatic plotters do not.
Drum Plotter
The paper is mounted on the surface of a drum. The drum revolves and
the plotter pens (which are similar to felt-tip pens) are horizontally positioned
over the target area. When the paper has rotated to the correct point, the pens
are dropped to the surface moved left and right under program control across
the paper as the drum revolves. When the image is complete,
the pens are raised from the surface.
Flat Bed Plotter
These are designed so that the paper is placed flat and one or
more pens move horizontally and vertically across the paper.
Electrostatic Plotters
Use electrostatic charges to create images out of very small dots on
specially treated paper. Electrostatic plotters are faster than pen plotters and can
produce images of very high resolution, e.g.: Used by Architects, Surveyors,
and Engineers.
Voice Output Devices
Voice output should be a more
useful medium. This technology has
had to overcome many hurdles. The
most difficult has been that every
individual perceives speech
differently; that is, the voice patterns,
pitches, and reflections we can hear
and understand are different for all of us. It is not always easy to understand an
unfamiliar voice pattern. At this point, two different approaches to voice output
have evolved:
Speech coding
This relies on human speech as a reservoir of sounds to draw from in
building the words and phrases to be output. Sounds are codified and stored on
disk to be retrieved and translated back as sounds. Speech coding has been used
in applications such as automobiles, toys, and games.
Speech synthesis
In this method voice is produced electronically without the use of a
human voice. The largest application to date for the speech synthesis approach
to voice output converting text into “spoken” words has many potential uses,
including providing reading machines for the blind. And, of course, sound
output does not have to be in voice form, it can be music or special-effects
sounds, such as the sound accompaniment for computer animation, in cartoons
etc.
COM Devices
Serial port or "com port". A connector on a computer to which you can
attach a serial line connected to peripherals which communicate using a serial
(bit-stream) protocol.
The most common type of serial port is a 25-pin D-type connector
carrying EIA-232 signals. Smaller connectors (e.g. 9-pin D-type) carrying a
subset of EIA-232 are often used on personal computers. The serial port is
usually connected to an integrated circuit called a UART which handles the
conversion between serial and parallel data.
In the days before bit-mapped displays, and today on multi-user
systems, the serial port was used to connect one or more terminals
(teletypewriters or VDUs), printers, modems and other serial peripherals.
Two computers connected together via their serial ports, possibly via modems,
can communicate using a protocol such as UUCP or CU or SLIP.
CPU (CENTRAL PROCESSING UNIT)CPU (CENTRAL PROCESSING UNIT)CPU (CENTRAL PROCESSING UNIT)CPU (CENTRAL PROCESSING UNIT)
Processor
A processor is the logic circuitry that responds to
and processes the basic instructions that drive a
computer. The term processor has generally replaced
the term central processing unit (CPU). The processor
in a personal computer or embedded in small devices is often called a
microprocessor.
Arithmetic and Logic Unit
An arithmetic-logic unit (ALU) is the part of a computer processor
(CPU) that carries out arithmetic and logic operations on the operands in
computer instruction words. In some processors, the ALU is divided into two
units, an arithmetic unit (AU) and a logic unit (LU). Some processors contain
more than one AU - for example, one for fixed-point operations and another for
floating-point operations. (In personal computers floating point operations are
sometimes done by a floating point unit on a separate chip called a numeric
coprocessor.)
Typically, the ALU has direct input and output access to the processor
controller, main memory (random access memory or RAM in a personal
computer), and input/output devices. Inputs and outputs flow along an
electronic path that is called a bus. The input consists of an instruction word
(sometimes called a machine instruction word) that contains an operation code
(sometimes called an "op code"), one or more operands, and sometimes a
format code. The operation code tells the ALU what operation to perform and
the operands are used in the operation. (For example, two operands might be
added together or compared logically.) The format may be combined with the
op code and tells, for example, whether this is a fixed-point or a floating-point
instruction. The output consists of a result that is placed in a storage register
and settings that indicate whether the operation was performed successfully. (If
it isn't, some sort of status will be stored in a permanent place that is sometimes
called the machine status word.) In general, the ALU includes storage places
for input operands, operands that are being added, the accumulated result
(stored in an accumulator), and shifted results.
The flow of bits and the operations performed on them in the subunits of
the ALU is controlled by gated circuits. The gates in these circuits are
controlled by a sequence logic unit that uses a particular algorithm or sequence
for each operation code. In the arithmetic unit, multiplication and division are
done by a series of adding or subtracting and shifting operations. There are
several ways to represent negative numbers. In the logic unit, one of 16
possible logic operations can be performed - such as comparing two operands
and identifying where bits don't match. The design of the ALU is obviously a
critical part of the processor and new approaches to speeding up instruction
handling are continually being developed.
Control Unit
Control Unit controls every single hardware part attached to the
computer. Its main task is controlling the hardware devices which are attached
to the machine according to the signals of CPU.
LOGICAL STRUCTURE OF A COMPUTERLOGICAL STRUCTURE OF A COMPUTERLOGICAL STRUCTURE OF A COMPUTERLOGICAL STRUCTURE OF A COMPUTER
BACKING STORAGE
INTERNAL STORAGE OUTPUT
CONTROL UNIT
ARITHMETIC &
LOGICAL
UNIT.
INPUT
HOW COMPUTERS WORK?HOW COMPUTERS WORK?HOW COMPUTERS WORK?HOW COMPUTERS WORK?
Computers process information using the instructions from the user to
produce the desired results. The instruction that you feed in the computer,
through software, is the basic input. This input could be fed through a keyboard
or a mouse or a scanner, etc. These instructions are then sent to the processor
know as the central processing unit for processing. By processing, broadly we
mean carrying out of instructions for a task to be completed. After the task or
processing has been performed, the processor send, the result, know as the
output to the screen or the printer, as desired by you want to store the
information for any future use you can very well store it either on the hard disk
or any other storage device like floppy disk etc. the illusion, that follows makes
the whole procedure more clear.
BOOTING PROCESSBOOTING PROCESSBOOTING PROCESSBOOTING PROCESS
Booting the Computer
The PC boot process starts when a small program within the BIOS chip
looks for an active partition and loads the operating system. There are two
methods for booting a computer: cold and warm booting.
Cold Boot
Cold booting occurs when the computer’s power switch is turned on.
The effect of a cold boot is that it brings the system to the very beginning of the
boot process, beginning with the POST. This may become necessary when the
computer stops responding to any commands, including warm boots.
Warm Boot
A warm boot bypasses the first two system tests and goes directly to the
bootstrap loader (the point where DOS loads). A warm boot is triggered by
pressing the Ctrl, Alt, and Del keys at the same time.
CTRL + ALT + DEL
Rebooting the computer should be used only as a last resort. Any
information in open application files could be lost when rebooting takes place.
Creating Boot Disks
Every once in a blue moon your system may refuse to boot. There are
numerous reasons that could cause this. If you are prepared with an emergency
boot disk for such an occasion, you will save yourself a lot of anxious moments
The steps for preparing a boot disk are as follows:
1. Format a floppy disk using the IS switch. Put a blank diskette into your
floppy drive.
2. Type format A: /S
3. Copy the AUTOEXEC.BAT and CONFIG.SYS files to the newly
4. /S-formatted disk.
5. Copy any files and drivers that are essential to the boot process such as
IO.SYS, COMMAND.COM and other files necessary for your particular
system.
Label the disk appropriately and write protect it by flipping the black
switch on the bottom of the diskette. Store the disk in a safe and readily
accessible spot. By default, every time the computer is started, it searches in
drive A for a bootable floppy disk. In the event that the hard drive does not
boot, you are able to access the system from drive A. This allows you the
opportunity to look for the problem.
OPERATING SYSTEMOPERATING SYSTEMOPERATING SYSTEMOPERATING SYSTEM
Operating System Concepts
Many of the first operating systems were device dependent and
proprietary. A device dependent software product is one that runs only on a
specific type or make of computer. Proprietary software is privately owned and
limited to a specific vendor or computer model. When manufacturers
introduced a new computer or model, they
often produced an improved and different
proprietary operating system. Problems
arose, however, when a user wanted to
switch computer models or manufacturers.
The user’s application soft ware often
would not work on the new computer
because the applications were designed to
work with a specific operating system.
Some operating systems still are device dependent. The trend today,
however, is toward device- independent operating systems that run on
computers provided by a variety of manufacturers. The advantage of device-
independent operating systems is you can retain existing application software
and data files even if you change computer models or vendors. This feature
generally represents a sizable savings in time and money. New versions of an
operating system usually are downward compatible. A downward compatible
operating system is one that recognizes and works with application software
written for an earlier version of the operating system. The application software,
by contrast, is said to be upward compatible. An upward- compatible product is
written for an earlier version of the operating system, but also runs with the
new version. The three basic categories of operating systems that exist today
are stand-alone, network, and embedded. The table in Figure 8-18 lists names
of operating systems in each category. The following pages discuss the
operating systems listed in the table.
Stand-Alone Operating Systems
A stand-alone operating system is a complete operating system that works on a
desktop or notebook computer. Some stand-alone operating systems, called
client operating systems, also work in conjunction with a network operating
system. That is, client operating systems can operate with or without a network.
Examples of stand-alone operating systems are DOS, Windows 3.x, Windows
95, Windows NT Workstation, Windows 98, Windows 2000 Professional,
Windows Millennium Edition, Windows XP Home Edition, Windows XP
Professional Edition, Mac, OS X, OS/2 Warp Client, UNIX, and Linux. The
following paragraphs briefly discuss most of these operating systems. The
section that covers network operating systems discusses UNIX and Linux.
Loading an Operating System
The "boot" process comes from the term "boot strap". It is a play on the
concept of pulling one's self up by one's own boot straps. What actually
happens is that when the computer is powered up, the CPU runs the startup
code implanted in the system's ROM BIOS (Read Only Memory Basic Input
Output System). This startup program contains the code that tests the computer
and sets up the hardware for use.
Its last step is to load and run a program stored on the first sector of the first
drive. This is the master boot record (MBR), and the program is the master
boot program (MBP). The MBP looks to see where the primary partitions are
and which one is set as the active partition. The active partition has its own
boot record, and this contains a program designed to start the operating system
located on that partition. A partition boot record is usually referred to as the
partition root super block.
Popular Operating Systems
Stand-alone
� DOS
� Windows 3.x
� Windows 95
� Windows NT Workstation
� Windows 98
� Windows 2000 Professional
� Windows Millennium Edition
� Windows XP Home Edition
� Windows XP Professional Edition
� Mac OS X
� OS/2 Warp Client
� UNIX
� Linux
Network
� Netware
� Windows NT Server
� Windows 2000 Server
� Windows.NET Server
� OS/2 Wrap Server for E-business
� UNIX
� Linux
� Solaris
Embedded
� Windows CE
� Pocket PC 2002
� Palm OS
DOS (Disk Operating System)
The term DOS (Disk Operating System) refers to several single user operating
systems developed in the early 1980s for personal computers. The two more
widely used versions of DOS were PC-DOS and MS-DOS. Microsoft
Corporation developed both PC-DOS and MS-DOS. The functionality of these
two operating systems was essentially the same. The basic difference between
PC-DOS and MS-DOS was the type of computer on which they were installed.
Microsoft developed PC-DOS (Personal Computer DOS) for IBM, which in
turn installed and sold PC-DOS on its computers. At the same time, Microsoft
marketed and sold MS-DOS (Microsoft DOS) to makers of IBM-compatible
PCs.
DOS used a command-line interface when Microsoft first developed it. Later
versions included both command-line and menu-driven user interfaces, as well
as improved memory and disk management. At its peak, DOS was a widely
used operating system, with an estimated 70 million computers running it.
Today, DOS no longer is widely used because it does not offer a graphical user
interface (GUI) and it cannot take full advantage of modern 32-bit personal
computer processors.
Windows 98
Microsoft developed an upgrade to the Windows 95 operating system, called
Windows 98. The Windows 98 operating system was more integrated with the
Internet than Windows 95. For example, Windows 98 included Microsoft
Internet Explorer, a popular Web browser. The Windows 98 file manager,
called Windows Explorer, and also had a Web browser look and feel. With
Windows 98, you could have an Active Desktop interface, which allowed you
to set up Windows so icons on the desktop and file names in Windows
Explorer worked similar to Web Links.
Windows 98 also provided faster system startup and shutdown, better file
management, and support for multimedia technologies such as DVD and
WebTV™ (today known as MSN® TV). Windows 98 supported USB, so you
easily could add and remove devices in your computer.
Windows NT
Windows NT Workstation
Microsoft developed Windows NT Workstation as a client operating system
that could connect to a Windows NT Server. Windows NT, also referred to as
NT, was an operating system designed for client! Server networks. Windows
NT Workstation had a Windows 95 interface. Thus, users familiar with
Windows 95 easily could migrate to Windows NT Workstation. Businesses
most often used Windows NT Workstation.
Windows NT Server
As previously mentioned, Microsoft developed Windows NT as an operating
system for client/server networks. The server in this environment used
Windows NT Server. The client computers used Windows NT Workstation or
some other stand-alone version of Windows.
Start and Login
In order to get your computer to work you need both hardware and software.
An operating system is software that you use in order to communicate with the
computer’s hardware such as the mouse, the keyboard and the computer’s
memory. Your computer must have the operating system software installed
before you can perform any operations. The operating system automatically
starts when you switch on the computer. The startup process is called booting.
Most operating systems provide built-in security, which ensures that only
authenticated users can access the computer. Thus whenever you start your
computer you must provide your valid user name and password. This attempt is
known as “logging on” and the entire process of verification is known as the
“logon process”. This process helps to protect your documents from
unauthorized users.
1. Switch on the computer (The “Welcome to Windows” screen will be
displayed)
2. Press Ctrl+Alt+Delete to open the “Log On to Windows” dialog box
3. In the “User Name” box, enter your user name
4. In the “Password” box, enter your password
5. Click OK
Use Mouse (Buttons)
The mouse is an input device you can use to perform various tasks such as
opening applications, selecting items, copying data, and moving data. The
mouse moves on a flat surface, usually a mouse pad. As you move the mouse, a
mouse pointer moves in the same direction on the screen. By default, the left
mouse button is the primary mouse button. You use the left mouse button for
selecting, moving and opening objects. If you are a left hander you may
configure the right mouse button as the primary mouse button if you need to.
The following table shows the mouse actions and how to perform them with
the left mouse button as the primary button.
Mouse Action How
Point Place the mouse pointer over an object.
Click Press and release the left mouse button.
Double Click Press and release the left mouse button two times in
rapid succession.
Drag While holding down the left mouse button, move the pointer
to your desired location, and then release the button.
Right Click Press and release the right mouse button.
Pointing
Place the mouse pointer over an object
Clicking
Press and release the left mouse button.
Dragging
While holding down the left mouse button, move the pointer to your desired
location, and then release the button.
Use Keyboard (Special Keys for Windows)
The key board is the most often used input device. There are some special keys
on the keyboard that will allow you to perform some frequent tasks.
Some of those are listed below.
1. The windows key: To open the start menu
2. Ctrl+Esc: To open the start menu
3. Ctrl+C: To copy a selected item
4. Ctrl+X: To cut a selected item
5. Ctrl+V: To paste a selected item
6. Ctrl+P: To print
7. The Caps Lock: To change case
8. Alt+F4: To close the current window/ Exit/ Shut Down
Shutting Down Your Computer
1. Click on the Start Button
2. Select Shut Down
3. Select OK
SYSTEM SOFTWARESYSTEM SOFTWARESYSTEM SOFTWARESYSTEM SOFTWARE
Computer Software
Software, also called a computer program or simply a program, is a
series of instructions that tells the hardware of a computer what to do. Some
instructions allow you to input data from the keyboard and direct the computer
to store the data in memory. Other instructions cause data in memory to be
used in calculations such as adding a series of numbers to obtain a total. Some
instructions compare two values in memory and direct the computer to perform
alternative operations based on the results of the comparison. Other instructions
direct the computer to print a report, display information on the monitor, draw
a color picture on the monitor, or store information on a disk.
A computer carries out, or executes, the instructions in a pro gram by
first placing, or loading, the instructions into the memory of the computer.
Usually, the computer loads the instructions from storage into memory. For
example, each time a program executes, it might load from the hard disk into
memory.
When you purchase a program, you typically receive media such as a -
CD-ROM(s) or a DYD-ROM that contains the software. Some programs can
load into memory directly from the media. With other programs, you must
install a part or all of the soft ware on the computer’s hard disk before you can
use the program. Some programs also require you to insert the media, such as a
CD-ROM, into the drive while you use, or run, the program. Others do not.
This program requires a CD-ROM in the CD-ROM drive. When you buy a
computer, it usually has some software pre installed on its hard disk. This
enables you to use the computer as soon as you set it up. Software is the key to
productive use of computers. With the proper software, a computer can become
a valuable tool. The two categories of software are system software and
application software. The following pages describe these categories of
software.
System Software
System software consists of the programs that control the operations of
the computer and its devices. System software serves as the interface between
the user, the application software, and the computer’s hard ware. Two types of
system software are the operating system and utility programs.
Operating System
An operating system (OS) is a set of programs containing instructions
that coordinate all the activities among computer hardware devices. The
operating system also contains instructions that allow you to run application
software. Many of today’s computers use Microsoft’s most recent operating
system, called Windows XP. When you start a computer, the operating system
loads into memory from the computer’s hard disk. It remains in memory while
the computer is running and allows you to communicate with the computer and
other software.
Utility Programs
A utility program is a type of system soft ware that performs a specific
task, usually related to managing a computer, its devices, or its programs. An
example of a utility program is an uninstaller, which removes a program that
has been installed on a computer. Most operating systems include several
utility programs for managing disk drives, printers, and other devices. You also
can buy stand-alone utility programs, which allow you to perform additional
computer management functions.
Language Translators
The programs written by using a computer programming language
should be converted to the machine code in order to run the program correctly
and to get the wanted output. Computer programming languages are in human
understandable for mat and machine code cannot be understood by human.
Converting Human readable format computer programs in to machine readable
format is done by Language Translators.
Translators we can basically divide in to two parts called Compilers and
Interpreters. The main difference between these two is the way that they
convert the Computer programming language to machine language.
Compiler
A compiler is a special program that processes statements written in a
particular programming language and turns them into machine language or
"code" that a computer's processor uses. Typically, a programmer writes
language statements in a language such as Pascal or C one line at a time using
an editor. The file that is created contains what are called the source statements.
The programmer then runs the appropriate language compiler, specifying the
name of the file that contains the source statements.
When executing (running), the compiler first parses (or analyzes) all of
the language statements syntactically one after the other and then, in one or
more successive stages or "passes", builds the output code, making sure that
statements that refer to other statements are referred to correctly in the final
code. Traditionally, the output of the compilation has been called object code
or sometimes an object module. (Note that the term "object" here is not related
to object-oriented programming.) The object code is machine code that the
processor can process or "execute" one instruction at a time. More recently, the
Java programming language, a language used in object-oriented programming,
has introduced the possibility of compiling output (called byte code) that can
run on any computer system platform for which a Java virtual machine or byte
code interpreter is provided to convert the bytecode into instructions that can be
executed by the actual hardware processor. Using this virtual machine, the
bytecode can optionally be recompiled at the execution platform by a just-in-
time compiler. Traditionally in some operating systems, an additional step was
required after compilation - that of resolving the relative location of
instructions and data when more than one object module was to be run at the
same time and they cross-referred to each other's instruction sequences or data.
This process was sometimes called linkage editing and the output known as a
load module.
A compiler works with what are sometimes called 3GL and higher-level
languages . An assembler works on programs written using a processor's
assembler language.
Interpreter
An interpreter is a computer program that executes other programs. This
is in contrast to a compiler which does not execute its input program (the
source code) but translates it into executable machine code (also called object
code) which is output to a file for later execution. It may be possible to execute
the same source code either directly by an interpreter or by compiling it and
then executing the machine code produced.
It takes longer to run a program under an interpreter than to run the
compiled code but it can take less time to interpret it than the total required to
compile and run it. This is especially important when prototyping and testing
code when an editinterpret-debug cycle can often be much shorter than an edit-
compile-run-debug cycle. Interpreting code is slower than running the
compiled code because the interpreter must analyze each statement in the
program each time it is executed and then perform the desired action whereas
the compiled code just performs the action. This run-time analysis is known as
"interpretive overhead". Access to variables is also slower in an interpreter
because the mapping of identifiers to storage locations must be done repeatedly
at run-time rather than at compile time.
DBMS Software
A database is a collection of data organized in a manner that allows
access, retrieval, and use of that data. In a manual database, you might record
data on paper and store it in a filing cabinet. With a computerized database, the
computer stores the data in an electronic format on a storage medium such as a
floppy disk or hard disk. Database software, also called a database management
system (DBMS), is software that allows you to create, access, and manage a
database. Using database software, you can add, change, and delete data in the
database; sort and retrieve data from the database; and create forms and reports
using the data in the database.
APPLICATION SOFTWAREAPPLICATION SOFTWAREAPPLICATION SOFTWAREAPPLICATION SOFTWARE
Application Software
Application software consists of programs that perform specific tasks for
users. Popular application software includes word processing software,
spreadsheet software, data base software, and presentation graphics software.
Word processing software allows you to create documents such as letters,
memorandums, and brochures. Spreadsheet software allows you to calculate
numbers arranged in rows and columns. Users perform financial tasks such as
budgeting and forecasting with spreadsheet software. Database soft ware
allows you to store data in an organized fashion, as well as retrieve,
manipulate, and display that data in a variety of formats. With presentation
graphics software, you create documents called slides that add visual appeal to
presentations. Software vendors often bundle and sell these four applications
together as a single unit. This bundle, called a suite, costs much less than if you
purchased the applications individually. Microsoft’s Office XP is a very
popular suite.
Many other types of application software exist that enable users to
perform a variety of tasks. Some widely used applications include the
following: reference, education, and entertainment; desktop publishing; photo
and video editing; multimedia authoring; network, communications, electronic
mail (e-mail), and Web browsers; accounting; project management; and
personal information management. Application software is available in a
variety of forms: packaged, custom, freeware, public domain, shareware, and
from application service providers.
Word Processing
� Microsoft Word
� Corel WordPerfect
� Lotus Word Pro
� Microsoft Pocket Word
Spread Sheet
� Microsoft Excel
� Corel Quattro Pro
� Lotus 123
� Microsoft Pocket Excel
Database
� Microsoft Access
� Corel Paradox
� Lotus Approach
� Microsoft Visual FoxPro
� Oracle
Presentation Graphics
� Microsoft PowerPoint
� Corel Presentations
� Lotus Freelance Graphics
Personal Information Manager
� Microsoft Outlook
� Corel CENTRAL
� Lotus Organizer
� Palm Multi Mail
Software Suite
� Microsoft Office
� Corel WordPerfect Office
� Lotus SmartSuite
Project Management
� Microsoft Project
� Primavera Sure Track Project Manager
Accounting
� Intuit QuickBooks
� Peachtree Col11plete Accounting
� Tally
Application Packages
Copyrighted application or system software that meets the needs of a
wide variety of users, not just a single user or company, is called packaged
software. You can purchase packaged software from stores that sell computer
products. You also can purchase packaged software from companies on the
Internet.
Custom-Made Software
Sometimes a user or company with unique soft ware requirements
cannot find packaged software that meets all its needs. In this case, the person
or company can opt for custom software. Custom software, written by a
programmer, is a tailor-made application or system program developed at a
user’s request to perform specific functions.
Freeware in Public-Domain
Software and Shareware
Freeware is application or system software provided at no cost to a user
by an individual or a company. Freeware is copyrighted. You cannot resell it as
your own. Public- domain software also is free software, but it has been
donated for public use and has no copyright restrictions. Shareware is
copyrighted software that is distributed free for a trial period. If you want to
use a shareware program beyond that period, you send a payment to the person
or company that developed the program. Companies that develop shareware
rely on the honor system. The company trusts you to send payment if you
continue to use the software beyond the stated trial period. Upon sending this
small fee, the developer registers you to receive service assistance and updates.
Examples of shareware, freeware, and public-domain software include
utility programs, graphics programs, and games. Thousands of these pro grams
are available on the Internet to download, or copy to your computer. You also
can obtain copies of these programs from the developer, a coworker, or a
friend.
Application Service Provider
Storing and maintaining programs can be a costly investment for individuals
and businesses. Some opt to use an application service provider for their
software needs. An application service provider (ASP) is a third-party company
that manages and distributes software and services on the Internet. That is,
instead of installing the software on your computer, you run the programs from
the Internet. Some vendors pro vide access to the software at no cost. Others
charge for use of the program.
INTRODUCTION TO COMPUTER VIRUSESINTRODUCTION TO COMPUTER VIRUSESINTRODUCTION TO COMPUTER VIRUSESINTRODUCTION TO COMPUTER VIRUSES
A virus is a piece of programming code usually disguised as something
else that causes some unexpected and usually undesirable event. A virus is
often designed so that it is automatically spread to other computer users.
Viruses can be transmitted as attachments to an e-mail note, as downloads, or
be present on a diskette or CD. The source of the e-mail note, downloaded file,
or diskette you've received is often unaware of the virus. Some viruses wreak
their effect as soon as their code is executed; other viruses lie dormant until
circumstances cause their code to be executed by the computer. Some viruses
are playful in intent and effect ("Happy Birthday, Ludwig!") and some can be
quite harmful, erasing data or causing your hard disk to require reformatting.
Generally, there are three main classes of viruses:
Boot Sector
These viruses infect executable code found in certain system areas on a
disk. They attach to the DOS boot sector on diskettes or the Master Boot
Record on hard disks.
A typical scenario (familiar to the author) is to receive a diskette from an
innocent source that contains a boot disk virus. When your operating system is
running, files on the diskette can be read without triggering the boot disk virus.
However, if you leave the diskette in the drive, and then turn the computer off
or reload the operating system, the computer will look first in your A drive,
find the diskette with its boot disk virus, load it, and make it temporarily
impossible to use your hard disk. (Allow several days for recovery.) This is
why you should make sure you have a bootable floppy.
File
Some file infector viruses attach themselves to program files, usually
selected .COM or .EXE files. Some can infect any program for which
execution is requested, including .SYS, .OVL, .PRG, and .MNU files. When
the program is loaded, the virus is loaded as well. Other file infector viruses
arrive as wholly-contained programs or scripts sent as an attachment to an e-
mail note.
Trojan Horse
Trojan horse attacks pose one of the most serious threats to computer
security. If you were referred here, you may have not only been attacked but
may also be attacking others unknowingly. This page will teach you how to
avoid falling prey to them, and how to repair the damage if you already did.
According to legend, the Greeks won the Trojan war by hiding in a huge,
hollow wooden horse to sneak into the fortified city of Troy. In today's
computer world, a Trojan horse is defined as a "malicious, security-breaking
program that is disguised as something benign". For example, you download
what appears to be a movie or music file, but when you click on it, you unleash
a dangerous program that erases your disk, sends your credit card numbers and
passwords to a stranger, or lets that stranger hijack your computer to commit
illegal denial of service attacks like those that have virtually crippled the
DALnet IRC network for months on end.
The following general information applies to all operating systems, but
by far most of the damage is done to/with Windows users due to its vast
popularity and many weaknesses.
(Note: Many people use terms like Trojan horse, virus, worm, hacking
and cracking all interchangeably, but they really don't mean the same thing. If
you're curious, here's a quick primer defining and distinguishing them. Let's
just say that once you are "infected", Trojans are just as dangerous as viruses
and can spread to hurt others just as easily!)
Methods of Activation
You can open a file by double clicking on it, but you can’t see the
behind process.
Most of the times these files can be .exe files which are in floppy
diskettes or in Compact Disks.
You might have down load something from the internet which you don’t
trust 100%.
You might open Email attachments without knowing.
Virus Effects
If your computer is running down slowly more than earlier. If the
machine shut downs abnormally. If you can see unknown files or folders have
been saved in to the hard disk. If anything abnormally happens in your machine
than earlier it might be to a virus effect.
Preventive Steps
1. Above all check every data medium you get. Even if it belongs to your best
friend, it does not give you the guarantee of security. It concerns not only
floppy disks, but also CD-ROMs, CD-RWs and ZIPs. Do not even open
floppy disk if you get it from an unknown person. Every data medium
obtained from an anonymous source is potentially infected.
2. Block the possibility of system boot from a floppy disk. Most of the latest
BIOSes have a function, which enables to do it. In that simple way you can
avoid the risk of having your computer infected by boot-sector viruses.
3. Do not open any letter with attached files received from an unknown
sender.
4. Do not run macros in documents of office packages if an anti-virus monitor
is off.
5. Use an anti-virus monitor working constantly at the background. For the
best security the monitor should check the incoming mail and every file
downloaded from the Internet.
6. You should systematically update definitions of viruses used by anti-virus
software. Updating should be done at least once a month (the best once a
week).
7. In a situation when you chat in the Internet (especially using mIRC) you
have to follow the same rules as in case of received e-mails. Do not open
any received files, if you do know who sent it to you and why. Some
viruses are sent automatically, so same information about sender does not
give you guarantee of security.
8. NEVER download blindly from people or sites which you aren't 100% sure
about. In other words, as the old saying goes, don't accept candy from
strangers. If you do a lot of file downloading, it's often just a matter of time
before you fall victim to a Trojan.
9. Even if the file comes from a friend, you still must be sure what the file is
before opening it, because many trojans will automatically try to spread
themselves to friends in an email address book or on an IRC channel. There
is seldom reason for a friend to send you a file that you didn't ask for. When
in doubt, ask them first, and scan the attachment with a fully updated anti-
virus program.
10. Beware of hidden file extensions! Windows by default hides the last
extension of a file, so that innocuous-looking "susie.jpg" might really be
"susie.jpg.exe" - an executable Trojan! To reduce the chances of being
tricked, unhide those pesky extensions.
11. NEVER use features in your programs that automatically get or preview
files. Those features may seem convenient, but they let anybody send you
anything which is extremely reckless. For example, never turn on "auto
DCC get" in mIRC, instead ALWAYS screen every single file you get
manually. Likewise, disable the preview mode in Outlook and other email
programs.
12. Never blindly type commands that others tell you to type, or go to web
addresses mentioned by strangers, or run pre-fabricated programs or scripts
(not even popular ones). If you do so, you potentially trust a stranger with
control over your computer, which can lead to Trojan infection or other
serious harm.
13. Don't be lulled into a false sense of security just because you run anti-virus
programs. Those do not protect perfectly against many viruses and trojans,
even when fully up to date. Anti-virus programs should not be your front
line of security, but instead they serve as a backup in case something sneaks
onto your computer.
14. Finally, don't download an executable program just to "check it out" - if it's
a Trojan, the first time you run it, you're already infected!
Introduction to Anti-virus Software
Antivirus (or "anti-virus") software is a class of program that searches
your hard drive and floppy disks for any known or potential viruses. The
market for this kind of program has expanded because of Internet growth and
the increasing use of the Internet by businesses concerned about protecting
their computer assets.
Following are some URLs where you can find more information about
antivirus software.
International Computer Security Association
http://www.icsa.net
Virus Bulletin
http://www.virusbtn.com
Dr Salomon's page
http://www.drsalomon.com
CERT - Computer Emergency Response Team
http://www.cert.org
McAfee anti-virus
http://vil.mcafee.com
Symantec
http://www.symantec.com/avcenter/
Other pages about virus:
http://www.mks.com.pl
http://www.antywirusy.pl
http://www.wirusy.pl
http://www.wirusy.onet.pl
http://www.viruslist.com
Norton
Antivirus software by Symantec that scans and cleans instant-message
attachments as well as email messages, and removes them automatically. You
can download 15 day trial version freely from the Symantec website.
McAfee
Anti-virus software by MacAfee Co. Scan and restores your PC
immediately. Detects Spy ware, blocks worms/unsafe scripts.
Virus Checking
Once you install the Virus guard it will automatically scan your system.
When you boot up the machine and until you shut down the system it will be
scanning your system behind other processes.
When you insert a unknown floppy diskette its better to scan the diskette
for viruses.
You can right click on the floppy drive and select scan for viruses or
open the anti virus program and select scan and then select floppy diskette.
Then it will remove the infected files from the particular files and if it is
not possible it asks to delete the infected files. It’s better to delete the infected
files permanently if the recovery is not possible.
Disinfection
Computer viruses can be stored on floppy disks, hard disks, and even in
the memory of a computer. Viruses frequently move from one computer to
another on floppy disks or via files attached to email messages.
Most viruses can be detected and removed using virus detection
software such as McAfee VirusScan. In Nebula, we configure this package to
be loaded at startup and watch for any signs of viruses. If Mc Afee VirusScan
detects a virus in a file you're working with, it will notify you and give you
some basic instructions on what to do next. You can also check the list below
for instructions on dealing with some of the more pervasive virus infections. If
you get a virus, you should always notify the person who gave you the file, by
telephone if possible, so they can get rid of it on their computer, too.
What you need to know
• Any email claiming to be a Microsoft update is actually a virus itself; delete
the file and do not click on any attachment(s).
• Any email from another person claiming that you have a virus is most
probably a virus hoax (see the Nebula virus hoax page for more
information).
• Do not delete files from your system based on an email message; check the
hoax page for more information.
• The most reliable source of information about a virus infection will come
from your computer's McAfee program. If this tells you that you have a
virus, do notify Nebula Support.
• Do not open unknown attachments, ever.
Immunization
Viruses remain a significant threat to modern networked computer
systems. Despite the best efforts of those who develop anti-virus systems, new
viruses and new types of virus that are not dealt with by existing protection
schemes appear regularly. In addition, the rate at which a virus can spread has
risen dramatically with the increase in connectivity. Defenses against infections
by known viruses rely at present on immunization yet, for a variety of reasons,
immunization is often only effective on a subset of the nodes in a network and
many nodes remain unprotected. Little is known about either the way in which
a viral infection proceeds in general or the way that immunization affects the
infection process. We present the results of a simulation study of the way in
which virus infections propagate through certain types of network and of the
effect that partial immunization has on the infection. The key result is that
relatively low levels of immunization can slow an infection significantly.
Removing
If you are not sure if your computer is virus-free, try removing a virus
from the hard disk as described below.
1. Shut down your machine, then start it up and log in; this ensures you have
the latest virus update files on your system.
2. Choose Start - Programs - Network Associates - Virus Scan to begin a virus
scan on your computer.
3. In the box labeled "Scan in", make sure the drive you wish to search for
viruses is selected, typically C: If it isn't, click "Browse" and choose the
right drive (and folder, if desired). Do not scan the I:\groups or H: drives;
they are scanned regularly by the engineers.
4. Note that the "Include subfolders" checkbox should be selected, so Virus
Scan looks through all subdirectories of the location you've chosen.
5. Note also that by default only program files are scanned; this includes Word
and Excel document files. If you wish to scan all files, click the "All files"
radio button.
6. Click "Scan Now" to start the search.
7. If a virus is found, click on the file name and choose Clean Infected Files.
8. If Virus Scan reports that it cannot clean a file, close the box and restart
your computer. Then repeat the scan. If Virus Scan repeats the report,
contact Nebula Support. If possible, use the Nebula Support icon on your
desktop; this will include other information about your system that may
help to solve the problem.
9. Remember, don't respond to an email telling you that you have a virus. It's
either a hoax (in which case you just get more spam now that they know
your address is valid), or a response to an infected message that only looks
like it came from you--the latest viruses disguise their "From" addresses.
Creation of a Rescue Disk
We can call rescue disk as a boot disk. Rescue disk or Boot disk can be
used in a situation where the computer does not boot in the normal way. This
abnormal condition is can be due to a virus effect.
You can follow the following instructions to create a boot disk in
Windows XP.
• Insert a 3 ½’ floppy diskette in to your machine.
• Double Click on My Computer Icon on the desktop.
• Right Click on Floppy Diskette Drive.
• Select Format
• Select Create MSDOS Startup Disk
• Click on Start to create the Disk.
Installing Anti-virus Software
To install the antivirus soft ware first you have to buy a CD or download it
from a website. As an example we’ll see how to install Norton Antivirus.
First you select the setup file and double click on it.
Then it will prompt you:
You have to click on Yes and then it will start to scan all the files in your
machine.
It will scan all the files and if there is any virus infected file it will show you.
When the scanning is complete it will show you a report.
Then the setup will continue to install the software.
After clicking Next button you have to read the software license agreement and
accept the agreement to proceed.
If you don’t accept the agreement setup will stop.
Then it will ask for the path of the destination folder where the software files
will be saved.
After selecting the correct path and folder it will show you where the software
will be installed. To proceed and install the software to your system you have
to click on the Next button.
Then you can see the progress of the installation.
After coping the installation files in to your hard drive it will show you the
Read me text file. The Readme.txt file contains the details about the product.
Click Next to proceed.
You will get this message if the setup has been successfully installed.
Click on Finish to finish installing the software.
After you install the software you have to register the product.
We are going to use the trial version. If you want you can purchase the product
online, or if you have already purchased you have to enter the product key
which you will receive after purchasing the original product.
Then it will display you a summary of tasks which the software will operate on.
You can do wanted modifications.
Click on Finish to finish the configuration.
Upgrading Anti-virus Software
Once you install the antivirus software it’s a must that you upgrade the
software frequently. You can do it online.
If your antivirus is not up to date then it will show you the following message.
After upgrading the automatic System Scan will run.
If you want you can stop the scan now and do it later.
After the scan it will give you a summary.
You can see whether the system scan is running in the background and its
configuration.
Uninstalling Anti-virus Software
If you feel that you need better antivirus software you can uninstall the current
antivirus software and install a new one.
We’ll see how to uninstall the current antivirus software.
You can go to the control panel and select Add/Remove Programs.
Then select Norton antivirus 2004 and click on Remove.
Then it will display:
You can click on Remove All.
Then it will warn you that this will remove antivirus software from your
system. You have to click on Next to proceed.
Then you can see the uninstallation progress.
After finishing the uninstallation it will ask to restart the machine.
You can select any option and click on Finish to finish the uninstallation.
PRIMARY STORAGEPRIMARY STORAGEPRIMARY STORAGEPRIMARY STORAGE
RAM
RAM (random access memory) is the place in a computer where the
operating system, application programs, and data in current use are kept so that
they can be quickly reached by the computer's processor. RAM is much faster
to read from and write to than the other kinds of storage in a computer, the hard
disk, floppy disk, and CD-ROM. However, the data in RAM stays
there only as long as your computer is running. When you
turn the computer off, RAM loses its data. When you
turn your computer on again, your operating system
and other files are once again loaded into RAM,
usually from your hard disk.
RAM can be compared to a person's short-term
memory and the hard disk to the long-term memory. The
short-term memory focuses on work at hand, but can
only keep so many facts in view at one time. If short-term memory fills up,
your brain sometimes is able to refresh it from facts stored in long-term
memory. A computer also works this way. If RAM fills up, the processor needs
to continually go to the hard disk to overlay old data in RAM with new,
slowing down the computer's operation. Unlike the hard disk which can
become completely full of data so that it won’t accept any more, RAM ever
runs out of memory. It keeps operating, but much more slowly than you may
want it to.
How Big is RAM?
RAM is small, both in physical size (it's stored in microchips) and in the
amount of data it can hold. It's much smaller than your hard disk. A typical
computer may come with 256 million bytes of RAM and a hard disk that can
hold 40 billion bytes. RAM
comes in the form of "discrete"
(meaning separate)
microchips and also in the form
of modules that plug into holes
in the computer's motherboard.
These holes connect through a bus or
set of electrical paths to the processor. The hard drive,
on the other hand, stores data on a magnetized
surface that looks like a phonograph record.
Most personal computers are designed to allow you to add additional
RAM modules up to a certain limit. Having more RAM in your computer
reduces the number of times that the computer processor has to read data in
from your hard disk, an operation that takes much longer than reading data
from RAM. (RAM access time is in nanoseconds; hard disk access time is in
milliseconds.)
Why Random Access?
RAM is called "random access" because any storage location can be
accessed directly. Originally, the term distinguished regular core memory from
offline memory, usually on magnetic tape in which an item of data could only
be accessed by starting from the beginning of the tape and finding an address
sequentially. Perhaps it should have been called "inconsequential memory"
because RAM access is hardly random.
RAM is organized and controlled in a way that enables data to be stored
and retrieved directly to specific locations. A term IBM has preferred is direct
access storage or memory. Note that other forms of storage such as the hard
disk and CDROM are also accessed directly (or "randomly") but the term
random access is not applied to these forms of storage.
In addition to disk, floppy disk, and CD-ROM storage, another
important form of storage is read-only memory (ROM), a more expensive kind
of memory that retains data even when the computer is turned off. Every
computer comes with a small amount of ROM that holds just enough
programming so that the operating system can be loaded into RAM each time
the computer is turned on.
ROM
ROM is "built-in" computer memory containing data that normally can
only be read, not written to. ROM contains the programming that allows your
computer to be "booted up" or regenerated each time you turn it on. Unlike a
computer's random access memory (RAM), the data in ROM is not lost when
the computer power is turned off. The ROM is sustained by a small long-life
battery in your computer. If you ever do the hardware setup procedure with
your computer, you effectively will be writing to ROM.
PROM
Programmable read-only memory (PROM) is read-only memory (ROM)
that can be modified once by a user. PROM is a way of allowing a user to tailor
a microcode program using a special machine called a PROM programmer.
This machine supplies an electrical current to specific cells in the ROM that
effectively blows a fuse in them. The process is known as burning the PROM.
Since this process leaves no margin for error, most ROM chips designed to be
modified by users use erasable programmable read-only memory (EPROM) or
electrically erasable programmable read-only memory (EEPROM).
EPROM
EPROM (erasable programmable read-only memory) is programmable
read-only memory (programmable ROM) that can be erased and re-used.
Erasure is caused by shining an intense ultraviolet light through a window that
is designed into the memory chip. (Although ordinary room lighting does not
contain enough ultraviolet light to cause erasure, bright sunlight can cause
erasure. For this reason, the window is usually covered with a label when not
installed in the computer.)
A different approach to a modifiable ROM is electrically erasable
programmable read-only memory (EEPROM).
EEPROM
EEPROM (electrically erasable programmable read-only memory) is
user-modifiable read-only memory (ROM) that can be erased and
reprogrammed (written to) repeatedly through the application of higher than
normal electrical voltage. Unlike EPROM chips, EEPROMs do not need to be
removed from the computer to be modified. However, an EEPROM chip has to
be erased and reprogrammed in its entirety, not selectively. It also has a limited
life - that is, the number of times it can be reprogrammed is limited to tens or
hundreds of thousands of times. In an EEPROM that is frequently
reprogrammed while the computer is in use, the life of the EEPROM can be an
important design consideration. A special form of EEPROM is flash memory,
which uses normal PC voltages for erasure and reprogramming.
Cache
A cache (pronounced CASH) is a place to store something temporarily.
The files you automatically request by looking at a Web page are stored on
your hard disk in a cache subdirectory under the directory for your browser (for
example, Internet Explorer). When you return to a page you've recently looked
at, the browser can get it from the cache rather than the original server, saving
you time and the network the burden of some additional traffic. You can
usually vary the size of your cache, depending on your particular browser.
Computers include caches at several levels of operation, including cache
memory and a disk cache. Caching can also be implemented for Internet
content by distributing it to multiple servers that are periodically refreshed.
(The use of the term in this context is closely related to the general concept of a
distributed information base.)
Altogether, we are aware of these types of caches:
• International, national, regional, organizational and other "macro"
caches to which highly popular information can be distributed and
periodically updated and from which most users would obtain
information.
• Local server caches (for example, corporate LAN servers or access
provider servers that cache frequently accessed files). This is similar to
the previous idea, except that the decision of what data to cache may be
entirely local.
• Your Web browser's cache, which contains the most recent Web files
that you have downloaded and which is physically located on your hard
disk (and possibly some of the following caches at any moment in time)
• A disk cache (either a reserved area of RAM or a special hard disk
cache) where a copy of the most recently accessed data and adjacent
(most likely to be accessed) data is stored for fast access.
• RAM itself, which can be viewed as a cache for data that is initially
loaded in from the hard disk (or other I/O storage systems).
• L2 cache memory, which is on a separate chip from the microprocessor
but faster to access than regular RAM.
• L1 cache memory on the same chip as the microprocessor.
SECONDARY STORAGESECONDARY STORAGESECONDARY STORAGESECONDARY STORAGE
Secondary storage is all addressable data storage that is not currently in
the computer's main storage or memory. Synonyms are external storage and
auxiliary storage.
Floppy Disks
A diskette is a random access, removable data storage medium that can
be used with personal computers. The term usually refers to the magnetic
medium housed in a rigid plastic cartridge measuring 3.5 inches square
and about 2 millimeters thick. Also called a
"3.5-inch diskette," it can store up to 1.44
megabytes (MB) of data. Although many
personal computers today come with a 3.5-
inch diskette drive preinstalled, some
notebook computers and centrally-
administered desktop computers omit them.
Some older computers provide drives for magnetic diskettes
that are 5.25 inches square, about 1 millimeter thick, and capable of holding 1.2
megabytes of data. These were sometimes called "floppy disks" or "floppies"
because their housings are flexible. In recent years, 5.25-inch diskettes have
been largely replaced by 3.5-inch diskettes, which are physically more rugged.
Many people also call the newer hard cased diskette a "floppy." Magnetic
diskettes are convenient for storing individual files and small programs.
However, the magneto-optical (MO) disk is more popular for mass storage,
backup, and archiving. An MO diskette is only a little larger, physically, than a
conventional 3.5-inch magnetic diskette. But because of the sophisticated
read/write technology, the MO diskette can store many times more data.
Disk Drives
Hard Disks
A hard disk is part of a unit, often called a "disk drive," "hard drive," or
"hard disk drive," that store and provides relatively quick access to large
amounts of data on an electromagnetically charged surface or set of surfaces.
Today's computers typically come with a hard disk that contains several billion
bytes (gigabytes) of storage.
A hard disk is really a set of stacked "disks," each of which, like
phonograph records, has data recorded electromagnetically in concentric circles
or "tracks" on the disk. A "head" (something like a phonograph arm but in a
relatively fixed position) records (writes) or reads the information on the tracks.
Two heads, one on each side of a disk, read or write the data as the disk spins.
Each read or write operation requires that data be located, which is an operation
called a "seek." (Data already in a disk cache, however, will be located more
quickly.)
A hard disk/drive unit comes with a set rotation speed varying from
4500 to 7200 rpm. Disk access time is measured in milliseconds. Although the
physical location can be identified with cylinder, track, and sector locations,
these are actually mapped to a logical block address (LBA) that works with the
larger address range on today's hard disks.
Top view of a 36 GB, 10,000 RPM, IBM SCSI server hard disk, with its top
cover removed. Note the height of the drive and the 10 stacked platters. (The
IBM Ultra star 36ZX.)
Optical Disks
An optical disc is an electronic data storage medium that can be written
to and read using a low-powered laser beam. Originally developed in the late
1960s, the first optical disc, created by James T. Russell,
stored data as micron-wide dots of light and dark.
A laser read the dots, and the data was converted to
an electrical signal, and finally to audio or visual
output. However, the technology didn't appear in
the marketplace until Philips and Sony came out with the compact
disc (CD) in 1982. Since then, there has been a constant succession of optical
disc formats, first in CD formats, followed by a number of DVD formats.
Optical disc offers a number of advantages over magnetic storage media.
An optical disc holds much more data. The greater control and focus possible
with laser beams (in comparison to tiny magnetic
heads) means that more data can be written into a
smaller space. Storage capacity increases with
each new generation of optical media.
Emerging standards, such as Blu-ray, offer up
to 27 gigabytes (GB) on a single-sided 12-
centimeter disc. In comparison, a diskette, for
example, can hold 1.44 megabytes (MB). Optical discs are inexpensive to
manufacture and data stored on them is relatively impervious to most
environmental threats, such as power surges, or magnetic disturbances.
CD-ROM
CD-ROM (Compact Disc, read-only-memory) is an adaptation of the
CD that is designed to store computer data in the form of text and graphics, as
well as hi-fi stereo sound. The original data format standard
was defined by Philips and Sony in the 1983 Yellow
Book. Other standards are used in conjunction
with it to define directory and file
structures, including ISO 9660, HFS
(Hierarchal File System, for Macintosh
computers), and Hybrid HFS-ISO. Format of the
CD-ROM is the same as for audio CDs: a standard CD is 120 mm
(4.75 inches) in diameter and 1.2 mm (0.05 inches) thick and is composed of a
polycarbonate plastic substrate (under layer – this is the main body of the disc),
one or more thin reflective metal (usually aluminum) layers, and a lacquer
coating.
The Yellow Book specifications were so general that there was some
fear in the industry that multiple incompatible and proprietary formats would
be created. In order to prevent such an occurrence, representatives from
industry leaders met at the High Sierra Hotel in Lake Tahoe to collaborate on a
common standard. Nicknamed the High Sierra Format, this version was later
modified to become ISO 9660. Today, CD-ROMs are standardized and will
work in any standard CD-ROM drive. CD-ROM drives can also read audio
compact discs for music, although CD players cannot read CD-ROM discs.
CD-ROM Data Storage
Although the disc media and the drives of the CD and CD-ROM are, in
principle, the same, there is a difference in the way data storage is organized.
Two new sectors were defined, Mode 1 for storing computer data and Mode 2
for compressed audio or video/graphic data.
CD-ROM Mode 1
CD-ROM Mode 1 is the mode used for CD-ROMs that carry data and
applications only. In order to access the thousands of data files that may be
present on this type of CD, precise addressing is necessary. Data is laid out in
nearly the same way as it is on audio disks: data is stored in sectors (the
smallest separately addressable block of information), which each hold 2,352
bytes of data, with an additional number of bytes used for error detection and
correction, as well as control structures. For mode 1 CD-ROM data storage, the
sectors are further broken down, and 2,048 used for the expected data, while
the other 304 bytes are devoted to extra error detection and correction code,
because CD-ROMs are not as fault tolerant as audio CDs. There are 75 sectors
per second on the disk, which yields a disc capacity of 681,984,000 bytes
(650MB) and a single speed transfer rate of 150 kbps, with higher rates for
faster CD-ROM drives. Drive speed is expressed as multiples of the single
speed transfer rate, as 2X, 4X, 6X, and so on. Most drives support CD-ROM
XA (Extended Architecture) and Photo-CD (including multiple session discs).
CD-ROM Mode 2
CD-ROM Mode 2 is used for compressed audio/video information and uses
only two layers of error detection and correction, the same as the CD-DA.
Therefore, all 2,336 bytes of data behind the sync and header bytes are for user
data. Although the sectors of CD-DA, CD-ROM Mode 1 and Mode 2 are the
same size, the amount of data that can be stored varies considerably because of
the use of sync and header bytes, error correction and detection. The Mode 2
format offers a flexible method for storing graphics and video. It allows
different kinds of data to be mixed together, and became the basis for CD-
ROM XA. Mode 2 can be read by normal CD-ROM drives, in conjunction with
the appropriate drivers.
Data Encoding and Reading
The CD-ROM, like other CD adaptations, has data encoded in a spiral track
beginning at the center and ending at the outermost edge of the disc. The spiral
track holds approximately 650 MB of data. That's about 5.5 billion bits. The
distance between two rows of pits, measured from the center of one track to the
center of the next track is referred to as track pitch. The track pitch can range
from 1.5 to 1.7 microns, but in most cases is 1.6 microns.
Constant Linear Velocity (CLV) is the principle by which data is read from a
CDROM. This principal states that the read head must interact with the data
track at a constant rate, whether it is accessing data from the inner or outermost
portions of the disc. This is affected by varying the rotation speed of the disc,
from 500 rpm at the center, to 200 rpm at the outside. In a music CD, data is
read sequentially, so rotation speed is not an issue. The CD-ROM, on the other
hand, must read in random patterns, which necessitates constantly shifting
rotation speeds. Pauses in the read function are audible, and some of the faster
drives can be quite noisy because of it.
Magnetic Tape
The use of magnetic media to record and store numeric and textual
information, sound, motion, and still images has presented librarians and
archivists with opportunities and challenges. On the one hand, magnetic media
increase the kinds of artifacts and events we can capture and store. On the other
hand, their special long-term storage needs are different from traditional library
materials, confusing to those in charge of their care, and demanding of
resources not always available to libraries and archives. Audio and video
collections require specific care and handling to ensure that the recorded
information will be preserved. Special storage environments may be required if
the recorded information is to be preserved for longer than ten years. For
information that must be preserved indefinitely, periodic transcription from old
media to new media will be necessary, not only because the media are unstable,
but because the recording technology will become obsolete. As an information
storage medium, magnetic tape is not as stable as film or paper. Properly cared
for, film and nonacid paper can last for centuries, whereas magnetic tape will
only last a few decades. Use of magnetic media for storage is further
confounded by the prevalence of several formats (e.g., U-mastic, VHS, S-VHS,
8mm, and Beta Cam for video), media types (iron oxide, chromium dioxide,
barium ferrite, metal particulate, and metal evaporated), and by rapid advances
in media technology. On the other hand, books have virtually maintained the
same format for centuries, have almost exclusively used ink on paper as the
information storage medium, and require no special technology to access the
recorded information. Likewise, newer microfilm, microfiche, and movie film
are known for their stability when kept in proper environments, and viewing
formats have not changed significantly over the years. (The breakdown of
acetate backing that plagues older film materials is discussed in Section 2.3:
Substrate Deformation.) This report will compare care and handling procedures
for tapes with procedures for paper and film whenever possible.
Zip Drives
A Zip drive is a small, portable disk drive used primarily for backing up and
archiving personal computer files. The trademarked Zip drive was developed
and is sold by Iomega Corporation. Zip drives and disks come in two sizes. The
100 megabyte size actually holds 100,431,872 bytes of data or the equivalent of
70 floppy diskettes. There is also a 250 megabyte drive and disk. The Iomega
Zip drive comes with a software utility that lets you copy the entire contents of
your hard drive to one or more Zip disks.
In addition to data backup, Iomega suggests these additional uses:
• Archiving old e-mail or other files you don't use any more but may want
to access someday
• Storing unusually large files, such as graphic images that you need
infrequently
• Exchanging large files with someone
• Putting your system on another computer, perhaps a portable computer
• Keeping certain files separate from files on your hard disk (for example,
personal finance files)
The Zip drive can be purchased in either a parallel or a Small Computer System
Interface (SCSI) version. In the parallel version, a printer can be chained off
the Zip drive so that both can be plugged into your computer's parallel port.
DVD
DVD (digital versatile disc) is an optical disc technology that is expected to
rapidly replace the CD-ROM disc (as well as the audio compact disc) over the
next few years. The digital versatile disc (DVD) holds 4.7 gigabyte of
information on one of its two sides, or enough for a 133-minute movie. With
two layers on each of its two sides, it will hold up to 17 gigabytes of video,
audio, or other information. (Compare this to the current CD-ROM disc of the
same physical size, holding 600 megabyte. The DVD can hold more than 28
times as much information!) DVD-Video is the usual name for the DVD format
designed for full-length movies and is a box that will work with your television
set. DVD-ROM is the name of the player that will (sooner or later) replace
your computer's CD-ROM. It will play regular CDROM discs as well as DVD-
ROM discs. DVD-RAM is the writeable version. DVD Audio is a player
designed to replace your compact disc player. DVD uses the MPEG-2 file and
compression standard. MPEG-2 images have four times the resolution of
MPEG-1 images and can be delivered at 60 interlaced fields per second where
two fields constitute one image frame. (MPEG-1 can deliver 30 nonintegrated
frames per second.) Audio quality on DVD is comparable to that of current
audio compact discs.
NETWORKNETWORKNETWORKNETWORKSSSS
Introduction
After learning the section you will be able to describe Communication,
Data Communications, Data Transmission, Networks, and different Hardware
and software used to communicate between computers effectively.
Computer Network and Usage
A network is a collection of computers and devices connected by
communications channels that facilitates communications among users and
allows users to share resources with other users. Some examples of resources
are data, information, hard ware, and software. The following paragraphs
explain the advantages of using a network.
Facilitating Communications
Using a network, people can communicate efficiently and easily via e-
mail, instant messaging, chat rooms, telephony, video telephone calls, and
videoconferencing. Sometimes these communications occur within a business’s
network. Other times, they occur globally through the Internet. As discussed
earlier in this chapter, users have a multitude of devices available to send and
receive communications.
Sharing Hardware
In a networked environment, each computer on a network can access
and use hardware on the network. Suppose several personal computers on a
network each require the use of a laser printer. If the personal computers and a
laser printer are connected to a network, the personal computer users each can
access the laser printer on the network, as they need it. Business and home
users network their hardware for one main reason. That is, it may be too costly
to provide each user with the same piece of hardware such as a printer.
Sharing Data and Information
In a networked environment, any authorized computer user can access
data and information stored on other computers on the network. A large
company, for example, might have a database of customer information. Any
authorized per son, including a mobile user using a handheld computer to
connect to the network, can access this database. The capability of providing
access to and storage of data and information on shared storage devices is an
important feature of many networks.
Sharing Software
Users connected to a network can access software (programs) on the
network. To support multiple user access of software, most software vendors
sell network versions of their software. In this case, software vendors issue a
site license. A site license is a legal agreement that allows multiple users to run
the software package simultaneously. The site license fee usually is based on
the number of users or the number of computers attached to the network.
Sharing software via a network usually costs less than buying individual copies
of the software package for each computer.
Many mobile users today access their company networks through a
virtual private network. When a mobile user connects to a main office using the
Internet, a virtual private network (VPN) provides the mobile user with a
secure connection to the company network server, as if the user had a private
line. VPNs help to ensure that transmitted data is safe from being intercepted
by unauthorized people.
Problems Associated with Standalone Computers
� Sharing Hardware devices such as printers, scanners and Hard Disks.
� Difficulties in sharing software.
� Difficulties in sharing data and Information.
� Storage problems.
� Difficulties of communication between computers.
Introduction
Computers were stand-alone devices when first introduced. As they
became more widely used, manufacturers designed hardware and software so
one computer could communicate with another. Computer communications
describes a process in which one computer transfers data, instructions, and
information to another computer(s). Originally, only large computers had
communications capabilities. Today, even the smallest computers and devices
can communicate with one another. The Internet provides a means for
worldwide communications.
What is a Communication?
The following picture shows a sample communications system. As
illustrated in this figure, communications systems contain all types of devices.
An example of a communications system. Some devices that can serve
as sending and receiving devices are
a) Personal computers
b) Notebook computers
c) Web enabled cellular telephones
d) Web-enabled handheld computers
e) MSN TV
f) GPS receivers
The communications channel consists of telephone lines, underground
cables, microwave stations, and satellites. The primary function of a
communications device, such as a modem, is to convert or format signals so
they are suitable for the communications channel or a receiving device. When
using a telephone line as the communications channel, you need a modem to
convert between analog and digital signals. An analog signal consists of a
continuous electrical wave. Computers, however, process data as digital
signals. A digital signal consists of individual electrical pulses that represent
the bits grouped together into bytes.
For instance, a modem connected to a sending computer converts the
computer’s digital signals into analog signals. The analog signals then travel
over a communications channel, such as a standard telephone line. At the
receiving end, another modem converts the analog signals back into digital
signals that a receiving computer can recognize.
Sending and Receiving Devices
Sending and receiving devices initiate or accept transmission of data,
instructions, and information. Notebook computers, desktop computers, mid-
range servers, and main frame computers all can serve as sending and receiving
devices. These computers can communicate directly with another computer,
with hundreds of computers on a company network, or with millions of other
computers on the Internet.
A modem converts the individual electrical pulses of a digital signal into
analog signals for data transmission over some telephone lines. At the receiving
computer, another modem converts the analog signals back into digital signals
that the computer can process.
Basic Requirements for Successful Communications
For successful communications, you need the following:
� A sending device that initiates an instruction to transmit data,
instructions, or information.
� A communications device that converts or formats the data, instructions,
or information from the sending device into signals carried by a
communications channel.
� A communications channel, or path, on which the signals travel.
� A communications device that receives the signals from the
communications channel and converts or formats them so the receiving
device can recognize the signals.
� A receiving device that accepts the transmission of data, instructions, or
information.
Communication Types
Simplex Communication
Simplex data communication specifies that communication on a given
channel can only flow in one direction. In this environment, only one entity is
allowed to transmit and all others act as receivers. It should be noted that the
sending device cannot receive data and the receiving entity cannot transmit
data. Perhaps a good analogy of this type of communication would be your
local radio station. The radio station broadcasts a message (the transmitting
device) and you receive the message on your radio (the receiving device). This
represents a one-way communication stream. Simplex Communication Data
transfer in one direction only.
Half-Duplex Communication
Unlike simplex communication, half-duplex communication allows each
device to send and receive data, but only one device at a time can transmit. A
key point is that when you are transmitting the entire channel is being used for
that purpose. You cannot receive and transmit at the same time. The best
example of this would be a child’s walkie-talkie. You push a button to talk and
release it to receive. It can best be stated by saying half- duplex provides for bi-
directional communication, but only in one direction at a time.
Half-Duplex Communication Data transfer both directions but only one
direction at a time.
Full-Duplex Communication
Full-duplex communication provides for two-way communicate at the
same time. An everyday example of full-duplex communication would be your
basic telephone system. Unlike the walkie-talkies (half duplex), full-duplex
communication allows both parties to transmit and receive at the same time.
Full-Duplex Communication Data transfer both directions at the same
time.
Data Communication
Analog Signal
In telecommunications, an analog signal is one in which a base carrier's
alternating current frequency is modified in some way, such as by amplifying
the strength of the signal or varying the frequency, in order to add information
to the signal. Broadcast and telephone transmission have conventionally used
analog technology.
An analog signal can be represented as a series of sine waves. The term
originated because the modulation of the carrier wave is analogous to the
fluctuations of the human voice or other sound that is being transmitted.
Analog describes any fluctuating, evolving, or continually changing
process.
Digital Signal
Digital describes electronic technology that generates, stores, and
processes data in terms of two states: positive and non-positive. Positive is
expressed or represented by the number 1 and non-positive by the number 0.
Thus, data transmitted or stored with digital technology is expressed as a string
of 0's and 1's. Each of these state digits is referred to as a bit (and a string of
bits that a computer can address individually as a group is a byte).
Prior to digital technology, electronic transmission was limited to analog
technology, which conveys data as electronic signals of varying frequency or
amplitude that are added to carrier waves of a given frequency. Broadcast and
phone transmission has conventionally used analog technology.
Digital technology is primarily used with new physical communications
media, such as satellite and fiber optic transmission. A modem is used to
convert the digital information in your computer to analog signals for your
phone line and to convert analog phone signals to digital information for your
computer.
Types of Transmission Media
Transmission Media, Network Cables and Connectors
Perhaps the most important network components are the media and
connectors used to attach computers to the system. The word “media” simply
refers to the physical pathway on which network data travels. In most cases,
this media is some type of cable. We refer to these cables as bounded media.
Within the networking environment, many different types of bounded media
are used. Each of these has very different characteristics such as speed,
maximum length and connection types. The following is a list of the most
common type of cables:
Cable media
Coaxial cable, Unshielded twisted pair cable, Shielded twisted pair
cable, Fiber optic cable.
Wireless media
Radio Frequency, Infrared, Microwave.
Twisted Pair
Twisted pair cable consists of at least two insulated wires twisted
together to reduce the effects of crosstalk. There are two broad categories of
twisted pair cables. They are UTP (unshielded twisted pair cable) and STP
(shielded twisted pair cable).
STP (Shielded Twisted Pair) cable is very resistant to environmental
factors like EMI because of the added layer of shielding that surrounds the
twisted wires. STP cable tends to be more expensive than UTP and is also
harder to work with than the thinner unshielded variety. The most common
implementation of STP is for IBM Token ring cables.
UTP (Shielded Twisted Pair), as the name would imply, does not have
an added layer of shielding and is therefore thinner and cheaper to
manufacture. UTP cable is rated in categories: Category 3 and 5 are the most
common for data grade transmissions. The CAT 3 cable was dominant in the
early years of networking but has been replaced by CAT 5 wiring because.
CAT 5 is better able to create a stable platform for data transmissions greater
than 10 Mbps. The CAT 5 twisted pair cable can support speeds of 100 Mbps.
The main physical difference between CAT 3 and CAT 5 cable is the number
of twists per inch. The CAT 5 cable has many more twists than CAT 3,
eliminating most crosstalk. UTP cable closely resembles the cable used by
telephones in your home.
Coaxial Cable
Coaxial cable, typically called coax cable, uses a center core conductor
that is insulated and surrounded by either a braided or solid thin foil aluminum
shield. Coax cable is very similar in appearance to the type used by television
cable companies in your home.
However, it should be noted that these are not the same and can not be
interchanged. Due to the amount of shielding, coax cable is very resistant to
crosstalk (interference from adjacent wires) and EMI (electromagnetic
interference). The graphic below shows that a coax cable is composed of an
outer jacket, an outer shield, an insulator and the center conductor.
Fiber Optic
Fiber optic cable uses a small strand of glass or plastic, instead of
copper, as the core of the cable. It consists of a glass center core surrounded by
a plastic sheath and a layer of gel or wire stands. Fiber optic cable offers a
major advantage over copper wire. It is almost completely immune to EMI and
does not suffer from attenuation (loss of signal strength over distance) like
copper cable. Fiber cable tends to be very expensive as compared to copper
wire. However, this cost variance should decrease as more companies choose
to implement this technology.
Advantages over copper-based media:
� Supports greater distances (up to 4 kilometers)
� Immune to EMI (Electromagnetic Interference)
� Immune to RFI (Radio Frequency Interference)
� Disadvantages of Fiber-Optic Cable:
� More expensive than copper-based media
� Difficult to install and support.
Wireless Media
After discussing coaxial, twisted pair and fiber optic cable, one might
get the impression that these are the only media options available. Copper and
fiber optic cabling are by far the most prevalent implementations. However,
there is another option that is gaining more acceptances in the networking
world. This option is wireless media. Wireless technology is not new. In fact,
the technology has been around for many years. This technology allows
computers fitted with special wireless adapters (NICs) to communicate with
other network devices, computers, printers, etc. without the use of cables.
To date, wireless networks have been limited mostly to smaller
workgroup environments supporting only a limited number of computers and
peripheral devices. These wireless networks can also become part of a larger
cabled network using special wireless ports called access points. The access
point is actually a device that converts the wireless signal to a signal that can be
placed on a cabled network. These devices can be dedicated access points or
simply a computer equipped with both a wireless adapter and a conventional
NIC, which is connected to the larger network via copper or fiber optic cable.
There are basically two different types of technology used in wireless
communications, RF (Radio Frequencies) and infrared technology. Of the two,
infrared technology is the one most often implemented in workgroup
environments. Whether using RF or infrared technologies, environmental
conditions and distance factors will have a significant influence on the
performance expectations of the network. The typical wireless access point can
normally support up to about twenty computers within a 30 to 60 meter radius.
This is would be under ideal conditions. Other factors, such as
intervening walls and environmental conditions, may reduce performance and
distance even further.
Radio frequency
Radio frequency (abbreviated RF, rf, or r.f.) is a term that refers to
alternating current (AC) having characteristics such that, if the current is input
to an antenna, an electromagnetic (EM) field is generated suitable for wireless
broadcasting and/or communications. These frequencies cover a significant
portion of the electromagnetic radiation spectrum, extending from nine
kilohertz (9 kHz), the lowest allocated wireless communications frequency (it's
within the range of human hearing), to thousands of gigahertz (GHz).
Transmission of Digital Data
A modem modulates outgoing digital signals from a computer or other
digital device to analog signals for a conventional copper twisted pair
telephone line and demodulates the incoming analog signal and converts it to a
digital signal for the digital device.
In recent years, the 2400 bits per second modem that could carry e-mail
has become obsolete. 14.4 Kbps and 28.8 Kbps modems were temporary
landing places on the way to the much higher bandwidth devices and carriers of
tomorrow. From early 1998, most new personal computers came with 56 Kbps
modems. By comparison, using a digital Integrated Services Digital Network
adapter instead of a conventional modem, the same telephone wire can now
carry up to 128 Kbps. With Digital Subscriber Line (DSL) systems, now being
deployed in a number of communities, bandwidth on twisted-pair can be in the
megabit range.
Information Networks
LAN
A local area network (LAN) is a group of computers and associated
devices that share a common communications line or wireless link and
typically share the resources of a single processor or server within a small
geographic area (for example, within an office building). Usually, the server
has applications and data storage that are shared in common by multiple
computer users. A local area network may serve as few as two or three users
(for example, in a home network) or as many as thousands of users (for
example, in an FDDI network).
MAN
A metropolitan area network (MAN) is a network that interconnects
users with computer resources in a geographic area or region larger than that
covered by even a large local area network (LAN) but smaller than the area
covered by a wide area network (WAN).
The term is applied to the interconnection of networks in a city into a
single larger network (which may then also offer efficient connection to a wide
area network). It is also used to mean the interconnection of several local area
networks by bridging them with backbone lines. The latter usage is also
sometimes referred to as a campus network.
Examples of metropolitan area networks of various sizes can be found in
the metropolitan areas of London, England; Lodz, Poland; and Geneva,
Switzerland. Large universities also sometimes use the term to describe their
networks. A recent trend is the installation of wireless MANs.
WAN
A wide area network (WAN) is a geographically dispersed
telecommunications network. The term distinguishes a broader
telecommunication structure from a local area network. A wide area network
may be privately owned or rented, but the term usually connotes the inclusion
of public (shared user) networks. An intermediate form of network in terms of
geography is a metropolitan area network (MAN).
Network Topology
Network topology refers to how your network is wired (the physical
configuration). Choosing the right configuration (topology) for a given
situation can directly affect a network’s speed, its flexibility to expand and just
how robust or fault- tolerant it is. There are many choices for designing a
network topology. The most common choices are:
1. Bus
2. Star
3. Ring
4. Mesh
5. Hybrid
It should be noted that there are many variations and hybrids of the
above topologies. These topologies can exist separately or in a mixed
environment. It should be stressed that a mixture of topologies is much harder
to administrate and more difficult to troubleshoot.
Bus
The basic bus topology is relatively easy to install and requires the least
amount of media (cable) as compared to the other topologies. Every computer
or device is connected to the next in a daisy-chain fashion. The first and last
device on the chain must be terminated with a resistor that matches the
impedance of cable that you are using. While the bus topology is fairly easy to
install, it can be one of the most difficult to troubleshoot. Another major
limitation of a bus topology is that a cable fault or break anywhere down the
length of the cable will affect all computers on that segment. The graphic
below depicts an example of a bus topology. One very common
implementation of the bus topology is Apple’s Local Talk, which is a
proprietary Data Link layer implementation developed by Apple Computer for
its AppleTalk protocol suite. Local Talk was designed as a cost-effective
network solution for connecting local workgroups. Local Talk hardware
typically is built into Apple products, which are easily connected by using
inexpensive twisted-pair cabling. Local Talk networks are almost always
organized in a bus topology.
A Diagram of a Bus Topology
Star
The most important distinction between the bus topology and the star
topology is that a star topology offers a much higher degree of redundancy.
Unlike the bus topology where one fault could bring Dow n the entire network,
the star connects each computer with its own dedicated cable. A failure of one
cable will affect only that machine. A star topology also tends to be much more
flexible if you have to move or reconfigure computers. The cost of this
topology is somewhat higher with the added expense of using a hub or
concentrator. However this cost is more than justified if you ever have the need
to troubleshoot the cable plant. The example below depicts a star topology.
A Diagram of a Star Topology
Ring
A ring topology is made up of computers that are connected in a circular
configuration. Each computer or device in the ring is connected to two others.
Data in this configuration travels around the ring in one direction and each
device in the ring can also act as repeater to boost the signal if necessary. A
ring topology generally uses more cable than either the bus or the star. A ring
topology is shown below.
A Diagram of a Ring Topology
Hybrid
A combination of any two or more network topologies. Note 1:
Instances can occur where two basic network topologies, when connected
together, can still retain the basic network character, and therefore not be a
hybrid network. For example, a tree network connected to a tree network is still
a tree network. Therefore, a hybrid network accrues only when two basic
networks are connected and the resulting network topology fails to meet one of
the basic topology definitions. For example, two star networks connected
together exhibit hybrid network topologies. Note 2: A hybrid topology always
accrues when two different basic network topologies are connected.
A Diagram of a Hybrid Topology
Mesh
The mesh topology is by far the most redundant of all of the topologies
mention so far. However, this does come with an added expense. The mesh
topology requires much more cable than any of the other topologies. In a true
mesh topology, every device is directly connected to every other device. It is
this configuration that makes it so redundant. However, if there ever is a
problem, it can be very difficult to locate the offending cable. The example
below depicts a mesh topology.
A Diagram of a Mesh Topology
Network Operating Systems
A Network Operating System (NOS) is a specific kind of program
designed to allow users to share resources over a computer network. These
resources may include other programs and files as well as printers and other
hardware. The Network Operating System sets the rules for this sharing of
resources and allows a variety of kinds of computers and components to
communicate. The most significant Network Operating Systems today are
Microsoft’s Windows NT and Windows 2000, Novell NetWare and the
different versions of UNIX and Linux.
Client/Server Networking
One concept that is important in our discussion of Operating Systems is
the concept of client/server networking. In this section, we will focus on the
server side of networking. In an o future section we will turn our focus to the
client side.
Servers
In a client/server networking environment, certain systems are set up as
servers, which means that they serve resources to other systems. Servers can
provide various functions. For example, a server might be set up as a print
server in order to manage the printing on a network. Or a server might play the
role of a file server, hosting files on a network so that users can share and
access files were the network. Servers may also act as application servers to
host applications that are used on the network. Another important role that is
frequently performed by servers is to control security on the network to ensure
that only authorized users are able to access network resources. It is important
to note that typically servers are the bigger, faster machines on the network and
are often dedicated servers that perform very specific functions. There are
instances, however, when a server may act as both a server and a client.
Clients
Very simply, clients are the systems on the network that request and
access information from the servers. These are the systems that end users sit at
to perform their work. Another term that is used almost interchangeably with
client is workstation.
OSI Model
In response to the need for networking standards, various industry
organizations attempted to create models. Most of these models dealt with the
issues of moving information or data from one location to another. The work of
these various industry organizations laid the groundwork for what was to
become the most widely accepted model for networking, the OSI (Open
Systems Interconnection) model. In about 1977, the ISO (International
Organization for Standards) adopted a mandate to develop a set of standards
that would address the issues of interoperability in a multivendor environment.
The fruits of their labor became the OSI model.
The OSI model subdivides the intricacies of networking into seven
separate parts:
1. Application
2. Presentation
3. Session
4. Transport
5. Network
6. Data link
7. Physical
It is important to keep in mind that the OSI model is a design or
blueprint for how communication should occur. It attempts to divide the
otherwise complicated task of communication between devices into logical sub
groups called layers. This process is somewhat akin to the task of building a
house. Viewing this process as a whole can be quite overwhelming. However,
most houses are built by subcontractors, each specializing in a particular area.
This is exactly what the OSI model does for networking, creating individual
layers at which software and hardware vendors can function. This means, for
example, that a manufacturer of network interface cards needs only to be
familiar with standards set by the lower layers of the OSI model, while a
software vendor of a terminal emulation program might be concerned only with
the upper few layers of the model.
What is a Protocol?
When data is being transmitted between two or more devices something
needs to govern the controls that keep this data intact. A formal description of
message formats and the rules two computers must follow to exchange those
messages. Protocols can describe low-level details of machine-to-machine
interfaces (e.g., the order in which hits and bytes are sent across wire) or high-
level exchanges between application programs (e.g., the way in which two
programs transfer a file across the Internet)
TCP/IP
TCP
The main function of TCP is to establish and monitor connections
between the sending and receiving devices. TCP is responsible for providing
reliable connection-oriented data delivery. TCP functions at the Transport layer
of the OSI model. When you are using TCP, you basically have an
acknowledgement between sender and receiver that is maintained the entire
length of the data transmission.
IP
Internet Protocol provides the mechanism for Internet addressing. IP
functions at the Network layer of the OSI model. There are basically two parts
to an IP address; the first part defines the network a device is attached to, and
the second portion identifies the actual device itself. An IP address can be
assigned by the network administrator or assigned by a DHCP (Dynamic Host
Configuration Protocol) server.
NetBEUI
NetBEUI (NetBIOS Extended User Interface) is a new, extended
version of NetBIOS, the program that lets computers communicates within a
local area network. NetBEUI (pronounced net-BOO-ee) formalizes the frame
format (or arrangement of information in a data transmission) that was not
specified as part of NetBIOS. NetBEUI was developed by IBM for its LAN
Manager product and has been adopted by Microsoft for its Windows NT,
LAN Manager, and Windows for Workgroups products. Hewlett-Packard and
DEC use it in comparable products. NetBEUI is the best performance choice
for communication within a single LAN. Because, like NetBIOS, it does not
support the routing of messages to other networks, its interface must be adapted
to other protocols such as Internet work Packet Exchange or TCP/IP. A
recommended method is to install both NetBEUI and TCP/IP in each computer
and set the server up to use NetBEUI for communication within the LAN and
TCP/IP for communication beyond the LAN.
IPX/SPX
IPX (Internet work Packet Exchange) is a networking protocol from
Novell that interconnects networks that use Novell's NetWare clients and
servers. IPX is a datagram or packet protocol. IPX works at the Network layer
of communication protocols and is connectionless (that is, it doesn't require that
a connection be maintained during an exchange of packets as, for example, a
regular voice phone call does).
Packet acknowledgment is managed by another Novell protocol, the
Sequenced Packet Exchange (SPX). Other related Novell NetWare protocols
are: the Routing Information Protocol (RIP), the Service Advertising Protocol
(SAP), and the NetWare Link Services Protocol (NLSP).
CHARACTERISTICS OF AN IPX/SPX NUMBER
A datagram passed in an IPX internet work contains the following information:
1. A 30-byte IPX header (includes network, node, and socket number of
both source and destination addresses)
2. Data section: includes SPX header (or some other type, but often SPX)
Since IPX is connectionless, the minimum packet size is only 30-bytes
(excluding MAC header). Since SPX provides reliable connections (but is not
mandatory) it may not be included. IPX has a maximum packet size of 65,535
bytes (includes data obviously). The MAC header comes before the IPX header
and the data. Now, the IPX network number is 4-bytes, hexadecimal. This is
the basis for packet routing. Each destination in internet work has their own
number. The network number may contain up to eight digits, wile leading
zeroes are often not displayed. Novell Server can automatically detect network
numbers on the internet work. Routers send a RIP request packet to determine
network numbers and frame types to use. The Node number is 6 bytes,
hexadecimal. This number uniquely identifies a device on the internet work and
is akin to the interface connected to that device. This number need only be
unique in the IPX network to which it is a member.
HTTP
HTTP (Hypertext Transfer Protocol) is in widespread use today. HTTP
is used to transfer Web pages from a Web server to a local Web browser. Those
Web pages are created as HTML (Hypertext Markup Language) documents.
HTTP also has a sister protocol called HTTP(S), which allows for secure
transfer of documents. While HTTPS is slower due to the overhead generated
by encryption methods, most would agree that it is essential for e-commerce
and on-line banking transactions.
FTP
FTP (File Transfer Protocol) is somewhat unique in that it is both a
protocol and a program. It is usually associated most closely with the UNIX
environment. As the name would indicate, it is used to transfer files. It is very
powerful and flexible in its use. It can be configured to let users take files but
not transmit them. This could be very advantageous in the case of limiting the
transfer of files that may contain a virus.
There is also a stripped down version of FTP called TFTP (Trivial File
Transfer Protocol) which lacks some of the functionality of FTP in particular
the ability to browse for files. Most FTP access is granted using the
“anonymous” user account. FTP can be very useful when troubleshooting or
servicing an IP-based network. It can be used to download fixes, patches and
standard ASCII read me files. The FTP utility is actually a collection of
separate FTP commands. The list below displays some of the most popular
commands along with their use.
� Help Displays Help screen for commands
� CD Changes the directory on a remote disk
� LCD Changes the directory on a local disk
� DIR Displays a descriptive list of files on remote computers
� BINARY Transfers a binary file format
� ASCII Transfers an ASCII file format
� PUT Transmits files to remote computers
� GET Retrieves files from remote computers
� QUIT/BYE Ends and exits an FTP session
SMTP
SMTP (Simple Mail Transfer Protocol) provides a mechanism to send
email between dissimilar operating systems. It is SMTP’s ability to send email
between different operating systems that makes it so useful on the Internet. An
example of this would be composing an email message from a Windows 98
client, forwarding that to a local Microsoft Exchange Server which could then
send it via the Internet to a server running the UNIX operating system.
NNTP
NNTP (Network News Transfer Protocol) is the predominant protocol
used by computer clients and servers for managing the notes posted on Usenet
newsgroups. NNTP replaced the original Usenet protocol, UNIX-to-UNIX
Copy Protocol (UUCP) some time ago. NNTP servers manage the global
network of collected Usenet newsgroups and include the server at your Internet
access provider. An NNTP client is included as part of a Netscape, Internet
Explorer, Opera, or other Web browser or you may use a separate client
program called a newsreader.
P0P3
The POP3 (Post Office Protocol) version 3 is used to download email
from various servers to an email client. Microsoft’s Outlook Express is an
example of client-side software that uses POP3 technology. Most ISPs (Internet
Service Providers) that provide home service also use the POP3 protocol. This
enables the ISP to download messages to the individual user’s computer rather
than having to store them on the ISP’s servers.
Network Components
Network Interface Card
The NIC is perhaps the most common component in the network. At
least one NIC must be installed in every system attached to the network. The
NIC is an expansion board that allows the workstation or server to attach to a
common cabling system. Most network interface cards provide for more than
just one cable type. The most common connection types are twisted pair
(RJ45), coax (BNC) connectors and fiber optic connections.
Cables and Connectors
Coaxial Cable
Coaxial cable is the kind of copper cable used by cable TV companies
between the community antenna and user homes and businesses. Coaxial cable
is sometimes used by telephone companies from their central office to the
telephone poles near users. It is also widely installed for use in business and
corporation Ethernet and other types of local area network. Coaxial cable is
called “coaxial” because it includes one physical channel that carries the signal
surrounded (after a layer of insulation) by another concentric physical channel,
both running along the same axis. The outer channel serves as a ground. Many
of these cables or pairs of coaxial tubes can be placed in a single outer
sheathing and, with repeaters, can carry information for a great distance.
Coaxial cable was invented in 1929 and first used commercially in 1941.
AT&T established its first cross-continental coaxial transmission system in
1940. Depending on the carrier technology used and other factors, twisted pair
copper wire and optical fiber are alternatives to coaxial cable.
BNC Connector used with Coaxial Cable
A BNC (Bayonet Neil-Concelman, or sometimes British Naval
Connector) connector is used to connect a computer to a coaxial cable in a
10BASE-2 Ethernet network.
10BASE-2 is a 10 MHz base band network on a cable extending up to
185 meters - the 2 is a rounding up to 200 meters - without a repeater cable.
10BASE-2 Ethernets are also known as “Thin net”, “thin Ethernet”, or
“cheaper nets”. The wiring in this type of Ethernet is thin, 50 ohm, base band
coaxial cable. The BNC connector in particular is generally easier to install and
less expensive than other coaxial connectors.
A BNC male connector has a pin that connects to the primary
conducting wire and then is locked in place with an outer ring that turns into
locked position. Different sources offer different meanings for the letters BNC.
However, our most knowledgeable source indicates that the B stands for a
bayonet-type connection (as in the way a bayonet attaches to a rifle) and the
NC for the inventors of the connector, Neil and Concelman.
Twisted Pair
Twisted pair is the ordinary copper wire that connects home and many
business computers to the telephone company. To reduce crosstalk or
electromagnetic induction between pairs of wires, two insulated copper wires
are twisted around each other. Each connection on twisted pair requires both
wires. Since some telephone sets or desktop locations require multiple
connections, twisted pair is sometimes installed in two or more pairs, all within
a single cable. For some business locations, twisted pair is enclosed in a shield
that functions as a ground. This is known as shielded twisted pair (STP).
Ordinary wire to the home is unshielded twisted pair (UTP). Twisted pair is
now frequently installed with two pairs to the home, with the extra pair making
it possible for you to add another line (perhaps for modem use) when you need
it. Twisted pair comes with each pair uniquely color coded when it is packaged
in multiple pairs. Different uses such as analog, digital, and Ethernet require
different pair multiples. Although twisted pair is often associated with home
use, a higher grade of twisted pair is often used for horizontal wiring in LAN
installations because it is less expensive than coaxial cable. The wire you buy
at a local hardware store for extensions from your phone or computer modem
to a wall jack is not twisted pair. It is a side-by-side wire known as silver satin.
The wall jack can have as many five kinds of hole arrangements or pin outs,
depending on the kinds of wire the installation expects will be plugged in (for
example, digital, analog, or LAN) . (That’s why you may sometimes find when
you carry your notebook RJ45 Connectors are used with Twisted pair cables.
In the U. S., telephone jacks are also known as registered jacks,
sometimes described as RJ-XX, and are a series of telephone connection
interfaces (receptacle and plug) that are registered with the U.S. Federal
Communications Commission (FCC). They derive from interfaces that were
part of AT&T’s Universal Service Order Codes (USOC) and were adopted as
part of FCC regulations (specifically Part 68, Subpart F. Section 68.502). The
term jack sometimes means both receptacle and plug and sometimes just the
receptacle.
RJ-45
The RJ-45 is a single-line jack for digital transmission over ordinary
phone wire, either untwisted or twisted. The interface has eight pins or
positions. For connecting a modem, printer, or a data PBX at a data rate up to
19.2 Kbps, you can use untwisted wire. For faster transmissions in which
you’re connecting to an Ethernet 10BASET network, you need to use twisted
pair wire. (Untwisted is usually a flat wire like common household phone
extension wire. Twisted is often round.) There are two varieties of RJ-45:
keyed and unkeyed. Keyed has a small bump on its end and the female
complements it. Both jack and plug must match.
Fiber Optic Cable
Fiber optic (or “optical fiber”) refers to the medium and the technology
associated with the transmission of information as light impulses along a glass
or plastic wire or fiber. Fiber optic wire carries much more information than
conventional copper wire and is far less subject to electromagnetic interference.
Most telephone company long-distance lines are now fiber optic. Transmission
on fiber optic wire requires repeating at distance intervals. The glass fiber
requires more protection within an outer cable than copper. For these reasons
and because the installation of any new wiring is labor-intensive, few
communities yet have fiber optic wires or cables from the phone company’s
branch office to local customers (known as local loop).
A Fiber Optic Cable Different kinds of Fiber Optic Connectors
Hubs and Switches
Hub
In general, a hub is the central part of a wheel where the spokes come
together. The term is familiar to frequent fliers who travel through airport
“hubs” to make connecting flights from one point to another. In data
communications, a hub is a place of convergence where data arrives from one
or more directions and is forwarded out in one or more other directions. A hub
usually includes a switch of some kind. (And a product that is called a “switch”
could usually be considered a hub as well.) The distinction seems to be that the
hub is the place where data comes together and the switch is what determines
how and where data is forwarded from the place where data comes together.
Regarded in its switching aspects, a hub can also include a router.
1. In describing network topologies, a hub topology consists of a backbone
(main circuit) to which a number of outgoing lines can be attached
(“dropped”), each providing one or more connection port for device to
attach to. For Internet users not connected to a local area network, this is
the general topology used by your access provider. Other common
network topologies are the bus network and the ring network. (Either of
these could possibly feed into a hub network, using a bridge.)
2. As a network product, a hub may include a group of modem cards for
dial-in users, a gateway card for connections to a local area network (for
example, an Ethernet or a Token Ring), and a connection to a line.
Switch
In a telecommunications network, a switch is a device that channels
incoming data from any of multiple input ports to the specific output port that
will take the data toward its intended destination. In the traditional circuit-
switched telephone network, one or more switches are used to set up a
dedicated though temporary connection or circuit for an exchange between two
or more parties. On an Ethernet local area network (LAN), a switch determines
from the physical device (Media Access Control or MAC) address in each
incoming message frame which output port to forward it to and out of. In a
wide area packet-switched network such as the Internet, a switch determines
from the IP address in each packet which output port to use for the next part of
its trip to the intended destination. In the Open Systems Interconnection (OSI)
communications model, a switch performs the layer 2 or Data-Link layer
function. That is, it simply looks at each packet or data unit and determines
from a physical address (the “MAC address”) which device a data unit is
intended for and switches it out toward that device. However, in wide area
networks such as the Internet, the destination address requires a look-up in a
routing table by a device known as a router. Some newer switches also perform
routing functions (layer 3 or the Network layer functions in OSI) and are
sometimes called IP switches. On larger networks, the trip from one switch
point to another in the network is called a hop. The time a switch takes to
figure out where to forward a data unit is called its latency. The price paid for
having the flexibility that switches provide in a network is this latency.
Switches are found at the backbone and gateway levels of a network where one
network connects with another and at the sub network level where data is being
forwarded close to its destination or origin. The former are often known as core
switches and the latter as desktop switches. In the simplest networks, a switch
is not required for messages that are sent and received within the network. For
example, a local area network may be organized in a Token Ring or bus
arrangement in which each possible destination inspects each message and
reads any message with its address.
Repeaters
A repeater is a signal amplification device. As an electronic signal
travels down a wire it weakens in strength. In electronic jargon this is known as
attenuation. It’s much like a marathon runner getting tired and weakening as
the race progresses. Repeaters are place at predetermined points along the cable
and act to boost and retransmit the signal. This is like giving a runner a power
bar or drink at crucial points in a race.
Bridges
A bridge is a hardware device that segments a single network into two or
more logical pieces for the purpose of isolating network traffic. The operative
word here is a single network. A bridge does NOT create another new network,
because the segments still appear as one single network. Like a drawbridge that
allows or prohibits traffic from passing from one side of the bridge to the other,
a network bridge performs the same function in a network environment. The
bridge will either pass network traffic or deny network traffic based on the
destination address. If the intended address for a piece of data is located on the
“local” segment, the bridge will block the traffic from passing beyond it onto
other segments. On the other hand, if the destination address is on another
segment, the bridge will allow the traffic to pass through in order to reach its
destination. Let’s look at a simple example of why a bridge is used in a
network environment. Let’s say that, within a single network, there is a small
group of computer users that constantly exchange information and access
network resources. On this same network, there is a larger group of users that
do not use the network as much. If this network were not segmented, the first
group would actually impact the performance of the second group in a negative
way. However, if a bridge were used to segment the two groups, the first group
of more intense network users would be isolated. The bridge would identify the
traffic that belonged to the users on this local segment, and would prohibit it
from passing out onto the rest of the network. Only the traffic intended for a
computer located on the other side of the bridge will be allowed to pass. All
other network traffic would remain on the local segment.
Routers
The router is considered to be an intelligent networking device. It
performs basically two functions. First, it provides the physical connection
between two or more different networks. The second and major function is to
route packets of network information between different networks, hence the
name “router.” The router also has the intelligence built in to dynamically
adapt to changes in the network configuration and to route traffic around
downed links. By implementing a number of routers to connect several smaller
networks together, a larger entity known as an inter network is created. When a
computer located on one network wants to send data to a device located on a
remote network, the data is passed to a router located on the local segment (the
default gateway).
Brouters
The brouter is a hybrid device that, as its name would imply, combines
the functionality of both a bridge and a router into one device. It will function
as a router in most cases. However, if it cannot locate the necessary routing
information, it will perform a simple bridging function, either passing or
denying network traffic based on the MAC destination address.
Gateways
If a router is considered an intelligent networking device, the gateway
would be considered the device with a PhD. The gateway basically provides all
the functionality of a router and acts as a translator as well. The router is a
protocol- independent device, meaning it doesn’t really care what language a
computer speaks. It is just interested in getting the message from one machine
to another. The gateway performs the routing function as well as translating
between different computer languages (protocols). An example of this could be
the connection between a Windows NT/2 000 network and an IBM mainframe
environment. The word default gateway refers to a router on the network that
sends all TCP/IP packets to remote networks. The key point here is any or all
packets are sent which are not destined for the local network! Because of the
translation and other overhead involved, the gateway is the least rapid (slowest)
of the Internet work Connection Devices.
Firewalls
A firewall is a set of related programs, located at a network gateway
server that protects the resources of a private network from users from other
networks. (The term also implies the security policy that is used with the
programs.) An enterprise with an intranet that allows its workers access to the
wider Internet installs a firewall to prevent outsiders from accessing its own
private data resources and for controlling what outside resources its own users
have access to.
INTERNET & WWWINTERNET & WWWINTERNET & WWWINTERNET & WWW
Basic Concepts of Internet
The Internet
The Internet is a computer network made up of thousands of networks
worldwide. No one knows exactly how many computers are connected to the
Internet. It is certain, however, that these number in the millions.
No one is in charge of the Internet. There are organizations which
develop technical aspects of this network and set standards for creating
applications on it, but no governing body is in control. The Internet backbone,
through which Internet traffic flows, is owned by private companies.
All computers on the Internet communicate with one another using the
Transmission Control Protocol/Internet Protocol suite, abbreviated to TCP/IP.
Computers on the Internet use client/server architecture. This means that the
remote server machine provides files and services to the user’s local client
machine. Software can be installed on a client computer to take advantage of
the latest access technology.
An Internet user has access to a wide variety of services: electronic mail,
file transfer, vast information resources, interest group membership, interactive
collaboration, multimedia displays, real-time broadcasting, shopping
opportunities, breaking news, and much more.
The Internet consists primarily of a variety of access protocols. Many of
these protocols feature programs that allow users to search for and retrieve
material made available by the protocol.
Brief history
The Internet (which most people know today as the World Wide Web or
WWW) began in the United States in the 1960’s as a military project. It linked
computers and people together so that if one military base was destroyed,
information could still reach its destination simply by taking an alternative
route. This approach to linking or networking computers is still the basis of the
Internet.
Academic institutions adopted this technology to allow co-operative
work between universities, and the internet grew from there, although when the
Internet first started, people could only share text-based documents.
In 1990, the World Wide Web was developed. This made the internet
very popular, because the WWW allowed people to access information through
a graphical (picture based) interface such as the well-known browser, Netscape.
Components of the Internet
World Wide Web (WWW)
The World Wide Web (abbreviated as the Web or WWW) is a system of
Internet servers that supports hypertext to access several Internet protocols on a
single interface. Almost every protocol type available on the Internet is
accessible on the Web. This includes email, FTP, Telnet, and Usenet News. In
addition to these, the World Wide Web has its own protocol: Hypertext
Transfer Protocol, or HTTP. These protocols will be explained later in this
document.
The World Wide Web provides a single interface for accessing all these
protocols. This creates a convenient and user-friendly environment. It is no
longer necessary to be conversant in these protocols within separate, command-
level environments. The Web gathers together these protocols into a single
system. Because of this feature, and because of the Web’s ability to work with
multimedia and advanced programming languages, the Web is the fastest-
growing component of the Internet.
The operation of the Web relies primarily on hypertext as its means of
information retrieval. Hypertext is a document containing words that connect to
other documents. These words are called links and are selectable by the user. A
single hypertext document can contain links to many documents. In the context
of the Web, words or graphics may serve as links to other documents, images,
video, and sound. Links may or may not follow a logical path, as each
connection is programmed by the creator of the source document. Overall, the
Web contains a complex virtual web of connections among a vast number of
documents, graphics, videos, and sounds.
Producing hypertext for the Web is accomplished by creating documents
with a language called Hypertext Markup Language, or HTML. With HTML,
tags are placed within the text to accomplish document formatting, visual
features such as font size, italics and bold, and the creation of hypertext links.
Graphics and multimedia may also be incorporated into an HTML document.
HTML is an evolving language, with new tags being added as each upgrade of
the language is developed and released. The World Wide Web Consortium
(W3C), led by Web founder Tim Berners -Lee, coordinates the efforts of
standardizing HTML. The W3C now calls the language XHTML and considers
it to be an application of the XML language standard.
The World Wide Web consists of files, called pages or home pages,
containing links to documents and resources throughout the Internet.
Electronic mail, or e-mail, allows computer users locally and worldwide
to exchange messages. Each user of e-mail has a mailbox address to which
messages are sent.
Messages sent through e-mail can arrive within a matter of seconds. A
powerful aspect of e-mail is the option to send electronic files to a person’s e-
mail address. Non-ASCII files, known as binary files, may be attached to e-
mail messages. These files are referred to as MIME attachments. MIME stands
for Multimedia Internet Mail Extension, and was developed to help e-mail
software handle a variety of file types. For example, a document created in
Microsoft Word can be attached to an e-mail message and retrieved by the
recipient with the appropriate e-mail program. Many email programs, including
Eudora, Netscape Messenger, and Microsoft Outlook, offer the ability to read
files written in HTML, which is itself a MIME type.
Telnet
Telnet is a program that allows you to log into computers on the Internet
and use online databases, library catalogs, chat services, and more. There are
no graphics in Telnet sessions, just text. To Telnet to a computer, you must
know its address.
This can consist of words (locis.loc.gov) or numbers (140.147.254.3).
Some services require you to connect to a specific port on the remote computer.
In this case, type the port number after the Internet address. Example: telnet
nri.reston.va.us 185. Telnet is available on the World Wide Web. Probably the
most common Web-based resources available through Telnet have been library
catalogs, though most catalogs have since migrated to the Web. A link to a
Telnet resource may look like any other link, but it will launch a Telnet session
to make the connection. A Telnet program must be installed on your local
computer and configured to your Web browser in order to work. With the
increasing popularity of the Web, Telnet has become less frequently used as a
means of access to information on the Internet.
FTP
FTP stands for File Transfer Protocol. This is both a program and the
method used to transfer files between computers. Anonymous FTP is an option
that allows users to transfer files from thousands of host computers on the
Internet to their personal computer account. FTP sites contain books, articles,
software, games, images, sounds, multimedia, course work, data sets, and
more. If your computer is directly connected to the Internet via an Ethernet
cable, you can use one of several PC software programs, such as WS_FTP for
Windows, to conduct a file transfer.
Mail Discussion Groups
One of the benefits of the Internet is the opportunity it offers to people
worldwide to communicate via e-mail. The Internet is home to a large
community of individuals who carry out active discussions organized around
topic-oriented forums distributed by email. These are administered by software
programs. Probably the most common program is the listserv. A great variety
of topics are covered by listserv, many of them academic in nature. When you
subscribe to a listserv, messages from other subscribers are automatically sent
to your electronic mailbox. You subscribe to a listserv by sending an e-mail
message to a computer program called a list server. List servers are located on
computer networks throughout the world. This program handles subscription
information and distributes messages to and from subscribers. You must have
an e-mail account to participate in a listserv discussion group. Visit Tile.net at
http://tile.net/ to see an example of a site that offers a searchable collection of
e-mail discussion groups.
UseNet News
Usenet News is a global electronic bulletin board system in which
millions of computer users exchange information on a vast range of topics. The
major difference between Usenet News and e-mail discussion groups is the fact
that Usenet messages are stored on central computers, and users must connect
to these computers to read or download the messages posted to these groups.
This is distinct from e-mail distribution, in which messages arrive in the
electronic mailboxes of each list member.
Usenet itself is a set of machines that exchanges messages, or articles,
from Usenet discussion forums, called newsgroups. Usenet administrators
control their own sites, and decide which (if any) newsgroups to sponsor and
which remote newsgroups to allow into the system. There are thousands of
Usenet newsgroups in existence. While many are academic in nature, numerous
newsgroups are organized around recreational topics. Much serious computer-
related work takes place in Usenet discussions. A small number of e-mail
discussion groups also exist as Usenet newsgroups. The Usenet news feed can
be read by a variety of newsreader software programs. For example, the
Netscape suite comes with a newsreader program called Messenger.
Newsreaders are also available as standalone products.
Chat and Instant Massaging
Chat programs allow users on the Internet to communicate with each
other by typing in real time. They are sometimes included as a feature of a Web
site, where users can log into the “chat room” to exchange comments and
information about the topics addressed on the site. Chat may take other, more
wide-ranging forms. For example, America Online is well known for
sponsoring a number of topical chat rooms. Internet Relay Chat (IRC) is a
service through which participants can communicate to each other on hundreds
of channels. These channels are usually based on specific topics. While many
topics are frivolous, substantive conversations are also taking place. To access
IRC, you must use an IRC software program.
A variation of chat is the phenomenon of instant messaging. With
instant messaging, a user on the Web can contact another user currently logged
in and type a conversation. Most famous is America Online’s Instant
Messenger. ICQ, MSN and Yahoo are other commonly-used chat programs.
Evolution of Internet
The history of the Internet begins at the height of the cold war in the
1960’s. People at the Rand Corporation, America’s foremost military think
tank, were trying to figure out an important strategic problem: how could US
authorities talk to each other in the aftermath of a nuclear attack?
Communication networks of the day were chained point-to-point, with each
place on the network dependent on the link before it. If one point in the
network was blown up, the whole network would become useless. Paul Baran,
one of the Rand thinkers on the project, conceived the idea for a new kind of
communications network; one that wasn’t organized point-to-point, but instead
was set up more like a fishnet. He believed this structure could allow
information to find its own path through the network even if a section had been
destroyed. His eleven volume report for the Pentagon was eventually shelved;
but younger engineers realized that he had hit on an essential idea. Baran’s
Cold War musings later influenced the design used to create a small,
decentralized network connecting computers at four university campuses
around the United States. This tiny seed eventually grew into the Internet; a
huge network-of networks, millions of nodes strong, which today covers the
entire globe. The Internet has come a long way from its military beginnings.
Touching almost every aspect of society, it is now more likely to be used to
plan a family vacation than to transmit military secrets. Following are
highlights of the 30 year history of the Internet; how it grew, what technologies
grew with it, and the impact of success on the Internet itself.
1962 - 1969
The Internet is first conceived in the early ’60s. Under the leadership of
the Department of Defense’s Advanced Research Project Agency (ARPA), it
grows from a paper architecture into a small network (ARPANET) intended to
promote the sharing of supercomputers amongst researchers in the United
States.
� 1962 – The RAND Corporation begins research into robust, distributed
communication networks for military command and control.
� 1965 - ARPA sponsors research into a “cooperative network of time-
sharing computers.”
� 1967 - Delegates at a symposium for the Association for Computing
Machinery in Gatlinburg, TN discuss the first plans for the ARPANET.
� 1969 - Researchers at four US campuses create the first hosts of the
ARPANET, connecting Stanford Research Institute, UCLA, UC Santa
Barbara, and the University of Utah.
1970 - 1973
The ARPANET is a success from the very beginning. Although
originally designed to allow scientists to share data and access remote
computers, email quickly becomes the most popular application. The
ARPANET becomes a high-speed digital post office as people use it to
collaborate on research projects and discuss topics of various interests.
� 1971 - The ARPANET grows to 23 hosts connecting universities and
government research centers around the country.
� 1972 - The Inter Networking Working Group becomes the first of
several standards-setting entities to govern the growing network. Vinton
Cerf is elected the first chairman of the INWG, and later becomes
known as a “Father of the Internet.”
� 1973 - The ARPANET goes international with connections to
University College in London, England and the Royal Radar
Establishment in Norway.
1974 - 1981
The general public gets its first vague hint of how networked computers
can be used in daily life as the commercial version of the ARPANET goes
online. The ARPANET starts to move away from its military/research roots. ·
1974 - Bolt, Beranek & Newman opens Telnet, the first commercial version of
the ARPANET.
� 1976 - Queen Elizabeth goes online with the first royal email message.
� 1979 - Tom Truscott and Jim Ellis, two graduate students at Duke
University, and Steve Bellovin at the University of North Carolina
establish the first USENET newsgroups. Users from all over the world
join these discussion groups to talk about the net, politics, religion and
thousands of other subjects.
� 1981 - ARPANET has 213 hosts. A new host is added approximately
once every 20days.
1982 - 1987
Bob Kahn and Vinton Cerf are key members of a team which creates
TCP/IP (Transmission Control Protocol/Internet Protocol: TCP makes sure data
arrives correctly and in the proper order. IP specifies the way in which data will
be communicated between two computers on a network), the common
language of all Internet computers. For the first time the loose collection of
networks which made up the ARPANET is seen as an “Internet”, and the
Internet as we know it today is born. The mid-80s marks a boom in the
personal computer and super-minicomputer industries. The combination of
inexpensive desktop machines and powerful, network-ready servers allows
many companies to join the Internet for the first time. Corporations begin to
use the Internet to communicate with each other and with their customers.
� 1982 - The term “Internet” is used for the first time.
� 1984 - William Gibson coins the term “cyberspace” in his novel
“Necromancer.” The number of Internet hosts exceeds 1,000.
� 1986 - Case Western Reserve University in Cleveland, Ohio creates the
first “Free net” for the Society for Public Access Computing.
� 1987-The number of Internet hosts exceeds 10,000.
1988 – 1990
By 1988 the Internet is an essential tool for communications; however it
also begins to create concerns about privacy and security in the digital world.
New words, such as “hacker,” “cracker” and” electronic break-in”, are created.
These new worries are dramatically demonstrated on Nov. 1, 1988 when a
malicious program called the “Internet Worm” temporarily disables
approximately 6,000 of the 60,000 Internet hosts.
� 1988 - The Computer Emergency Response Team (CERT) is formed to
address security concerns raised by the Worm.
� 1989 - System administrator turned author, Clifford Stoll, catches a
group of Cyber spies, and writes the best-seller “The Cuckoo’s Egg.”
The number of Internet hosts exceeds 100,000.
� 1990 - A happy victim of its own unplanned, unexpected success, the
ARPANET is decommissioned, leaving only the vast network-of-
networks called the Internet. The number of hosts exceeds 300,000.
1991 - 1993
Corporations wishing to use the Internet face a serious problem:
commercial network traffic is banned from the National Science Foundation’s
NSFNET, the backbone of the Internet. In 1991 the NSF lifts the restriction on
commercial use, clearing the way for the age of electronic commerce. At the
University of Minnesota, a team led by computer programmer Mark
MaCahillreleases “gopher,” the first point-and-click way of navigating the files
of the Internet in 1991. Originally designed to ease campus communications,
gopher is freely distributed on the Internet. MaCahill calls it “the first Internet
application my mom can use.” 1991 is also the year in which Tim Berners-Lee,
working at CERN in Switzerland, posts the first computer code of the World
Wide Web in a relatively innocuous newsgroup, “alt.hypertext.” The ability to
combine words, pictures, and sounds on Web pages excites many computer
programmers who see the potential for publishing information on the Internet
in a way that can be as easy as using a word processor. Marc Andreessen and a
group of student programmers at NCSA (the National Center for
Supercomputing Applications located on the campus of University of Illinois at
Urbana Champaign) will eventually develop a graphical browser for the World
Wide Web called Mosaic.
� 1991 - Traffic on the NSF backbone network exceeds 1 trillion bytes per
month.
� 1992 - The first audio and video broadcasts take place over a portion of
the Internet known as the “MBONE.” More than 1,000,000 hosts are
part of the Internet.
� 1993 - Mosaic, the first graphics-based Web browser, becomes
available. Traffic on the Internet expands at a 341,634% annual growth
rate.
1994 - 1996
As the Internet celebrates its 25th anniversary, the military strategies that
influenced its birth become historical footnotes. Approximately40 million
people are connected to the Internet. More than $1 billion per year changes
hands at Internet shopping malls, and Internet related companies like Netscape
are the darlings of high-tech investors. The Age of the Internet has arrived. ·
1994 - The Rolling Stones broadcast the Voodoo Lounge tour over the M-
Bone. Marc Andresen and Jim Clark form Netscape Communications Corp.
Pizza Hut accepts orders for a mushroom, pepperoni with extra cheese over the
net, and Japan’s Prime Minister goes online at www.kantei.go.jp. Backbone
traffic exceeds 10 trillion bytes per month. · 1995 - NSFNET reverts back to a
research project, leaving the Internet in commercial hands. The Web now
comprises the bulk of Internet traffic. The Vatican launches www.vatican.va.
James Gosling and a team of programmers at Sun Microsystems release an
Internet programming language called Java, which radically alters the way
applications and information can be retrieved, displayed, and used over the
Internet.
� 1996 - Users in almost 150 countries around the world are now
connected to the Internet. The number of computer hosts approaches 10
million.
Within 40 years, the Internet has grown from a Cold War concept for
controlling the tattered remains of a post-nuclear society to the Information
Superhighway. Just as the railroads of the 19th century enabled the Machine
Age, and revolutionized the society of the time, the Internet takes us into the
Information Age, and profoundly affects the world in which we live. Today
some people telecommute over the Internet, allowing them to choose where to
live based on quality of life, not proximity to work. Many cities view the
Internet as a solution to their clogged highways and fouled air. Schools use the
Internet as a vast electronic library, with untold possibilities. Doctors use the
Internet to consult with colleagues half a world away. And even as the Internet
offers a single Global Village, it threatens to create a 2nd class citizenship
mongo those without access. As a new generation grows up as accustomed to
communicating through a keyboard as in person, life on the Internet will
become an increasingly important part of life on Earth. The evolution of the
Internet can at best be described as a phenomenon. It had gone from near
invisibility to near ubiquity in only a short period. The sad conclusions that
many people may draw lead them to believe that since the Internet became
popular overnight, it was created overnight. The ignorance of the common
citizen unfortunately does no justice to the hard work and efforts of the many
scientists, students, and intellectuals who collaborated and created this
technological masterpiece covering the world called the Internet.
Internet Working
How the Internet Works
The Internet is the world’s largest distributed system; it was designed
and engineered for redundancy (it has an abundance of routes and connections)
and resilience (it easily recovers from a mishap). The Internet is not a single
company or a group of companies, nor even a single network. It is a worldwide
mesh or matrix of hundreds of thousands of networks, owned and operated by
hundreds of thousands of people in hundreds of countries, all interconnected by
about 8,000 ISPs (Internet Service Providers). No single organization controls
the Internet; not the U.N.; not the biggest ISPs; and the Internet has long since
outgrown control by the U.S. government.
The Internet is different from other major services. Electricity tends to
be provided by a single company in each geographical area. The “last mile” of
telephone service to the customer is usually owned by a single company. But in
general there is more than one Internet provider in any locale, and there are
usually many paths from a local provider in one area to a provider in another
area.
When you, the user, look at a web page through the Internet, many
things happen along the way. There are various ways to get from your house or
office through the “last mile” to the Internet: modem dialup, ISDN, DSL, cable
modem, wireless, leased line, etc. These various technical methods may
provide speeds anywhere from very slow (a few hundred bits per second) to
very fast (billions of bits per second). All these access methods are onramps to
the information superhighway.
In order to transmit text or pictures, your data is chopped up into small
packets which are routed through the Internet. But first they have to go from
you to your local ISP, or the equivalent piece of the Internet inside your
organization (an intranet). This local ISP is a possible point of failure. If
something goes wrong at your local ISP, it may look to you like the Internet is
broken. It’s not. Only one small piece of it is broken. The rest of the Internet,
with its portals and stock portfolios and shops and reams of scientific data and
plethora of information and people on it will not break because one ISP does.
To reach a web server, your local ISP sends your packets of data to another
ISP, which may send them to another ISP, or through an Exchange Point (IX)
or a National Access Point (NAP) or Local Access Point (LAP) to get to
another ISP. Thus your packets pass through a chain of ISPs through nodal
points to reach their destination. Your packets may pass through fiber optic
cables in the ground, satellites in the sky, undersea cables, or radio links. They
may travel at speeds including T-1 (1.544 Mbps), T-3 (45Mbps), or faster (or
slower). The Internet Protocol (IP) ties all of those links together, enabling your
packets travel through the Internet.
Eventually your packets arrive at the web server, and the web server
sends responses back along a similar path (almost definitely not the same one).
Any of these Internet providers can have problems (congestion, broken link,
power outage, broken computer, etc.), which may cause the web server to seem
slow or unresponsive to you. But the web server is broken only if the web
server is actually broken. Problems in intervening parts of the Internet do not
break the web server, which may well be accessible to other people, and may
become accessible to you as soon as the various Internet providers route your
traffic around problems. Much rerouting in the Internet is dynamic, and
happens automatically. (Imagine you are driving up the California coast and
come to a sign that says that there has been a mudslide. You drive inland, north
on another road, perhaps rejoining the coastal highway again. You have
changed your route dynamically.) Some rerouting isn’t automatic. In particular,
the biggest ISPs, frequently called backbones, cover vast geographical areas
and carry large proportions of the Internet’s traffic. A failure in a backbone or
in one of the major interconnection points between them can affect many
Internet users. And such a problem may take some time to be resolved, as the
biggest ISPs often prefer to manually examine changes in major routes before
implementing them. But longstanding observation of the Internet indicates that
“some time” is normally at most few hours, even in the face of the biggest
problems.
Internet providers use the same methods for routing packets for
electronic mail or file transfers or remote login or voice or video. People tend
to be quicker to notice slowness in accessing web pages, so we have used
accessing a web server as an example. There are other key pieces of the
Internet, most notably the root name servers. Name servers translate domain
names, such as www.ripe.net, into the IP addresses, such as 193.0.0.195, that
are used by the Internet protocols in carrying your packets through the Internet.
The root name servers handle the most basic part of that translation, which is
finding name servers for the top level domains (TLDs), such as NET, COM,
ORG, EDU, GOV, FR (France), JP (Japan), AU (Australia), or PE (Peru). The
root name servers are widely spaced in both geography and in Internet
topology, so that a failure in one cannot readily affect another. The root name
server operators have also cooperated in extensively testing their software,
hardware, and capacities, and they all know how to reach each other in case
they perceive problems. The rest of the Domain Name Service (DNS) is
distributed among hundreds of thousands of name servers for the various
domains. For example, there are name servers for ORG, and then there are
name servers for MIDS.ORG. Every domain is supposed to have at least two
independent name servers, and most do (another instance of redundancy). In
any case, a failure in a single name server may make a particular domain
temporarily inaccessible, but it will not affect the Internet at large.
The decentralization of the Internet is one of its biggest advantages and
one of its most basic features, designed into its protocols from the beginning
and tested in practice over many years. If one piece breaks, that doesn’t mean
the Internet is broken. And decentralization requires cooperation, so the various
ISPs and IXes and the like are accustomed to cooperating with one another to
fix and prevent problems. It is this decentralization and cooperation that has
permitted the Internet to grow faster for longer than any other technological
phenomenon in history. It is important for you, the user, to understand how
decentralization makes the Internet work, so that you will know that the
Internet is actually very hard to break.
Internet Services
Some of the most popular Internet services include electronic mail (e-
mail), the World Wide Web (WWW), Chat, Internet News, File Transfer
Protocol (FTP), and Telnet.
Electronic mail (e-mail)
E-mail is the most popular service on the Internet. You can use it to send
messages to any user connected to the Internet.
World Wide Web (WWW)
The World Wide Web, or the Web, is a term used to describe the
interlinked collection of hypertext documents and multimedia content available
on the Internet. Hypertext documents are files that have been formatted for use
on the Internet. You use a Web browser, such as Microsoft Internet Explorer, to
search for, locate, view, and download information from the Internet.
Chat
Chat programs allow you to participate in a real-time conversation with
two or more people on the Internet.
Internet News
Internet News is a service that hosts electronic discussion groups
through which participants can share information and opinions. A news client,
such as Microsoft Outlook® Express, can then be used to access these groups.
File Transfer Protocol (FTP)
FTP is a service that includes a server for transferring files from the
server to a client computer. Users can download files from the FTP server by
using an FTP client utility.
Telnet
Telnet offers a way to remotely log on to a computer and work on that
computer. By logging on to this computer remotely, users can access services
or resources that they may not have on their own workstation.
Internet Access Methods
Connections to the Internet can be described in four basic categories:
dialup, proxy, direct and leased.
A dialup connection
A dialup connection is attained through a modem or similar device. The
connection typically provides between 2400 bps (bits per second) and 28,800
bps throughputs, which is usually more than adequate for e-mail and for
running processes on the remote host. While this type of connection is usually
adequate for line-oriented access, it is not suitable for full-screen programs. For
instance, utilities such as Mosaic expect to be able to address the full screen of
a machine that is directly connected to the internet. To make full use of many
of the current Internet resources, then, a more advanced connection is
required—at minimum, a proxy connection.
A proxy connection
A proxy connection is also typically made through a modem, but it has
special provisions that enable full Internet access. SLIP (Serial Line IP) and
PPP (Point-to-Point Protocol) are two examples of such provisions (both
discussed later in this chapter). Tools such as FTP, Gopher and Mosaic are
thereby available for use just as if the connection were directly on the Internet.
Direct connections
Direct connections are obtained when the machine being used has a
dedicated circuit to the Internet. This can still be a remote connection, but it has
the full functionality of a directly connected machine. A good example is ISDN
(Integrated Services Digital Network), which is discussed later in this chapter.
Leased line
Lastly, the leased line is a circuit leased from the local telephone
company that provides a permanent address on the Internet. The advantage of a
permanent address is that it that enables services such as FTP or Gopher to be
set up. The leased line varies in throughput from 9600 bps to 45,000,000 bps
(45 Mbps).
Internet Service Provider
ISP definition
An Internet Service Provider, or ISP, is a company that provides its
customers with access to the Internet. Customers may connect to their ISP
through dialup (telephone), broadband (including DSL, ISDN and cable
modem services), or wireless connections. There are countless national and
regional ISPs, and a great many websites exist to help you locate the best one
for you. There are many different ISP’s which provide a broad variety of
services at a broad variety of prices. An ISP has the equipment and the
telecommunication line access required to have a point-of-presence on the
Internet for the geographic area served.
The larger ISPs have their own high-speed leased lines so that they are
less dependent on the telecommunication providers and can provide better
service to their customers. Among the largest national and regional ISPs are
AT&T WorldNet, IBM Global Network, MCI, Netcom, UUNet, and PSINet.
ISPs also include regional providers such as New England’s NEAR Net and the
San Francisco Bay area BAR Net. They also include thousands of local
providers. In addition, Internet users can also get access through online service
providers (OSP) such as America Online and CompuServe. The larger ISPs
interconnect with each other through MAE (ISP switching centers run by MCI
WorldCom) or similar centers. The arrangements they make to exchange traffic
are known as peering agreements. There are several very comprehensive lists
of ISPs world-wide available on the Web. An ISP is also sometimes referred to
as an IAP (Internet access provider).
ISP is sometimes used as an abbreviation for independent service
provider to distinguish a service provider that is an independent, separate
company from a telephone company.
The Types and Functions of Modems
The Origin of Modems
The word “modem” is a contraction of the words modulator-
demodulator. A modem is typically used to send digital data over a phone line.
The sending modem modulates the data into a signal that is compatible with the
phone line, and the receiving modem demodulates the signal back into digital
data. Wireless modems convert digital data into radio signals and back.
Modems came into existence in the 1960s as a way to allow terminals to
connect to computers over the phone lines. A typical arrangement is shown
below:
In a configuration like this, a dumb terminal at an off-site office or store
could “dial in” to a large, central computer. The 1960s were the age of time -
shared computers, so a business would often buy computer time from a time-
share facility and connect to it via a 300-bit-per-second (bps) modem. A dumb
terminal is simply a keyboard and a screen. A very common dumb terminal at
the time was called the DEC VT-100, and it became a standard of the day (now
memorialized in terminal emulators worldwide). The VT-100 could display 25
lines of 80 characters each. When the user typed a character on the terminal,
the modem sent the ASCII code for the character to the computer. The
computer then sent the character back to the computer so it would appear on
the screen. When personal computers started appearing in the late 1970s,
bulletin board systems (BBS) became the rage. A person would set up a
computer with a modem or two and some BBS software, and other people
would dial in to connect to the bulletin board. The users would run terminal
emulators on their computers to emulate a dumb terminal.
IP Addressing
What Is an IP Address?
Each TCP/IP host is identified by a logical IP address. A unique IP
address is required for each host and network component that communicates by
using TCP/IP. The IP address identifies a system’s location on the network in
the same way that a street address identifies a house on a city block. Just as a
street address must identify a unique residence, an IP address must be globally
unique and have a uniform format.
Network ID
Each IP address defines the network ID and host ID. The network ID
identifies the systems that are located on the same physical segment. All
systems on the same physical segment must have the same network ID. The
network ID must be unique to the internet work.
Host ID
The host ID identifies a workstation, server, router, or other TCP/IP host
within a segment. The address for each host must be unique to the network ID.
Network ID and Host ID
Each IP address is 32 bits long and is composed of four 8-bit fields,
called octets. Octets are separated by periods. The octet represents a decimal
number in the range 0–255. This format is called dotted decimal notation. The
following is an example of an IP address in binary and dotted decimal formats.
Internet Domains
In the old days, where the Internet barely had 200 hosts, every host
knew the address of every other host on the Internet. Every host also associated
a human-readable name with every other host’s IP address so that the user
didn’t have to remember all those numbers. Now the Internet has millions of
hosts connected to it, however, so keeping track of every host on every
computer isn’t just impractical, it’s impossible. You certainly can access a host
by its IP address. For example, to access my host, you’d use 206.50.127.46. To
access Macmillan’s host, you’d use 206.246.150.10. Why use an IP address,
however, when you can use a domain name instead? A domain name is a
unique, human- readable name for a host on the Internet. Domain names are
case sensitive, by the way. For example, honeycutt.com, mcp.com, and
microsoft.com are examples of domain names.
Domain names are divided into parts with a period, just like an IP
addresses. Whereas an IP address gets more specific as you look from left to
right, domain names get more specific as you look from right to left. In general,
domain names follow this format: hostname. Second-level. first-level
First-level. The first-level domain is the least specific. You’ll see first-
level domains like com and uk, which represent the type of organization or
country in which the host belongs. Table 2.1 describes some of the first-level
domains that are typical on the Internet. First-level domains are also called
zones or top-level domains. Second-level The second-level domain identifies
the organization that owns or operates the network to which the host is
attached. Every organization that has a network attached to the Internet has
registered their second-level domain. The name usually represents the
company’s name or trade. For example: microsoft.com, honeycutt.net, and
whitehouse.gov. Host-name The host-name identifies the host on the network
represented by the first- and second-level domains. The host-name isn’t
registered because the network on which the host resides worries about routing
traffic to the host based upon its name. That is, the only information that the
Internet’s routers need to route traffic to the host is the first- and second-level
domains. The host’s network worries about routing traffic to the host given its
host-name.
First-Level Domain Names
Name Description
.com Commercial and for-profit organizations
.edu Universities & Education Organization
.gov Federal government agencies
.mil U.S. military sites
.net Internet infrastructure and service providers
.org Miscellaneous and non-profit organizations
TCP/IP Protocol
TCP/IP (Transmission Control Protocol/Internet Protocol) is the basic
communication language or protocol of the Internet. It can also be used as a
communications protocol in a private network (either an intranet or an
extranet). When you are set up with direct access to the Internet, your computer
is provided with a copy of the TCP/IP program just as every other computer
that you may send messages to or get information from also has a copy of
TCP/IP. TCP/IP is a two-layer program. The higher layer, Transmission
Control Protocol, manages the assembling of a message or file into smaller
packets that are transmitted over the Internet and received by a TCP layer that
reassembles the packets into the original message. The lower layer, Internet
Protocol, handles the address part of each packet so that it gets to the right
destination. Each gateway computer on the network checks this address to see
where to forward the message. Even though some packets from the same
message are routed differently than others, they’ll be reassembled at the
destination. TCP/IP uses the client/server model of communication in which a
computer user (a client) requests and is provided a service (such as sending a
Web page) by another computer (a server) in the network. TCP/IP
communication is primarily point-to-point, meaning each communication is
from one point (or host computer) in the network to another point or host
computer. TCP/IP and the higher-level applications that use it are collectively
said to be “stateless” because each client request is considered a new request
unrelated to any previous one (unlike ordinary phone conversations that require
a dedicated connection for the call duration). Being stateless frees network
paths so that everyone can use them continuously. (Note that the TCP layer
itself is not stateless as far as any one message is concerned. Its connection
remains in place until all packets in a message have been received.)
Many Internet users are familiar with the even higher layer application
protocols that use TCP/IP to get to the Internet. These include the World Wide
Web’s Hypertext Transfer Protocol (HTTP), the File Transfer Protocol (FTP),
Telnet (Telnet) which lets you logon to remote computers, and the Simple Mail
Transfer Protocol (SMTP). These and other protocols are often packaged
together with TCP/IP as a “suite.” Personal computer users usually get to the
Internet through the Serial Line Internet Protocol (SLIP) or the Point-to-Point
Protocol (PPP). These protocols encapsulate the IP packets so that they can be
sent over a dial-up phone connection to an access provider’s modem. Protocols
related to TCP/IP include the User Datagram Protocol (UDP), which is used
instead of TCP for special purposes. Other protocols are used by network host
computers for exchanging router information. These include the Internet
Control Message Protocol (ICMP), the Interior Gateway Protocol (IGP), the
Exterior Gateway Protocol (EGP), and the Border Gateway Protocol (BGP).
The Intranet
An intranet shares most of the characteristics of the Internet, but in at
least one way, it’s fundamentally different. And just as the Internet has had
profound effect on how we communicate, intranets have transformed the
business world as well. Both Fortune 500 companies and small businesses have
implemented this infrastructure, improving productivity while reducing costs.
Just what is an intranet? Think of it as a mini-Internet designed to be used
within the confines of a company, university or organization. What
distinguishes an intranet from the freely accessible Internet is that intranets are
private.
Evolution of WWW
Ever since the Internet merged as an emblem in our mind, the World
Wide Web (WWW) has been exploding into all the aspects of our work, studies
and leisure life. Within the employment market, jobs requiring knowledge of
the Web, Internet and e-Commerce have been most in demand from both
employer and employee’s perspectives. As an employer or employee coping
with the ever changing IT work environment, you should have a fair
understanding of the history, development, capabilities and the future of
WWW. In a series of informative articles, I will introduce all issues associated
with the World Wide Web from the employment perspective. Here I begin with
the 30-year evolution of WWW to preface the series.
Client/Server computing
Increasing numbers of users have to share data. Programs are divided
into two parts: client and server.
1. Client applications that run on local machines allow users to manipulate
centralized data.
2. Server applications that run on centralized machines coordinate sharing
of the data amongst many users.
Middleware software provides transparency between servers and clients
in three-tier client/server systems.
The Internet
The attempts to connect all private and public networks are successful
with the appearance of the Internet. Internet Protocol (IP) becomes a de-facto
standard network protocol of exchanging data between various networks.
Transport Control Protocol (TCP) becomes a de-facto standard transport
protocol on top of IP. Their combination is referred to as the TCP/IP standard.
The World Wide Web
WWW originated as a framework for electronic publishing of hypertext.
1. HTML – Hypertext Markup Language.
2. HTTP – Hypertext Transfer Protocol.
The scope of content published on the Web pages expands daily and
includes text, graphics, sound and video. A Web browser is becoming a new
operating system for many users. Other traditional network applications like
email, file transfer, telnet/remote login have been incorporated under the same
browser roof with the Universal Resource Locator (URL). New business
opportunities have emerged in electronic publishing and commerce. New
technologies like search engines, agents, etc., mix with not-so-new ones like
data mining to address arising challenges. Any user can access any computer
anywhere in the world using the Internet.
Connecting to Internet
How to Connect to the Internet
Before you can connect to the Internet and access the World Wide Web,
you need to have certain equipment. In brief, you must have a computer
(preferably running an up to- date operating system); a modem and access to a
telephone line or a local area network (LAN) that is in turn connected to the
Internet; and connection software that will allow you to establish an account
with a service provider and access the Internet. A modem is not needed when
accessing the Internet through a LAN
The Right Hardware
To operate most of the current Web browsers and on-line services, you
should have an IBM PC/PC equivalent, UNIX workstation, or Apple
Macintosh computer with at least 8 megabytes (MB) of random access
memory (RAM) and 10 MB of free disk space. If you are unsure of how much
RAM and disk space your computer has, consult your user’s manual. For best
results, use a PC with a 486 or Pentium microprocessor; or a Macintosh with a
030, 040 or PowerPC microprocessor. It is possible to connect to the Internet
using a computer other than an IBM PC, Macintosh or UNIX workstation,
though the access software available for such machines is limited. If you are
accessing the Internet outside of a LAN environment, you will need a modem
that will connect you with other computers and interpret the data being sent
back and forth. Most any modem that is compatible with your computer will
do, though the higher the kilobits per second (kbps) rate of your modem, the
faster it will transmit data. Modem speed is an important consideration when
accessing sites on the Web that contain lots of digitized data. In general, your
modem should transmit data at 14.4 kbps or faster to give you optimum
performance on the Web. If you are looking to purchase a modem, buy the
fastest model you can afford. You must also have access to a live telephone
line. Most modems accept the same jacks as do ordinary household telephones,
allowing you to connect your modem to a wall jack using standard phone cord.
Some cable TV providers have begun offering Internet connections via cable.
Such connections provide much faster transmission speeds than standard phone
lines, though you will need a special modem that allows you to link your
computer with the cable. If you are interested in a cable Internet connection,
contact your local cable operator to see if the service is available in your area.
You can also connect to the Internet through a LAN with Internet access. If
you are unsure as to the capacities of your LAN to do this, contact your site’s
systems administrator
The Right Software
For best results, make sure that your computer is running the most up-
to-date operating system that it can handle. If you have an IBM PC/PC
compatible computer, it should be running Microsoft Windows version 3.1,
Windows NT, Windows 95 or OS/2. If you have a Macintosh, it should be
running System 7 or higher. To make your connection complete, you will need
connection software that allows your computer to dial into an Internet access
provider, establish an account, and work with the data in a straightforward
manner. Many access providers will give you software that will allow you to
access their systems using an all-in-one custom interface. Others may give you
a collection of separate software packages that can be used together. But
whatever software they provide, be sure that it is compatible with your
computer and operating system before attempting to use it.
Some Internet access providers may allow you to establish a serial line
interface protocol (SLIP) or point-to-point protocol (PPP) connection, either of
which essentially makes your computer a part of the Internet. Unlike many
standard dial-up software packages, a SLIP/PPP connection allows you to run
independent software packages such as Web browsers, either one at a time or
simultaneously.
The Browser
As you surf the Web, you will come across sites that state, “This site is
best viewed with…” and then name a particular browser. Many will even
provide a link to a site where you can download the specified browser. Sites
make these recommendations because some browsers use special protocols,
allowing site creators to offer extra features beyond the standard capabilities of
hypertext markup language (HTML). Chief among these browsers are Netscape
Navigator and Microsoft Internet Explorer. Your Internet service provider will
most likely give you a choice of browsers so try out a couple, and use the
browser that best suits your needs.
Connection Options
Until recently, the two primary methods of accessing the Internet were
through a network connection, allowing users of local area networks (LANs)
to go online through their school or workplace systems, and dial-up
connections through a modem and phone line. However, new connection
options allow for greater speeds and flexibility, while keeping costs to a
minimum. The following are some of the newer connection options that you
might want to investigate: · Cable Internet—these systems allow your
computer to connect to the Internet through the same cable that carries your TV
signal. Monthly service charges are usually not much more than standard
modem connection costs, but you have to rent or purchase a “cable modem.”
Additionally, your computer will need an Ethernet card (a special circuit board
that allows for network connections). Not all cable service operators offer this
service; call your local operator for more information.
Web Browsers
The World Wide Web (WWW), or Web, is the portion of the Internet
that provides links to graphical content. The Web has developed into a network
of interactive documents that you can easily locate and read using various Web
browsers, such as Internet Explorer. A Web browser is a client application that
enables the client com putter to gain access to a Web server or other server,
such as an FTP server, running on the Internet. Web browsers can display text
files and various graphic and multimedia format files. A browser also interprets
and displays documents.
Web Servers
Web server is a program that, using the client/server model and the
World Wide Web’s Hypertext Transfer Protocol (HTTP), serves the files that
form Web pages to Web users (whose computers contain HTTP clients that
forward their requests).
Every computer on the Internet that contains a Web site must have a
Web server program. Two leading Web servers are Apache, the most widely-
installed Web server, and Microsoft’s Internet Information Server (IIS). Other
Web servers include Novell’s Web Server for users of its NetWare operating
system and IBM’s family of Lotus Domino servers, primarily for IBM’s
OS/390 and AS/400 customers.
A client computer connects to the Internet or an intranet by using a Web
browser to find information stored and organized on a Web server. A Web
server is a computer that uses TCP/IP to send Web page content to client
computers over a network. A Web server communicates with clients by using
an appropriate protocol, such as HTTP or HTTPS. The terms Web server and
HTTP server are synonymous, because URLs identifying data on a Web server
begin with http. For example, the Microsoft Web site is
http://example.microsoft.com/. Every Web server has an IP address and
perhaps a domain name. For example, when you enter the URL
http://example.microsoft.com/webpage.htm in your Web browser, it sends a
request to the Web server with the domain name microsoft.com. Then the Web
server locates and retrieves the page ms.htm, and sends it to your browser. Web
servers often come as part of a larger package of Internet- and intranet-related
programs for serving e-mail, downloading requests for File Transfer Protocol
(FTP) files, and building and publishing Web pages. Considerations in
choosing a Web server include how well it works with the operating system
and other servers, its ability to handle server-side programming, security
characteristics, and publishing, search engine, and site building tools that may
come with it.
Proxy Servers
Most home and small office networks use a dial-up or modem network
connection to an ISP, which in turn connects them to the Internet. The ISP
assigns a single IP address to each network for connecting to the Internet. In
addition, each computer in a network requires an IP address for Internet
connection. Rather than using separate IP addresses for each computer, it is
more cost-effective to use a single IP address for multiple computers. A proxy
server is a firewall component that enables you to connect multiple computers
in a network to the Internet by using a single IP address. Proxy servers have
two main functions: to improve network performance and filter client requests.
Domain Name Server
The Domain Name System (DNS) is a global network of servers that
translate host names like www.internic.net into dotted numerical IP (Internet
Protocol) addresses, like 198.41.0.6 A DNS server is just a computer that’s
running DNS software. DNS software has two parts:
1. The actual name server
2. A resolver.
The name server responds to browser requests by supplying name-to-
address conversions. When it doesn’t know the answer, the resolver will ask
another name server for the information. When you type in a URL, your
browser sends a request to the closest name server. If that server has recently
had a request for the same host name, it will locate the information in its cache
and reply. If the name server is unfamiliar with the domain name, the resolver
will ask another nameserver. If that doesn’t work, the second server will ask
yet another - until it finds one that knows.
Once the information is located, it’s passed back to your browser, and
you are sent to the web site for the URL you entered. Usually this process
occurs quickly, but sometimes it takes several seconds. Occasionally, you will
get a dialog box that says the domain name doesn’t exist, even though you
know it does. This happens because of delays in one name server replying to
another, and your computer times out, dropping the connection. Often, if you
try again, you will get to the web site you are looking for on the second try.
This is because the nameserver with the information has had enough time to
reply, and your name server has now stored the information in its cache.
Hypertext
Hypertext is a text which contains links to other texts. The term was
invented by Ted Nelson around 1965. Hypertext is therefore usually non-linear
(as indicated below). Hypertext allows movement through a document in a
non-linear fashion. As such, it is a departure from a book and other “written”
material. The user can “navigate” through the use of links. These links may be
selected through a keyboard, a mouse, a touch screen or some other input
device. In all cases, a microprocessor is used. Hypertext documents are
prepared using an authoring tool. The most common authoring tool is probably
Hypertext Markup Language (HTML) However; there are other well known
authoring tools such as Author ware and Toolbox. Standard General Markup
Language that can also be used.
Technically speaking hypertext is a link you click on to get from one
page to another when surfing the internet (or an intranet). The pictures and
phrases that make up the links are called hypertext links. Any time you click on
something on a web site you are actively using hypertext. The hypertext we
want to look at here is a type of electronic genre for writing. We want to give
you some ideas of how you can use hypertext in the classroom and as a
publishing medium.
Hyperlinks
A hyperlink is a reference to another location within the existing HTML
document or in a new HTML document. The data of the HTML document or
object can be stored in file system file server on the Internet (referred to by
URLs), or any arbitrary location that can be referenced How a hyperlink is
presented to the user is up to the hyperlink container and the context of the
hyperlink. It is common for hyperlinks to be presented as colored, underlined
text, as hotspot regions on an image, or as pushbuttons. However, there are no
user interface requirements limiting the presentation of hyperlinks, although
guidelines suggest that they should be made obvious-via coloring, underlining,
or by changing the cursor or displaying tool tips when mouse over occurs. A
hyperlink is the same thing as a link. A link can be a picture or text or just
about anything on a web page. When something is a link, it simply means that
left clicking on it will lead you to a different place on the internet. This might
mean that you will be transferred to another page on the same web site. Or, it
might mean that you are transferred to a different site altogether. When a link is
embedded in text, the words composing the link are usually a different color
from the majority of text and most of the time, they are underlined.
URL (Universal Resource Locator)
Although a domain name provides a convenient way of referring to a
specific computer on the Internet, you rarely want to just connect to a
computer. More often, you want to retrieve information from a file on the
computer. To access a file on a computer connected to the Internet, you must
know the path to that file, known as its address. The addressing system
developed for this purpose is called a Uniform Resource Locator (URL).
What is a Domain Name?
Domains are the data that the Internet uses to identify specific “lots”
within the network. In their raw form, domains are numeric. I’m sure you’ve
seen this reflected in numeric URLs. Domain names are alphanumeric overlays
to the numeric component of a given domain. Essentially, they are the name of
the server on which the information resides. Systems Administrators get the
names from the Interknit how a name will be implemented are going to be up
to you and the server situation you are involved with. But, to some, having a
domain name is as much a part of their marketing strategy as other forms of
advertisement.
Domain Name Parts
Domains have two primary parts: the name and the suffix. Names can be
almost anything you want, although there are some character restrictions.
Typically, any combination of letters and numbers can be used to create the
name. This is followed by a suffix, which determines the type of organization
under which you register. General suffixes include
.com—Commercial organization (very common on the Web these days!)
.edu—Educational organization
.gov—Government institution
.mil—Military institution
.net—Network
.org—Organization
There are also country codes that fall into the suffix section of a domain.
Some examples include
.jp—Japan
.uk—Great Britain
.mx—Mexico
Search Engines
What are Search Engines?
Search engines are huge databases of web page files that have been
assembled automatically by machine. There are two types of search engines: ·
Individual. Individual search engines compile their own searchable databases
on the web. · Meta. Met searchers do not compile databases. Instead, they
search the databases of multiple sets of individual engines simultaneously It is
a program that searches documents for specified keywords and returns a list of
the documents where the keywords were found. Although search engine is
really a general class of programs, the term is often used to specifically
describe systems like Alta Vista and Excite that enable users to search for
documents on the World Wide Web and USENET newsgroups
Home Page
What is a Home Page?
For a Web user, the home page is the first Web page that is displayed
after starting a Web browser like Netscape’s Navigator or Microsoft’s Internet
Explorer. The browser is usually preset so that the home page is the first page
of the browser manufacturer. However, you can set it to open to any Web site.
For example, you can specify that “http://w.yahoo.com” or
“http://myweb.com” be your home page. You can also specify that there be no
home page (a blank space will be displayed) in which case you choose the first
page from your bookmark list or enter a Web address. For a Web site
developer, a home page is the first page presented when a user selects a site or
presence on the World Wide Web. The usual address for a Web site is the
home page address, although you can enter the address (Uniform Resource
Locator) of any page and have that page sent to you.
Web page images
Unless you are using a very new version of Internet Explorer as your
browser, saving a Web page will not include any images or animations that are
on the page - they are separate files. If the images on the Web page are an
important part of the content you wish to save to use offline, you must save the
images independently. To do so, right click the image (PC) or hold the mouse
down on the image (Mac) and select Save Picture as or Save Image As from
the pop-up menu. (If this option is not present in the pop-up menu, it is not a
standard image file that you can use offline - you are out of luck.) You will be
prompted with the Save dialog box as usual. It would be best to save the file
with the name and file type that is presented.
If you have saved the image file in the same location as the Web page
HTML file, there is a chance that you will see the image when you open the
Web page in your browser from your hard drive. If you do not see the image,
the Web page’s author must have used a different file hierarchy - you will have
to view the image separately from the Web page. Internet Explorer 5.0 will
give you an option to save the “Web page complete”, which means it will save
the page’s images with the HTML file for offline viewing.
Electronic mail, or e-mail as it is more commonly known, is a paperless
method of sending letters, notes and messages from you to someone else or
even many people at the same time via the Internet. Electronic mail is very fast
compared to the post office. Your messages usually only take seconds to arrive
at their destination. You can send messages anytime and the message will be
available whenever the other person wants to look at it - even in the middle of
the night. But perhaps the biggest advantage to using e-mail is that it is cheap,
especially when sending messages to other states or countries. Today, it costs
the same to send e-mail to someone around the corner as it does to send the
message to a friend in a foreign country.
Advantages of Electronic Mail System
There are many remarkable features that make electronic email far
ahead of other telecommunication technologies. Back in 1992, there were only
2% of Americans use electronic mail systems in the United States. The
percentage went up to 15% today. It went up seven times within 5 years,
according to a survey by consultants Forrester. Forrester also estimated that
within the next five years more than half of the American population will be
using e-mail. The lists below are few major advantages that encourage people
to use electronic mail over other similar communication tools. · It can send
pictures, sounds, spreadsheet, and long document.
It costs users nothing - probably just the cost of a local phone call. · It is
fast. It can be arrived anywhere in the world within a few minutes. · It makes
clear and concise communication, avoids the risk of verbal misunderstanding.
Electronic mail is actually a wonderful tool that helps individuals and
companies work faster and smarter when productivity and efficiency is the key.
All of these advantages have helped employers to choose electronic mail
system as their major communication tool for internal and external use.
Protocols used
Common Internet protocols that enable you to access the Internet are
Hypertext Transfer Protocol (HTTP), HTTP Secure (HTTPS), File Transfer
Protocol (FTP), Simple Mail Transfer Protocol (SMTP), and Network News
Transfer Protocol (NNTP). In addition, Hypertext Markup Language (HTML)
and Dynamic HTML (DHTML) specify the formats of pages displayed on the
Web.
· HTTP
HTTP is a convention for sending messages from a server to a client by
using TCP/IP. HTTP communications are in plain text and not encrypted.
· HTTPS
HTTPS enables you to make a secure Web server connection by using
Secure Sockets Layer (SSL). SSL is an encryption technology that enables a
secure connection between a server and a client. The URLs for Web pages that
require an SSL connection start with https://.
· FTP
FTP enables you to transfer files between two computers on a network.
· SMTP
SMTP enables you to send e-mail over the Internet.
· NNTP
NNTP enables you to post, distribute, and retrieve messages on Internet
and intranet newsgroups.
· HTML
HTML is the standard language for creating and formatting Web pages.
HTML defines how text appears when viewed in a Web browser.
Mail Server
A mail server is a computer, or a software package, that provides a mail
service to client software running on other computers. There are main two
types of mail servers.
POP3 (Incoming) E-mail Server
Post Office Protocol 3 is the most recent version of a standard protocol
for receiving email. POP3 is a client/server protocol in which e-mail is received
and held for you by your Internet server. Periodically, you (or your client e-
mail receiver) check your mail-box on the server and download any mail.
POP3 is built into the Netscape and Microsoft Internet Explorer browsers.
POP3 accounts allow clients to have a private e-mail address where they can
exchange email with anyone they wish at anytime. Each POP3 email account
comes with its own login and password. The login is set by the characters
preceding the at sign “@” in the e-mail address. The password is determined by
the client when the POP3 account is setup.
SMTP (Outgoing) E-mail Servers
The ability to provide Email services to clients includes two critical
functions: SMTP and POP3. Together, they provide the means for clients to
send out-going mails and check for new incoming mail, respectively. SMTP
service is the side of Email that allows clients to send out-going E-mail
messages to any valid Email address. The SMTP server performs two basic but
important functions. First, it verifies that anyone attempting to send outgoing
E-mails through the SMTP server has the right to do so. Secondly, it sends the
out-going mails and if undeliverable, sends the message back to the sender.
You need to configure your Email client so that it knows what SMTP server to
use for sending outgoing E-mail messages. In order to send mails through the
proper SMTP servers, configure your e-mail client to access the SMTP (Out-
going Mails) Server: yourdomain.com.
Mail Addresses
Definition of Email Address and ID Terms
University Email Address
Address appearing in any public paper or electronic directories. This
address is used to protect the User ID from public view. Default format of this
address is ‘first name’.’ last name’@uky.edu. The portion of this address
before the ‘@’ may be modified by the owner.
Mailbox
Email system address to which email is redirected from the University
Email Address, stored and read by a user. Default format of this address is
‘User ID or other’@’email system identifier’.uky.edu. The ‘email system
identifier’ is not included in U-Connect accounts.
User ID:
This ID is used in conjunction with a password to permit a user to log
into an email system and access email in their mailbox.
Common Features in Netscape Communicator and Internet
Explorer
Internet Explorer and Netscape Communicator
Internet Explorer has migrated to the forefront as the preferred browser
because of the various applications used across the Internet by the University
System. Such programs as the PeopleSoft applications and various medical
programs used in the hospital enterprise require that Internet Explorer be used.
One thing to note is that Internet Explorer is installed by an automated process
that is established by ITS. For that reason, some functions are not accessible.
For example, endeavoring to change some the Options in Internet Explorer will
be impossible because the fields are grayed-out. The centralized installation
will also force some characteristics onto your workstation that have proven to
be an inconvenience to users. The only resolution is to make Internet Explorer
your default browser. The instructions for doing this are provided below.
Unfortunately, Internet Explorer is essentially a proprietary Microsoft product
and is not fully compliant with many of the international programming
standards used at many web sites. Netscape is often required to access some of
the features used at web sites. Until the compatibility issues are resolved, both
browsers will need to be supported and provided to users upon request.
The discussions presented below are frequent issues for users and
support personnel.
IT support will usually provide any assistance that is needed to resolve
compatibility issues between Internet Explorer and Netscape, but if help is not
immediately available the information below may prove useful.
Internet Explorer
How to Make Internet Explorer Your Default Browser
Follow these steps:
� Click on the Start button
� Select Settings
� Select Control Panel
� Select Internet Options
� Select the Program tab
� Check the box at the base of them window labeled “Internet Explorer
should check to see whether ....”
This usually does the trick. The next time Internet Explorer is activated,
it should present a query of whether you wish it to be your default browser.
Testing, however, has shown that this does not always work.
Conflicts between Internet Explorer and Netscape
Communicator
A recent update to Internet Explorer apparently generated a rash of lock-
ups whenever users attempted to open Netscape Communicator. Regardless of
what Microsoft says under oath, Internet Explorer is installed and updated by
Microsoft in a manner that seizes control of the Internet browser functions.
This causes considerable confusion for users and generates considerable cost in
supporting Netscape. As a consequence, the best solution is to let Internet
Explorer be your default browser and to install Netscape only if it is necessary
to utilize specific web pages.
Step#1, making Internet Explorer your default browser, is discussed
above. This usually works but there are cases where it does not work. If it fails,
proceed to Step #2.
Step #2 is to uninstall the Netscape program. This will clear out all
remnants of the Netscape program. To do so, follow these steps:
� Make certain all Internet browsers are closed.
� Go to the Department Applications/Setups/Applications menu.
� Click on the item titled “Netscape Communicator 4.75 Pre-Install.”
Running this program will backup your personal settings for Netscape
and clean out all Netscape program files and registry settings.
� Re-start your PC.
� After logging back onto the network, open Internet Explorer. If it asks
for you to make it the default browser, click “Yes.”
� To test how Internet Explorer will work, you may wish to bring up an e-
mail message that listed a website, click on that web site and see if
Internet Explorer is presented automatically.
Step #3 is necessary only if you wish to have Netscape re-installed.
� Make certain that all Internet browsers are closed.
� Return to the Department Applications/Setups/Applications menu.
� Run the item titled “Netscape Communicator 4.75”. This should re-load
a clean set of files for Netscape and refresh the registry.
� Open Netscape. A “profile manager” will be presented.
� Select “Default” and then press the “Start Communicator” button.
“Default” is the standard settings used by Netscape that accesses your
personal settings located in your personal directory on the server.
Importing Netscape Bookmarks
A common problem with moving to Internet Explorer is incorporating
the bookmarks you use in Netscape. This is fairly easy to do. Follow these
steps:
� Open Internet Explorer
� Select the “File” menu.
� Select “Import and Export”
� A window will be presented explaining what you can do with this
utility. Click the “Next” key.
� Select “Import Favorites.”
� Click the dot that says to Import from File or Address.
� File in the blank with the following: J:\Netscape\bookmark.htm
� For the destination, select the folder that has your login ID on it.
� Once the installation is complete your bookmarks will be imported into
the folder under your login ID.
Managing the Favorites Folder
The Favorites Folder in Internet Explorer is, unfortunately, a hodge-
podge of functions that could prove somewhat confusing. The oddity about
Internet Explorer is that it is the only program where personal settings do not
“roam.” In other words, the Favorites folder does not automatically copy to
your personal directory on our server and if you move to a different computer
your bookmarks will be missing. The following solutions have been employed
to solve that riddle. · First, some of the folders are imported automatically from
ITS. Most of these folders will pertain to commonly used University Hospital
web sites. Special attention should be provided to the folder titled “University
of Missouri Healthcare — Resources.” In it you will find several websites that
will provide useful services · The Department supplies an additional folder with
your login ID. This is where you should install your personal bookmarks.
� On a daily basis a program is executed that will endeavor to update your
personal bookmarks to your personal directory. The only bookmarks
updated, however, are those which reside under your ID.
� Feel free to remove folders that belong to other people. Their bookmarks
should be backed up into their personal directories.
� Research has been completed and testing will commence in late October
that will integrate the Favorites list into your personal profile. If tests
prove successful, management of Favorites should be much easier and
more intuitive.
Web Design Concerns
File Names
Web page editors are rather familiar with creating “hotlinks” to other
documents. You may wish to note, however, that Microsoft’s intuitive
“features” that are often included with Internet Explorer and other web design
tools can often create some problems with your final web document. One
particular area is file naming. The Internet is based on UNIX, a network
operating system. From UNIX, an internationally agreed standard of
programming was devised to make it possible to read documents, tables, and
images on any computer in the world. That standard was called HTML. That
standard does not permit spaces in file names. For example, if you create a
document in Microsoft Word and title it “Goals for 2001”, the only thing that
HTML or UNIX will read is “Goals”. The result is a failed hotlink. To correct
that problem, you must label the file as “Goals_for_2001”, replacing the space
with an underscore.
Writing effective Mail Messages
E-mail is a prized tool for the small entrepreneur. It allows you to
communicate quickly and frequently with your customer. It doesn’t matter that
your competitor can afford a fancy logo and expensive stationery. E-mail puts
you on an even footing. Without graphics or engraving to enhance your
message, what you say and how you say it matters even more than in print
communication. But because e-mail is so easy to send, and because as a harried
owner of a small business you feel pressured to respond immediately, you often
dash off a response on the fly. How many times have you clicked on “send”
and then remembered a couple of points you forgot to mention? Or did you
send a rambling message, giving your client the task of sorting it out? Did you
think your spelling didn’t matter? After all, “it’s only e-mail!” It matters a lot.
Your well-heeled competitor has the stature of his organization to back him up.
His misspellings will be chalked up to “too busy to spell check.” Your
misspellings and unorganized messages will call your competence into
question. Does your inattention to spelling reflect a similar disregard for
customer service? If your message is ill-conceived, can your product be any
better? When you write e-mail messages, remember your client will judge you
by what you say and how you say it. Don’t let your writing give your
customers a reason to turn to your competitor. Here are some guidelines to
enable you to write e-mail like the Fortune 500 pros.
THE NUMBTHE NUMBTHE NUMBTHE NUMBER SYSTEMSER SYSTEMSER SYSTEMSER SYSTEMS
The reason that "hex" and octal are popular in computing is that it's easy to
translate to and from the binary system that computers really use. People use
decimal primarily because they have ten fingers, but it's just not that convenient
to switch back and forth from 10011010010 to 1234. It IS convenient to
convert to 4D2 (hex) or 2322 (octal).
The numbers from decimal 0 through 15 in decimal, binary, octal, and
hexadecimal form are listed below.
DECIMAL BINARY OCTAL HEXA -DECIMAL
0 0 0 0
1 1 1 1
2 10 2 2
3 11 3 3
4 100 4 4
5 101 5 5
6 110 6 6
7 111 7 7
8 1000 10 8
9 1001 11 9
10 1010 12 A
11 1011 13 B
12 1100 14 C
13 1101 15 D
14 1110 16 E
15 1111 17 F
Binary
Binary describes a numbering scheme in which there are only two possible
values for each digit: 0 and 1. The term also refers to any digital
encoding/decoding system in which there are exactly two possible states. In
digital data memory, storage, processing, and communications, the 0 and 1
values are sometimes called "low" and "high," respectively.
Binary numbers look strange when they are written out directly. This is
because the digits' weight increases by powers of 2, rather than by powers of
10. In a digital numeral, the digit furthest to the right is the "ones" digit; the
next digit to the left is the "twos" digit; next comes the "fours" digit, then the
"eights" digit, then the "16s" digit, then the "32s" digit, and so on. The decimal
equivalent of a binary number can be found by summing all the digits.
For example, the binary 10101 is equivalent to the decimal 1 + 4 + 16 = 21
DECIMAL = 21 64 32 16 8 4 2 1
BINARY = 10101 0 0 1 0 1 0 1
Hexadecimal
Hexadecimal describes a base-16 number system. That is, it describes a
numbering system containing 16 sequential numbers as base units (including 0)
before adding a new position for the next number. (Note that we're using "16"
here as a decimal number to explain a number that would be "10" in
hexadecimal.) The hexadecimal numbers are 0-9 and then use the letters A-F.
We show the equivalence of binary, decimal, and hexadecimal numbers in the
table below.
Hexadecimal is a convenient way to express binary numbers in modern
computers in which a byte is almost always defined as containing eight binary
digits. When showing the contents of computer storage (for example, when
getting a core dump of storage in order to debug a new computer program or
when expressing a string of text characters or a string of binary values in
coding a program or HT ML page), one hexadecimal digit can represent the
arrangement of four binary digits. Two hexadecimal digits can represent eight
binary digits, or a byte.
Octal
Octal (pronounced AHK-tuhl, from Latin octo or "eight") is a term that
describes a base-8 number system. An octal number system consists of eight
single-digit numbers: 0, 1, 2, 3, 4, 5, 6, and 7. the number after 7 is 10. The
number after 17 is 20 and so forth.
In computer programming, the octal equivalent of a binary number is
sometimes used to represent it because it is shorter.
CHARACTERS AND DECIMAL, BINARY, ASCII, CHARACTERS AND DECIMAL, BINARY, ASCII, CHARACTERS AND DECIMAL, BINARY, ASCII, CHARACTERS AND DECIMAL, BINARY, ASCII,
EBCDIC VALUEEBCDIC VALUEEBCDIC VALUEEBCDIC VALUE
Capital Letters
Characters Decimal Binary ASCII EBCDIC
A 65 1000001 1000001 01000001
B 66 1000010 1000010 01000010
C 67 1000011 1000011 01000011
D 68 1000100 1000100 01000100
E 69 1000101 1000101 01000101
F 70 1000110 1000110 01000110
G 71 1000111 1000111 01000111
H 72 1001000 1001000 01001000
I 73 1001001 1001001 01001001
J 74 1001010 1001010 01001010
K 75 1001011 1001011 01001011
L 76 1001100 1001100 01001100
M 77 1001101 1001101 01001101
N 78 1001110 1001110 01001110
O 79 1001111 1001111 01001111
P 80 1010000 1010000 01010000
Q 81 1010001 1010001 01010001
R 82 1010010 1010010 01010010
S 83 1010011 1010011 01010011
T 84 1010100 1010100 01010100
U 85 1010101 1010101 01010101
V 86 1010110 1010110 01010110
W 87 1010111 1010111 01010111
X 88 1011000 1011000 01011000
Y 89 1011001 1011001 01011001
Z 90 1011010 1011010 01011010
CHARACTERS AND DECIMAL, BINARY, ASCII, CHARACTERS AND DECIMAL, BINARY, ASCII, CHARACTERS AND DECIMAL, BINARY, ASCII, CHARACTERS AND DECIMAL, BINARY, ASCII,
EBCDIC VALUEEBCDIC VALUEEBCDIC VALUEEBCDIC VALUE
Small Letters
Characters Decimal Binary ASCII EBCDIC
a 97 1100001 1100001 01100001
b 98 1100010 1100010 01100010
c 99 1100011 1100011 01100011
d 100 1100100 1100100 01100100
e 101 1100101 1100101 01100101
f 102 1100110 1100110 01100110
g 103 1100111 1100111 01100111
h 104 1101000 1101000 01101000
i 105 1101001 1101001 01101001
j 106 1101010 1101010 01101010
k 107 1101011 1101011 01101011
l 108 1101100 1101100 01101100
m 109 1101101 1101101 01101101
n 110 1101110 1101110 01101110
o 111 1101111 1101111 01101111
p 112 1110000 1110000 01110000
q 113 1110001 1110001 01110001
r 114 1110010 1110010 01110010
s 115 1110011 1110011 01110011
t 116 1110100 1110100 01110100
u 117 1110101 1110101 01110101
v 118 1110110 1110110 01110110
w 119 1110111 1110111 01110111
x 120 1111000 1111000 01111000
y 121 1111001 1111001 01111001
z 122 1111010 1111010 01111010
SHORTCUT KEYSSHORTCUT KEYSSHORTCUT KEYSSHORTCUT KEYS
General keyboard shortcuts
Press To ALT+ENTER View properties for the selected item.
ALT+Enter Displays the properties of the selected object.
ALT+ESC Cycle through items in the order they were opened.
ALT+F4 Close the active item, or quit the active program.
ALT+SPACEBAR Opens the shortcut menu for the active window.
ALT+SPACEBAR Display the System menu for the active window.
ALT+TAB Switch between open items.
ALT+Underlined letter in a menu name
Display the corresponding menu.
BACKSPACE View the folder one level up in My Computer or Windows Explorer.
CTRL while dragging an item
Copy selected item.
CTRL+A Select all.
CTRL+C Copy.
CTRL+DOWN ARROW Move the insertion point to the beginning of the next paragraph.
CTRL+ESC Display the Start menu.
CTRL+F4 Close the active document in programs that allow you to have multiple documents open simultaneously.
CTRL+LEFT ARROW Move the insertion point to the beginning of the previous word.
CTRL+RIGHT ARROW Move the insertion point to the beginning of the next word.
CTRL+SHIFT while dragging an item
Create shortcut to selected item.
CTRL+SHIFT with any of the arrow keys
Highlight a block of text.
CTRL+UP ARROW Move the insertion point to the beginning of the previous paragraph.
CTRL+V Paste.
CTRL+X Cut.
CTRL+Z Undo.
DELETE Delete.
ESC Cancel the current task.
F10 Activate the menu bar in the active program.
F2 Rename selected item.
F3 Search for a file or folder.
F4 Display the Address bar list in My Computer or Windows Explorer.
F5 Refresh the active window.
F6 Cycle through screen elements in a window or on the desktop.
LEFT ARROW Open the next menu to the left, or close a submenu.
RIGHT ARROW Open the next menu to the right, or open a submenu.
SHIFT when you insert a CD into the CD-ROM drive
Prevent the CD from automatically playing.
SHIFT with any of the arrow keys
Select more than one item in a window or on the desktop, or select text within a document.
SHIFT+DELETE Delete selected item permanently without placing the item in the Recycle Bin.
SHIFT+F10 Display the shortcut menu for the selected item.
Underlined letter in a command name on an open menu
Carry out the corresponding command.
Dialog box keyboard shortcuts
Press To CTRL+TAB Move forward through tabs.
CTRL+SHIFT+TAB Move backward through tabs.
TAB Move forward through options.
SHIFT+TAB Move backward through options.
ALT+Underlined letter
Carry out the corresponding command or select the corresponding option.
ENTER Carry out the command for the active option or button.
SPACEBAR Select or clear the check box if the active option is a check box.
Arrow keys Select a button if the active option is a group of option buttons.
F1 Display Help.
F4 Display the items in the active list.
BACKSPACE Open a folder one level up if a folder is selected in the Save As or Open dialog box.
Natural keyboard shortcuts You can use the following keyboard shortcuts with a Microsoft Natural Keyboard or any other compatible keyboard that includes the Windows logo
key ( ) and the Application key ( ).
Press To Display or hide the Start menu.
+BREAK Display the System Properties dialog box.
+D Show the desktop.
+M Minimize all windows.
+Shift+M Restores minimized windows.
+E Open My Computer.
+F Search for a file or folder.
CTRL+ +F Search for computers.
+F1 Display Windows Help.
+ L Lock your computer if you are connected to a network domain, or switch users if you are not connected to a network domain.
+R Open the Run dialog box.
Display the shortcut menu for the selected item.
+U Open Utility Manager.
Accessibility keyboard shortcuts
Press To Right SHIFT for eight seconds Switch Filter Keys on and off.
Left ALT +left SHIFT +PRINT SCREEN
Switch High Contrast on and off.
Left ALT +left SHIFT +NUM LOCK
Switch MouseKeys on and off.
SHIFT five times Switch Sticky Keys on and off.
NUM LOCK for five seconds Switch Toggle Keys on and off.
+U Open Utility Manager.
Windows Explorer keyboard shortcuts
Press To END Display the bottom of the active window.
HOME Display the top of the active window.
NUM LOCK+ASTERISK on numeric keypad (*)
Display all subfolders under the selected folder.
NUM LOCK+PLUS SIGN on Display the contents of the selected
numeric keypad (+) folder.
NUM LOCK+MINUS SIGN on numeric keypad (-)
Collapse the selected folder.
LEFT ARROW Collapse current selection if it's expanded or select parent folder.
RIGHT ARROW Display current selection if it's collapsed, or select first subfolder.
WHAT IS DOS?WHAT IS DOS?WHAT IS DOS?WHAT IS DOS?
Microsoft DOS (Disk Operating System) is a command line user
interface. MS-DOS 1.0 was released in 1981 for IBM computers and the latest
version of MS -DOS is MS-DOS 6.22, which was released in 1994. While MS
-DOS is not commonly used by itself today, it still can be accessed from every
version of Microsoft Windows by clicking Start / Run and typing "command"
or by typing "CMD" in Windows NT, Windows 2000 or Windows XP.
Differences between DOS Internal and External
Commands
Internal commands
A command that is stored in the system memory and loaded from the
command.com. Below are examples of internal MS -DOS commands currently
listed in the Computer dos database.
ASSOC BREAK CALL
CD CHDIR CLS
COLOR COPY CTTY
DATE DEL DIR
DRIVPARM ECHO ERASE
EXIT FOR LH
LOADHIGH LOCK MD
MKDIR MOVE PATH
PAUSE PROMPT RD
REN RENAME RMDIR
SET SWITCHES TIME
TYPE
External command
A MS-DOS command that is not included in command.com. External
commands are commonly external either because it requires large requirements
and/or are not commonly used commands. Below are examples of MS-DOS
external commands currently listed in the Computer dos database.
APPEND ARP ASSIGN
AT ATTRIB CACLS
CHCP CHKDSK CHKNTFS
CHOICE COMP COMPACT
CONVERT DEBUG DEFRAG
DELTREE DISKCOMP DISKCOPY
DOSKEY DOSSHELL EDIT
EDLIN EXPAND EXTRACT
FASTHELP FC FDISK
FIND FORMAT GRAFTABL
HELP IPCONFIG LABEL
LOADFIX MEM MODE
MORE MSAV MSCDEX
MSCDEXNT MSD NBTSTAT
NET NETSTAT NLSFUNC
NSLOOKUP PATHPING PING
POWER PRINT ROUTE
SCANDISK SCANREG SETVER
SHARE SHUTDOWN SMARTDRV
SORT SUBST SYS
TRACERT TREE UNDELETE
UNFORMAT
DOS COMMANDS AND EXPLANATIONDOS COMMANDS AND EXPLANATIONDOS COMMANDS AND EXPLANATIONDOS COMMANDS AND EXPLANATION
No Command Name Explanation
01. ASSOC Displays or modifies file extension associations.
02. AT Schedules commands and programs to run on a
computer.
03. ATTRIB Displays or changes file attributes.
04. BREAK Sets or clears extended CTRL+C checking.
05. CACLS Displays or modifies access control lists (ACLs) of
files.
06. CALL Calls one batch program from another.
07. CD Displays the name of or changes the current
directory.
08. CHCP Displays or sets the active code page number.
09. CHDIR Displays the name of or changes the current
directory.
10. CHKDSK Checks a disk and displays a status report.
11. CHKNTFS Displays or modifies the checking of disk at boot
time.
12. CLS Clears the screen.
13. CMD Starts a new instance of the Windows command
interpreter.
14. COLOR Sets the default console foreground and background
colors.
15. COMP Compares the contents of two files or sets of files.
16. COMPACT Displays or alters the compression of files on NTFS
partitions.
17. CONVERT Converts FAT volumes to NTFS. You cannot
convert the current drive.
18. COPY Copies one or more files to another location.
19. DATE Displays or sets the date.
20. DEL Deletes one or more files.
21. DIR Displays a list of files and subdirectories in a
directory.
22. DISKCOMP Compares the contents of two floppy disks.
23. DISKCOPY Copies the contents of one floppy disk to another.
24. DOSKEY Edits command lines, recalls Windows commands,
and creates macros.
25. ECHO Displays messages, or turns command echoing on or
off.
26. ENDLOCAL Ends localization of environment changes in a batch
file.
27. ERASE Deletes one or more files.
28. EXIT Quits the CMD.EXE program (command
interpreter).
29. FC Compares two files or sets of files, and displays the
differences between them.
30. FIND Searches for a text string in a file or files.
31. FINDSTR Searches for strings in files.
32. FOR Runs a specified command for each file in a set of
files.
33. FORMAT Formats a disk for use with Windows.
34. FTYPE Displays or modifies file types used in file extension
associations.
35. GOTO Directs the Windows command interpreter to a
labeled line in a batch program.
36. GRAFTABL Enables Windows to display an extended character
set in graphics mode.
37. HELP Provides Help information for Windows commands.
38. IF Performs conditional processing in batch programs.
39. LABEL Creates, changes, or deletes the volume label of a
disk.
40. MD Creates a directory.
41. MKDIR Creates a directory.
42. MODE Configures a system device.
43. MORE Displays output one screen at a time.
44. MOVE Moves one or more files from one directory to
another directory.
45. PATH Displays or sets a search path for executable files.
46. PAUSE Suspends processing of a batch file and displays a
message.
47. POPD Restores the previous value of the current directory
saved by PUSHD.
48. PRINT Prints a text file.
49. PROMPT Changes the Windows command prompt.
50. PUSHD Saves the current directory then changes it.
51. RD Removes a directory.
52. RECOVER Recovers readable information from a bad or
defective disk.
53. REM Records comments (remarks) in batch files or
CONFIG.SYS.
54. REN Renames a file or files.
55. RENAME Renames a file or files.
56. REPLACE Replaces files.
57. RMDIR Removes a directory.
58. SET Displays, sets, or removes Windows environment
variables.
59. SETLOCAL Begins localization of environment changes in a
batch file.
60. SHIFT Shifts the position of replaceable parameters in
batch files.
61. SORT Sorts input.
62. START Starts a separate window to run a specified program
or command.
63. SUBST Associates a path with a drive letter.
64. TIME Displays or sets the system time.
65. TITLE Sets the window title for a CMD.EXE session.
66. TREE Graphically displays the directory structure of a
drive or path.
67. TYPE Displays the contents of a text file.
68. VER Displays the Windows version.
69. VERIFY Tells Windows whether to verify that your files are
written correctly to a disk.
70. VOL Displays a disk volume label and serial number.
71. XCOPY Copies files and directory trees.
MODEM ERROR MESSAGESMODEM ERROR MESSAGESMODEM ERROR MESSAGESMODEM ERROR MESSAGES
No Error Messages
600 An operation is pending.
601 An invalid port handle was detected.
602 The specified port is already open.
603 The caller's buffer is too small.
604 Incorrect information was specified.
605 The port information cannot be set.
606 The specified port is not connected.
607 An invalid event is detected.
608 A device was specified that does not exist.
609 The device type was specified that does not exist.
610 An invalid buffer was specified.
611 A route was specified that is not available.
612 A route was specified that is not allocated.
613 An invalid compression was specified.
614 There were insufficient buffers available.
615 The specified port was not found.
616 An asynchronous request is pending.
617 The modem is already disconnecting.
618 The specified port is not open.
619 The specified port is not connected.
620 No endpoints could be determined.
621 The system could not open the phonebook.
622 The system could not load the phonebook.
623 The system could not find the phonebook entry for this connection.
624 The system could not update the phonebook file.
No Error Messages
625 The system found invalid information in the phonebook.
626 A string could not be loaded.
627 A key could not be found.
628 The connection was closed.
629 The connection was closed by the remote computer.
630 The modem was disconnected due to hardware failure.
631 The user disconnected the modem.
632 An incorrect structure size was detected.
633 The modem is already in use or is not configured for dialing out.
634 Your computer could not be registered on the remote network.
635 There was an unknown error.
636 The device attached to the port is not the one expected.
637 A string was detected that could not be converted.
638 The request has timed out.
639 No asynchronous net is available.
640 An error has occurred involving NetBIOS.
641 The server cannot allocate NetBIOS resources needed to support the
client.
642 One of your computer's NetBIOS names is already registered on the
remote network.
643 A network adapter at the server failed.
644 You will not receive network message popups.
645 There was an internal authentication error.
646 The account is not permitted to log on at this time of day.
647 The account is disabled.
648 The password for this account has expired.
649 The account does not have permission to dial in.
650 The remote access server is not responding.
651 The modem has reported an error.
No Error Messages
652 There was an unrecognized response from the modem.
653 A macro required by the modem was not found in the device .INF file
section.
654 A command or response in the device .INF file section refers to an
undefined macro.
655 The <MESSAGE> macro was not found in the device .INF file section.
656 The <DEFAULTOFF> macro in the device .INF file section contains an undefined macro.
657 The device .INF file could not be opened.
658 The device name in the device .INF or media .INI file is too long.
659 The media .INI file refers to an unknown device name.
660 The device .INF file contains no responses for the command.
661 The device .INF file is missing a command.
662 There was an attempt to set a macro not listed in the device .INF file
section.
663 The media .INI file refers to an unknown device type.
664 The system has run out of memory.
665 The modem is not properly configured.
666 The modem is not functioning.
667 The system was unable to read the media .INI file.
668 The connection was terminated.
669 The usage parameter in the media .INI file is invalid.
670 The system was unable to read the section name from the media .INI
file.
671 The system was unable to read the device type from the media .INI file.
672 The system was unable to read the device name from the media .INI file.
673 The system was unable to read the usage from the media .INI file.
674 The system was unable to read the maximum connection BPS rate from
the media .INI file.
No Error Messages
675 The system was unable to read the maximum carrier connection speed
from the media .INI file.
676 The phone line is busy.
677 A person answered instead of a modem.
678 There was no answer.
679 The system could not detect the carrier.
680 There was no dial tone.
681 The modem reported a general error.
691 Access was denied because the user name and/or password was invalid
on the domain.
692 There was a hardware failure in the modem.
695 The state machines are not started.
696 The state machines are already started.
697 The response looping did not complete.
699 The modem response caused a buffer overflow.
700 The expanded command in the device .INF file is too long.
701 The modem moved to a connection speed not supported by the COM
driver.
703 The connection needs information from you, but the application does not
allow user interaction.
704 The callback number is invalid.
705 The authorization state is invalid.
707 There was an error related to the X.25 protocol.
708 The account has expired.
709 There was an error changing the password on the domain. The password
might have been too short or might have matched a previously used
password.
710 Serial overrun errors were detected while communicating with the
modem.
No Error Messages
711 The Remote Access Service Manager could not start. Additional
information is provided in the event log.
712 The two-way port is initializing. Wait a few seconds and redial.
713 No active ISDN lines are available.
714 No ISDN channels are available to make the call.
715 Too many errors occurred because of poor phone line quality.
716 The remote access service IP configuration is unusable.
717 No IP addresses are available in the static pool of remote access service
IP addresses.
718 The connection timed out waiting for a valid response from the remote
computer.
719 The connection was terminated by the remote computer.
721 The remote computer is not responding.
722 Invalid data was received from the remote computer. This data was
ignored.
723 The phone number, including prefix and suffix, is too long.
726 The IPX protocol cannot be used for dial-out on more than one modem
at a time.
728 The system cannot find an IP adapter.
729 SLIP cannot be used unless the IP protocol is installed.
731 The protocol is not configured.
732 Your computer and the remote computer could not agree on PPP control
protocols.
733 Your computer and the remote computer could not agree on PPP control
protocols.
734 The PPP link control protocol was terminated.
735 The requested address was rejected by the server.
736 The remote computer terminated the control protocol.
737 Loop back detected.
No Error Messages
738 The server did not assign an address.
739 The authentication protocol required by the remote server cannot use the
stored password. Redial, entering the password explicitly.
740 An invalid dialing rule was detected.
741 The local computer does not support the required data encryption type.
742 The remote computer does not support the required data encryption type.
743 The remote server requires data encryption.
751 The callback number contains an invalid character. Only the following
characters are allowed: 0 to 9, T, P, W, (,), -, @, and space.
752 A syntax error was encountered while processing a script.
753 The connection could not be disconnected because it was created by the
multi-protocol router.
754 The system could not find the multi-link bundle.
755 The system cannot perform automated dial because this entry has a
custom dialer specified.
756 This connection is already being dialed.
757 Remote access services could not be started automatically. Additional
information is provided in the event log.
758 Internet Connection Sharing is already enabled on the connection.
760 An error occurred while routing capabilities were being enabled.
761 An error occurred while Internet Connection Sharing was being enabled
for the connection.
763 Internet Connection Sharing cannot be enabled. There are two or more
LAN connections in addition to the connection to be shared.
764 No smart card reader is installed.
765 Internet Connection Sharing cannot be enabled. A LAN connection is
already configured with the IP address required for automatic IP
addressing.
No Error Messages
767 Internet Connection Sharing cannot be enabled. The LAN connection
selected on the private network has more than one IP address configured.
Reconfigure the LAN connection with a single IP address before
enabling Internet Connection Sharing.
768 The connection attempt failed because of failure to encrypt data.
769 The specified destination is not reachable.
770 The remote machine rejected the connection attempt.
771 The connection attempt failed because the network is busy.
772 The remote computer's network hardware is incompatible with the type
of call requested.
773 The connection attempt failed because the destination number has
changed.
774 The connection attempt failed because of a temporary failure. Try
connecting again.
775 The call was blocked by the remote computer.
776 The call could not be connected because the destination has invoked the
Do Not Disturb feature.
777 The connection attempt failed because the modem on the remote
computer is out of order.
778 It was not possible to verify the identity of the server.
780 An attempted function is not valid for this connection.
783 Internet Connection Sharing cannot be enabled. The LAN connection
selected as the private network is either not present, or is disconnected
from the network. Please ensure that the LAN adapter is connected
before enabling Internet Connection Sharing.
784 You cannot dial using this connection at logon time, because it is
configured to use a user name different than the one on the smart card. If
you want to use it at logon time, you must configure it to use the user
name on the smart card.
No Error Messages
785 You cannot dial using this connection at logon time, because it is not
configured to use a smart card. If you want to use it at logon time, you
must edit the properties of this connection so that it uses a smart card.
788 The L2TP connection attempt failed because the security layer could not
negotiate compatible parameters with the remote computer.
789 The L2TP connection attempt failed because the security layer
encountered a processing error during initial negotiations with the
remote computer.
791 The L2TP connection attempt failed because security policy for the
connection was not found.
792 The L2TP connection attempt failed because security negotiation timed
out.
793 The L2TP connection attempt failed because an error occurred while
negotiating security.
794 The Framed Protocol RADIUS attribute for this user is not PPP.
795 The Tunnel Type RADIUS attribute for this user is not correct.
796 The Service Type RADIUS attribute for this user is neither Framed nor
Callback Framed.
797 A connection to the remote computer could not be established because
the modem was not found or was busy.
799 Internet Connection Sharing (ICS) cannot be enabled due to an IP
address conflict on the network. ICS requires the host be configured to
use 192.168.0.1. Please ensure that no other client on the network is
configured to use 192.168.0.1.
800 Unable to establish the VPN connection. The VPN server may be
unreachable, or security parameters may not be configured properly for
this connection.
ABBREVIATIONABBREVIATIONABBREVIATIONABBREVIATION
01. A/L Alphanumeric
02. ABC Atanasoft Berry Computer
03. ACE Automatic Computing Engine
04. ACK Acknowledgement
05. ADC Analog to Digital Converter
06. ADSL Asynchronous Digital Subscriber Loop
07. AI Artificial Intelligence
08. ALGOL Algorithmic language
09. ALU Arithmetic and Logic Unit
10. ANSI American National Standards Institution
11. AOL America On Line
12. APL A Programming Language
13. ARPANET Advanced Research Project
14. AS Auxiliary Storage
15. ASCC Automatic Sequence – Controlled Calculator
16. ASCII American Standard Cord for Information Interchange
17. ATM Automatic Teller Machines
18. ATM Asynchronous Transfer Mode
19. BA Binary Address
20. BASIC Beginner’s All-Purpose Symbolic Instruction Code
21. BC Binary Code
22. BCD Binary Coded Decimal
23. BCDIC Binary Coded Decimal Interchange Code
24. BCO Binary Coded Octal
25. BIS Business Information System
26. BIT Binary Digit
27. BPS Bit Transaction Processing
28. BPS Bits Per Second
29. CAD Computer Aided Design
30. CAE Computer Aided Engineering
31. CAI Computer Aided Instruction
32. CALS Computer Aided Logistic and Support
33. CAM Computer Aided Manufacturing
34. CAM Computer Assisted Manufacture
35. CAR Computer Assisted Retrieval
36. CASE Computer Aided Software Engineering
37. CBASIC A Complier Vision Of BASIC
38. CCITT Consultative Committee For International Telephony
And Telegraphy
39. CCTTT Acronym For International Committee or Telephone
And Telegraphy
40. CCU Central Control Unit
41. CD Compact Disk
42. CDE Channel Definition Format
43. CDMA Common Division Multiple Access
44. CD-ROM Compact Disk-Read Only Memory
45. CERN Center For European Nuclear Research
46. CGA Color Graphic Adaptor
47. CGI Computer Galway Interface
48. CGI Computer Galway Interface
49. CHS Character per Second
50. CIM Computer Input on Microfilm
51. CIM Chief Information Officer
52. CIP Current Instruction Register
53. CISC Complex Instruction Set Computer
54. CIU Computer Interface Unit
55. CMOS Complimentary Metal Oxide Semiconductor
56. COBOL Common Business Oriented Language
57. CODASYL Conference For Data Systems Language
58. CODEC Coder /Decoder
59. COL Computer Oriented Language
60. COM Computer Output on Microfilm
61. CPS Character Per Second / Cycles Per Second
62. CPU Control Processing Unit
63. CR Character Recognition
64. CRT Cathode Ray Tube
65. CSCW Computer Supported Co-operative Work
66. CSMACD Carrier Sense Multiple Access With Collision Detector
67. CU Control Unit
68. CUI Character User Interface
69. CVT Constraint Voltage Transformer
70. DAC Digital To Analog Converter
71. DBA Data Base Administrator
72. DBMS Data Base Management System
73. DDL Data Descript n Language
74. DDRAM Dynamic Densities Random Access Memory
75. DDRRAM Dynamic Densities Routine Access Memory
76. DEC Digital Equipment Corporation
77. DEM Data Management System
78. DIMM Double Inline Memory Module
79. DML Data manipulation Language
80. DMP Dot Matrix Printer
81. DNS Domain Name Server
82. DOI Dots Pen Inch
83. DRAM Dynamic Random Access Memory
84. DSP Digital Signal Processing
85. DTP Desk –Top Publishing
86. DVD Digital Video Interface
87. EAN European Article Number
88. EBCDIC Extended Binary Coder Decimal Interchange Code
89. EDI Electronic Data Interchange
90. EDSAC Electronic Delay Storage Automatic Calculator
91. EDVAC Electronic Discrete Vary Able Automatic Computer
92. EFT Electronic Funds Transfer
93. EGA Enhanced Graphics Adaptor
94. EL Electro Luminescent
95. EM Electronic Mail
96. EMACS Extended Industry Standard Architecture
97. EMAIL Electronic Mail
98. ENIAC Electronic Numerical Integrator And Calculator
99. EOF End Of File
100. EOT End Of Transmission
101. ERP Enterprise Requirements Planning
102. FAQ Frequently Asked Question
103. FDC Floppy Disk Controller
104. FDDI Fiber Distributed Data Interchange
105. FGL Fourth Generation Language
106. FORTRAN Formula Translation
107. FTP File Transfer Protocol
108. GB Gigabyte
109. GIF Graphical Interchange Format
110. GIGO Garbage In Garbage Out
111. GNU Guns Not Unix
112. GPC General Purpose Computer
113. GPIB General Purpose Interface Bus
114. GPSS General Purpose Systems Simulator
115. GPSS Global Positioning System
116. GSM Global System for Mobile
117. GUS Graphical User Interface
118. HDML Hyper Device Markup Language
119. HLL High Level Language
120. HSP High Speed Printer
121. HTML Hyper Text Markup Language
122. HTTP Hyper Text Transfer Protocol
123. I/O Input/Output
124. IBM International Business Machines
125. IBM-PC IBM Personal Computer
126. IC Integrated Circuits
127. ID User Identification
128. IETF International Engineering Task Force
129. IOD Input/output Device
130. IOR Instruction Register
131. IP Information Provider
132. IP Internet Protocol
133. ISA Industry Standard Architecture
134. ISDN Integrated Service Digital Network
135. ISO International Standards Organization
136. ISP Internet Service Provider
137. ISR Information Storage and Retrieval
138. IU Input Unite
139. JANET Joint Academic Network
140. JCL Joy Control Language
141. JPEG Joint Photography Experts Group
142. K Kilo
143. KB Kilo Byte(1024)
144. LAN Local Area Network
145. LASER Light Amplification by the Stimulated Emission of
Rendition
146. LCD Liquid Crystal Display
147. LCS Liquid Crystals Shutter
148. LDAP Lightweight Directory Access Protocol
149. LED Light Emitting Diode
150. LIFO Last In First Out
151. LISP List Processing Language
152. LISP List Processor
153. LPM Line per Minute
154. LPS Line per Second
155. LPS Line per Minute
156. LQP Letter Quality Printer
157. LSB Least Significant Bit
158. LSD Least Significant Digit
159. LST Large Scale Integration
160. MAE Metropolitan Area Ethernet
161. MAP Manufacturing Automation Portal
162. MAR Memory Address Register
163. MB Megabyte
164. MBR Memory Buffer Register
165. MDAS Medicate Data Acquisition System
166. MF Master File
167. MIDI Musical Instrument Digital Interface
168. MIME Multipurpose Internet Mailing Extensions
169. MIPS Million Instruction Per Second
170. MIS Management Information System
171. ML Marching Processing Language
172. MODEM Modulator Demodulator
173. MOO Mud Object Oriented
174. MOS Metal Oxide Semi Conductors
175. MPEG Moving Pictures Experts Group
176. MR Memory Register
177. MR Modem Ready
178. MSB Most Significant Bit
179. MSD Most Significant Digit
180. MS-DOS Micro Soft Disk Operating System
181. MSI Medium Scale Integration
182. MSN Micro Soft Network
183. MT Magnetic Tape
184. NLQ Near Letter Quality
185. NMF New Master File
186. NREN National Research And Education Network
187. NSFNET National Science Foundation Network
188. NTFS Non Transfer File System
189. OCR Optical Character Reader /Recognition
190. OH Off Hook
191. OLE Object Linking Embedding
192. OLTP Online Transaction Processing
193. OMF Old Master File
194. OMR Optical Mark Recognition Reading
195. OPCODE Operation Code
196. OPP Object Oriented Programming
197. OS/2 Operating System/2
198. PBX Private Branch Exchanges
199. PC Program Counter (Also Personal Computer)
200. PIO Processor Input/Output
201. PL Programming Language
202. POS Point-Of Sale
203. PPM Page Per Minute
204. PPP Point-To Point Protocol
205. PROM Programmable Read Only Memory
206. PSM Personal Identification No
207. PSTN Public Switch Telephone Network
208. RAMAC Random Access Method for Accounting and Control
209. RD Receive Data
210. RF Radio-Frequency
211. RGB Red Green Blue
212. RISC Reduced Instruction –Set Computer
213. RJE Remote Job Entry
214. ROMBIOUS Read Only Memory Basic Input Output System
215. RPG Report Program Generator
216. RS-232 Regular Standard No 232
217. SAGE Semi Automatic Ground Environment
218. SDRAM Single Dynamic Random Access Memory
219. SGML Standard Generalized Markup Language
220. SIMM Single Inline Memory Module
221. SLIP Serial Line Internet Protocol
222. SLT Solid Logic Technology
223. SNOBOL String Oriented Symbolic Language
224. SOH Start of Heading
225. SRAM Single Random Access Memory
226. S-SEED Symmetric Self-Electro-Optic-Effect-Devices
227. SSL Secure Sockets Layer
228. SVGA Super Video Graphic Adaptor
229. TCP Transmission Control Protocol
230. TD Transmitted Data
231. TELEX Teleprinter Exchange
232. TP Transaction Processing
233. TRADIC Transistorized Airborne Digital Computer
234. UIS Universal Information Server
235. UNIVAC Universal Automatic Computer
236. UPC Universal Product Code
237. UPS Uninterrupted Power Supply
238. URL Uniform Resource Locater
239. USB Universal Serial Bus
240. UT User Terminal
241. VCD Visual Display Unit
242. VDU Visual Display Unit
243. VGA Video Graphic Adaptor
244. VM Virtual Memory
245. VRS Voice Recognize System
246. VS Virtual Storage
247. WAN Wide-Area Network
248. WORM Write Once Read Many
249. WP Word Processing
250. WWW World Wide Web