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CONTENTS
UNIT - 1 COMPUTER CONCEPTS1.0Introduction
1.1 Objectives
1.2 Need for Computer Literacy
1.3 Computer Capabilities
1.4 Computer Concepts
1.5 A Typical PC Characteristics
1.6 Question/ Answer Key
UNIT 2 COMPUTER SYSTEM ORGANIZATION
2.0 Introduction
2.1 The System Concept
2.2 Organization of Computer System
2.2.1 Input Devices
2.2.2 Central Processing Unit (CPU)
2.2.3 Output Devices
2.3 Computer Limitation
2.4 Classification of Computers
2.5 Question/ Answer Key
UNIT 3 SOFTWARE
3.0 Introduction
3.1 Software.
3.1.1 System Software
3.1.2 Application Software
3.2 Machine Language
3.3 Assembly Language
3.4 High Level Language
3.5 Question/ Answer Key
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Chapter 1
COURSE INTRODUCTIONComputers are used in many application, like banking, military, medical instruments.
In this course we are going to discuss the fundamental concept of computers, its working,
how computer are useful for a society and its capability. How computers are classified,
what is the relationship between software and hardware and what is the use of storage
device and their capabilities are discussed.
Peripheral devices are responsible for carrying out input and output operations. The
input devices include keyboard, mouse, light pen etc.. The output devices are printers,
plotters and the monitors to name a few. Computer is an information process device,
Hence devices for storing information are needed. Main memory holds programs and
data. Main memory is volatile and limited in size. Secondary storage devices are non-
volatile and have sizes which are orders of magnitude more than the size of the main
memory. Example of secondary storage are hard disk, floppy disk, CD ROM computers
store information in the digital form. In order to make a computer communicate with the
analog world, a device called MODEM( Modulator Demodulator ) is used. Modem
converts the digital information to analog information for messages going out of acomputer and vice-versa for incoming messages. Different computers might be
equipped with different resources. For example a computer might have a printer attached
and another. Computer might have useful programs. Sharing of resource will logically
see that every computer will be able to use all the resources ( whether available locally or
not). Resource sharing becomes possible of the computer are connected together. LAN (
Local Area Network ) provide for resource sharing.
In a network of computers programs are distributed on the different computers. A
computer may have a program providing a certain service ( say printing ) running on it.
It is useful to make the service available for requests coming from else where.
Client/Server technology provides for service to be extended to request client request
origination from any point of the network.
Multimedia technology add multimedia capabilities ( audio, video) to a computer.
A multimedia kit normally has a sound card, CD-ROM or DVD Drive and speakers.
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UNIT - 1 COMPUTER CONCEPTS
STRUCTURE
1.0Introduction1.1 Objectives1.2 Need for Computer Literacy
1.3 Computer Capabilities
1.4 Computer Concepts
1.5 A Typical PC Characteristics1.6 Question/ Answer Key
1.0 INTRODUCTION
No other technology has made such a rapid growth and change in science and
technology in a short duration of time as the computer technology. Computers have a
become a part and parcel of every human beings life. One can imagine the power and
position of computers by looking into the statements " By the year 2099, there will be no
clear distinction between humans and machines, we will have merged". Within the next
20 years, computers will be powerful like our human brain.
Though computers by themselves have no intelligence and do not have the ability to
learn, they have created situations that make us feel as if computers are better than human
beings. In some ways, computers are fast, store large volumes of data and are more
efficient than human beings. Computers are largely self-directing i.e. they have the
ability to follow the set of instructions given to them ( of course, by human
beings!)without human interaction.
With limited intelligence, limited language capability (understands only
programming languages) computers continue to dominate in the field of science and
technology.
The computers have emerged as a result of countless ideas inventions and
developments made by different people throughout this century.
1.1 OBJECTIVES
After studying this unit you should be able understand computer capabilities,
functional blocks of a computer the difference between data and information, speed and
accuracy capabilities. How data is manipulated.
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1.2 NEED FOR COMPUTER LITERACY
A few decades ago, a few computers in existence were very huge and expensive,
they were usually used for scientific purposes and thus had little impact on the lives of
common people; only a few people had the knowledge of computer capabilities and
limitations.
But over the period the scenario has changed. Millions of computers ranging from
small micro-sized units to super-computers are found in offices, factories, schools,
homes, hospitals, banks, retail stores and almost every where.
Let us take a few examples and look at the use of computers
a) Travel arrangements for a trip:
An efficient computer controlled airline reservations system keeps track of
available seats and quickly records the reservation.
b) You went to a hospital for physical checkup:
If the exam is for insurance purposes, your medical history and the doctors
finding will be forwarded to the insurance company where they are stored in a
large computer data bank.
c) Visit to a supermarket:
When you go to a supermarket you can find several computers, which read the
codes (like bar code) on the products and prepares the cash bills within a few
minutes. There is no need for the customer to wait for a long time to get his
bill.
By looking at the typical sample examples listed above, the presence of computers in
your daily life cannot be ignored or under estimated.
Computers can have both good and bad effects on the individuals.
Computer applications will expand greatly in the years to come. There will be vast
potential for widespread benefits as well as undesirable side effects. Educated citizensshould not rely solely on computer specialists to prevent the possible dangers and bring
about the positive potential. Rather, citizens should learn about computers so that they
can reap the benefits and they can insist the designers of ill-conceived computer systems
to assume the responsibility for effects these systems have on people.
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The following are the areas of knowledge required for computer literacy:
1. Computers themselves: You should understand the organization,
capabilities and limitations of the various machines or hardware that make
up a modern computer system.
2. What computers do: You should be familiar with some of the most
common applications of computers in today's society.
3. How computers are put to work: You need to know the analysis, design
and program preparation procedures that must be carried out in order to
produce software. Basic knowledge of hardware is also very essential.
4. The social impact of computers at work: Finally you should know how
individuals and organizations may be affected by present and future
computer applications.
1.3 COMPUTER CAPABILITIES
Most people are aware that a computer is a machine that can perform arithmetic
operations, but it is much more than just an arithmetic number crunching device. It is
also a machine that can choose, copy, move compare and perform various non-arithmetic
operations on many alphabetic, numeric and other symbols that humans use to represent
things. The computer manipulates these symbols in the desired way through a sequence
of instructions, called a program.
A program is a detailed set of human instructions that directs the computer to
function in a specific way to produce a desired result. Electrical or electromechanical
components are known as hardware.
a. Speed and accu racy capabil i t ies:
A computer works one step at a time. It can add, subtract, compare digits and,
letters, move and copy numbers and letters. There's nothing profound in these
operations. What's significant is the computer speed. This speed is measured asmilliseconds, microseconds, nanoseconds and pico seconds (Recent study says computer
speed is being doubled every six months).
The speed required for computers to execute a basic operation like addition varies
from a few microseconds for the smallest machines to 80 nano seconds or less for the
larger ones.
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Thus, the slowest computers can perform hundreds of thousands of additions in a
second while the largest systems can compute several million additions in the same
period.
In addition to being very fast, computers are also very accurate. It is estimated that
you or I would make one error in every 500 to 1,000 operations with a calculator. But the
circuits in a computer require no human interaction between processing operations and
have no mechanical parts to wear out and malfunction. Thus these circuits can perform
hundreds of thousands (or millions) or operations every second and can run errorless for
hours and days together at a time.
Beyond this, computers also have built-in self-checking capabilities that permit them
to monitor the accuracy of their internal operations.
If the input data are correct and relevant, and if the program of processing the
instructions is reliable, then the computer can generally be expected to produce accurate
output. The phrase " Garbage in, Garbage-out" or GIGO is used often by people who
work with computers to illustrate the importance of input data and correct instruction.
b. Data manipulat ing c apabi l ity :
The first computers were built to manipulate numbers in order to solve arithmetic
problems. Along with numbers we also use alphabets and different symbols in our daily
life. Luckily, early computer experts made the important discovery that a machine that
can accept, store and process numbers can also manipulate non-numeric symbols.
Manipulating these familiar symbols is possible if an identifying code number is assigned
to the symbol to be stored and processed. Thus, the letter A can be represented by a
code, as can the letter B, the addition symbol and so on. Of course, one must give the
computer instructions for it to manipulate the coded and stored symbols in a desired way.
c. Data - versu s - inform ation:
The word " data" is the plural of datum, which means fact. Data then, are facts or
raw material of information. Data are represented by symbols.
Information is data arranged in ordered or useful form. That is information is
relevant knowledge produced as output of data processing operations and acquired by
people to enhance understanding and to achieve specific goals.
The following schematic representation shows you the processing of raw data to
provide information:
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Data Raw data Data Information End user
decisionsCollection input processing output and
actions
d. Data Process ing activi t ies:
Data processing consists of gathering the raw data input, evaluating and bringing
order to it and placing it in proper perspective so that useful information is produced. All
data processing, whether done by hand or computer system consists or three basic
activities: capturing the input data, manipulating the data and managing the output
results.
i) Capturing the input data:
Data must be originated in some form and verified for accuracy prior to further
processing. They may initially be recorded on paper source documents and then
converted into a machine - usable form processing or they may be captured directly in
paperless machine-readable form.
ii) Manipulating the data:
One or more of the following operation may have to be performed on the data that is
collected.1. Classifying:Organizing items with like characteristics into groups or classes is
called classifying. Data taken from a materiel stores sales bill for example, may
be classified by product sold, Sales department sales person, or any other
classification useful for store management. Classifying is usually accomplished
by assigning pre-determined abbreviation codes to the items being arranged. The
three types of codes used are numeric, alphabetic and alphanumeric.
2. Sorting: Usually its easier to work with data if they are arranged in a logical
sequence. For example: include first to last, biggest to smallest oldest to newest.
Arranging classified data in such a sequence is called sorting.
3. Calculating: Arithmetic manipulations of the data is called calculating. For
example: In calculating a sales person's pay, the hours worked multiplied by the
hourly wage rate gives the total earnings. Payroll deductions such as taxes are
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then calculated and subtracted from total earnings to arrive at the sales person's
take-home pay.
4. Summarizing: Reducing masses of data to a more concise and usable form is
called summarizing.
Example: the general manager of a retail store is interested only in a summary of
the total sales of each department. A summary report would give only total sales
information. Department managers may want more detailed information such as
the total sales of each department broken down into sales by product type and by
sales person.
e. Managing the outp ut resul ts:
Once the data have been captured and manipulated, one or more operations may beneeded.
i) Storing and retrieving: Retaining data for future reference in storing,
storage media such as paper ( in sheet, punched card or punched tape
form), microfilm, or magnatic disks and tapes are generally used.
Recovering stored data and / or information is the retrieving activity. One
slow approach is for people to search file cabinets. A much faster method
is to use electronic enquiry devices that are connected directly to a
computer and mass storage unit containing the data.
ii) Communicating and reproducing: Transferring data from one location
or operation to another for use or for further processing is data
communication a process that continues until information in a usable
form, reaches the final user. Some times of course, its necessary to copy
or duplicate data. This reproduction activity may be done by hand or by
machine.
1.4 COMPUTER CONCEPTS
There's nothing new about the data processing steps just stated above. They have
been performed down through the ages, first by hand, then by machine assisted manual
and electromechanical punched card methods and now by computers.
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The four functions which follow are all that a computer can perform but they also
include most data processing steps:
i) Input / Output operation:A computer can accept data(input) from and
supply processed data(output) to a wide range of input/ output devices.
Such devices as keyboards and display screens make human - machine
communication possible. Multiple output documents may be reproduced
by printers.
ii) Calculation operations:The circuits in a computer are designed to permit
addition, subtraction, multiplication and division.
iii) Logic/ Comparison operation: The computer also has the ability to
perform certain logic operations. For example, when two numbers
represented by the symbols A and B are compared, there are only 3
possible outcomes:
1) A is equal to B ( A=B);
2) A is greater than B (A>B) or
3) A is less than B (A
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This comparison ability makes it possible to classify item A is having or
not having the characteristic of B. This simple ability to compare is an
important computer property because more sophisticated questions can be
answered by using combinations of comparison decisions.
iv) Storage and retrieval operations: Both data and program instructions
are stored internally in a computer. Storing both data and instructions in
same memory is known as stored program concept or John Von
Neumann Concept. And once stored, both may be quickly called or
retrieved for use. The time required for data to be retrieved is measured
in micro-or nanoseconds.
1.6 TYPICAL PC CHARACTERISTICS
Some of the major characteristics of a typical personal computer are summarised
below. This should give a glimpse of a desktop computer and introduce you to some of
the terms used with personal computer.
FEATURE TYPICAL BRIEF DESCRIPTION
CPU type 8088, 80286, 80386, 80486,Pentium-I, II, III
The CPU determines howmuch memory the system
can address, what kind of
software it can run, and
how fast it can go
Bus type PC Bus (8-bit ISA), AT Bus(16-bit ISA), Proprietary
32-bit Micro Channel,EISA, Local or VESA bus,
PC-Card, PCI
The bus determines whatkind expansion circuit
boards will work in themachine. Most buses are
incompatible with theothers (exception: EISA
bus computers can use ISA
cards), which makes itimportant that you know
which kinds of boards
youre buying
BIOSmanufacturer
American Megatrends, Inc(AMI), IBM, Compaq,
Phoneix, Award
BIOS (Basic Input/OutputSystem) is the low-level
system software that
determines how
compatible your computeris.
CPU Speed 4.77 MHz (PC speed) upto
200 MHz
Megahertz (MHz) is a
rough measure of system
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speed. All other thingsbeing equal, a 10 MHz
machine is faster than a 5
MHz machine. (All other
things generally arent
equal)Video board Monochrome Adapter
(MDA), Color/Graphics
Adapter (CGA), EnhancedGraphics Adapter (EGA),
Video Graphics Array
(VGA) 8514 Adapter,
Extended Graphics Array(XGA), Diamond Viper
ATI Mach 32.
The video board affects
what kind of software you
can run and how quicklydata can get on the screen.
It can be easily changed,
and the oldest PC can use
anything from amonochrome board up to a
VGA or 8514. Changing
video boards may require
updating software to usethose video boards. Video
boards vary by the numberof colors and pixels (the
dots on the screen) that
they can display. Most
important in modern videoboards, however, is
whether they hold video
data as a simple Dumb
frame buffer which
requires that the CPU mustdo all the video work, or
contain circuitry that canhelp with the grunt work
of graphical screens:
boards like that are said to
be bitblitter boards.
Parallel port Unidirectional, Bi-directional, EPP (Enhanced
Parallel Port)
The parallel port acts asthe basic interface for
printers. In its simplest
form, its unidirectional.
More modern parallelports may support bi-
directional data flow, ormay even support higher
speeds of data
transportation, known as
an Enhanced Parallel Port,usually abbreviated EPP.
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Bi-directional parallelports are more and more
essential in order to
support newer printers,which work their best
when teamed with a bi-directional or, better, EPP
port.
Serial port UART 8250, 16450, 16550 The UART is the mainchip around which a serial
port or internal modem is
built. The 16550 UART is
the fastest of the lot, and isessential for high speed
communications and
communications in
multitasking environments.Amount of
memory
640K - whatever There are several kinds of
memory or RAM (Random
Access Memory)conventional, extended,
and expanded. They all
solve different problems.
Some software wont runwithout a particular
amount of one or more ofthese kinds of memory.
Most PCs come with 64 or128 MB of RAM.
System Clock /Calendar
Built on motherboard oradded on expansion board.
Again, not terriblyimportant. Machines with
built in clocks usually have
DIS support to directly
read from or modify thetime and date. Others
must run a separate
program.
Hard diskinterface ST506/412, ESDI, SCSI,IDE, EIDE What method does thehard disk controller (acircuit card in the system)
use to talk to the hard
disk? This affects speedand can be easily changed
in most systems. Modern
systems use IDE or SCSI;
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SCSI is preferable for itsflexibility.
Hard disk
encoding scheme
MFM, RLL, ARLL How much data is
squeezed on to the area on
disk called a track? These
methods are used tosqueeze more data onto a
hard disk, and can easily
be changed.
Keyboard type XT-type, AT-type IBM originally put a
keyboard control chip in
the keyboard for the PC
and XT. They moved it tothe motherboard for the
AT, so youve got to know
which kind of keyboard
interface youve got. Mostclone keyboards have a
switch allowing them to
swing both ways.
Floppies
supported
5.25 inch 360 K, 1.2MB,
720K (Unusual); 3.5inch
720K, 1.44 MB, 2.88MB
What kind of floppies will
your machine support?
This can be changed fairly
easily.
Number ofexpansion slots
3-10 The more, the merrier.Many bit-name computers
only sport three expansionslots; look instead for theeight-slot models.
Configuration
method
Switches configuration
(CMOS) memory
Computers wont work
until you tell them about
themselves, or configure
them. Its done with eitherphysical switches or
software.
Number of
interrupts (IRQ
levels) supported
8 or 16 Affects the number and
type of expansion boards
in a system.Number of DMA
(Direct Memory
Access) channels
supported
4 or 8 Affects the number and
type of expansion boards
in a system.
Sound Card 8 or 16 bit FM, MIDI,and/or wavetable Audio
interface
Sound boards supportmusic and sound
reproduction on your PC,
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but music and sound arerepresented in either an 8-
bit or a 16-bit format. 16-
bit is better, but takes morespace. The sounds are
recorded and reproducedeither with FM synthesis,
MIDI control, orwavetables. Additionally,
a sound card in
combination with a CD-
ROM can play music onyour PC, with the right
audio interface cable.
SCSI host
adapter
SCSI-I or SCSI-II single
ended or differential;
normal, fast, wide, orfast/wide
SCSI is a kind of universal
hardware interface that
allows you to put harddisks, CD-ROMs, tape
drives, optical drives, andscanners onto your
machine with a minimum
of hookup trouble. SCSI is
still an evolving standard,but with many choices
Most PCs dont have
SCSI, but most couldbenefit from adding SCSI;
all you need is the SCSIhost adapter board and
some software.
LAN board Ethernet, Token Ring andARCNet
Local area networks(LANs) allow PCs to
communicate with one
another, share data and
printers. Each PC on aLAN needs a LAN
transceiver card, and there
are three types: Ethernet,
Token Ring, and ARCNet.Ethernet is the most
common. Most businesseshave LANs, and more and
more homes are adding
LANs as they acquire PCs.
CD-ROM Drive Spin speed (internal or
external) SCSI, IDE or
support CD-ROM disks,
which can hold almost 700
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proprietary interface MB of data. More andmore software ships solely
on CD-ROM, making this
item a necessity. Theyvary largely by whether
theyre internal or external,and how quickly they can
transfer data to a PC.Transfer speeds range
from 150K/s (single
spin), 300K/s (double
spin), 450 K/s (triplespin), to 600 K/s (quad
spin), 900 K/s (six
speed). 1200 K/s (eightspeed, 1500 K/s (ten
speed) CD-ROMinterface either by way ofIDE or a SCSI host adapter
or by way of a proprietary
adapter.
Printer Control
language
Epson codes, HPPCL
(Laser jet commands) PostScript others.
Printer control languages
tell your printer how tounderline words, put
pictures on the page, and
change typefaces.
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1.6 QUESTION/ ANSWER KEY
1.A _____________________ is a fast and accurate electronic ( or data)
manipulating system that will accept and store input data, process them and
produce output results.
2._________________________ are facts or informational raw materials
represented by symbols
3.Arranging classified data in a predetermined sequence to facilitate processing is
called ______________________.
4.The word " data" is the plural of datum which means __________________.
Answers:1. Computer 2. Data 3. Sorting 4. Fact
Mark True or False
True False
1. Electrical or electromechanical components are known as hardware.
2. A Program is considered as hardware
3. Keyboard is considered as output device
Answers:
1. True 2. False 3. False
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Chapter 2
COMPUTER SYSTEMORGANIZATION
STRUCTURE
2.0 Introduction
2.1 The System Concept
2.2 Organization of Computer System
2.2.1 Input Devices
2.2.2 Central Processing Unit (CPU)
2.2.3 Output Devices
2.3 Computer Limitation
1.1Classification of Computers
1.2Question/ Answer Key
2.0 INTRODUCTION
Lets take a look at our computer definition. A computer is a fast and accurate
symbol manipulating system that is organized to accept, store, process and produce
results under the direction of a stored program of instructions.
This section explains the computer is a system and how a computer system is
organized. Organization of computers input devices, Keyboard, mouse and classification
of Computers.
2.1 THE SYSTEM CONCEPT
The system is a group of integrated parts that have the common purpose of achieving
same objectives. The following characteristics are important:
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1. A group of parts : A system has more than one element. A steel ball is not a
system but it might be part of a bearing assembly that could be combined with
other components to produce an irrigation system.
2. Integrated parts: A logical relationship must exist between the parts of a
system, mechanical and electronic systems such as washing machines and
video games have components that work together. And a personal
management system may consist of integrated procedures for recruiting
training and evaluating employees.
3. Common purpose of achieving objectives: The system is designed to
accomplish one or more objectives, all system elements should be controlled
so that the goal is achieved. Totally automated systems have highly
controlled operations, systems operated by people sometimes get out of
control.
A computer is a group of integrated parts that have the common purpose of
performing the operations called for in the program being executed it is also a
system. Any system may be comprised of smaller systems or subsystems.
A subsystem is a smaller system contained within a larger one. The
component parts found in most computer system ex: printers are systems in a
way and computers in small may be considered subsystems in larger
supersystems such as air traffic control system.
2.2 ORGANIZATION OF COMPUTER SYSTEM
Input central output
Devices processing unit devices
Fig. 1 Overview of Processing
The figure above shows the basic organization of computer system. The system
included input, processing and output devices. Let us see each component of the system
in more details.
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2.2.1 Inpu t Devic es
Computer systems use many devices for input purposes. Some allow direct human/
machine communication. The keyboard of a workstation connected directly to or online
to a computer: Devices that read data magnetically recorded on specially coated plastic
tapes or floppy plastic disks are popular. Regardless of the type of device used, all are
components for interpretation and communication between people and computer systems.
There are few important input devices which we will learn in details.
Keyboard: Is the most friendly input device through which data programs are keyed
in and certain commands to software can be given from the keyboard.
The keyboard consists key switches there is one key switch for each letter, symbol
number etc. much like a typewriter when a key is pressed, the key switch is activated.
The keyboard has an electronic circuit to determine which key has been pressed. Thenthe 8-bit binary code is generated and sent to the computers. The binary code may
be an ASCII ( American Standard Code for Information Interchange), EBCDIC (
Extended Binary Coded - Decimal Interchange Code) or Hex code.
Fig. 2 Key Board
Keyboards are classified into two types depending on the number of keys present in
them.
a) Ordinary Keyboard: consists of 86 keys.
b) Extended Keyboards: consists of 101 keys ( Windows ready )
Computer Keyboard
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Keyboards are of two types based on the fashion of data transfer.
a) Serial Keyboard: It sends the data, bit by bit in a serial fashion and the computer
converts the data into a parallel type.
b) Parallel Keyboard: It sends the data as a byte in parallel form, the bits are sent
simultaneously on different lines( wires).
Mouse:A mouse is a graphical input device the term mouse is used because of its
shape. The mouse has two or three buttons on its top. The function of each button is
defined by the software. The mouse also has a small rotating ball at the bottom. When
the mouse is moved on a rubber pad, the ball rolls whose movement is converted into an
electrical signal and seat to the CPU on the CPU this movement is interpreted and
displayed on the screen of the monitor (CRT) in the form of movement of the arrow mark
. This movement of arrow mark is used to highlight the graphical index on the screen.
When a desired command shown on the screen is approached by the arrow mark due to
the movement of the ball in the mouse the click button is pressed to highlight the same.
Fig. 3. Mouse
There are 2 methods by which a mouse is connected to a computer serial interface
and parallel interface.
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2.2.2 CENTRAL PROCESSING UNIT (CPU)
The heart of any computer system is the CPU. Three main sections are generally
located within computers of all sizes.
a) The Primary Storage Section: This section is used for four purposes.
1. Data are fed into an input storage area where they are held until ready
to be processed.
2. A working storage space that holds the data being processor and the
intermediate results of such processing.
3. An output storage area holds the finished results of the processing
operations until they can be released.
4. In addition to these data-related purposes, the primary storage section,
also certains program storage area that holds the processing
instructions.
In addition to primary memory storage or main memory section most
computers also have secondary storage capabilities ( like hard disk,
floppy disk )
b) The arithmeticlogic section:
All calculations are performed and all comparisons (decisions) are made in
the arithmetic logic section of the unit are temporarily placed in a designated
working storage area until needed at a later time data may thus move from
primary storage to the secondary storage many times before the processing is
finished. Once completed, the final results are released to an output storage
section and from there to an output device.
c) Control Section :
The control section maintains order and directs the operation of the entire
system. Although it does not perform any actual processing on the data, the
control unit acts as a central nervous system for the other components of the
computer. At the beginning of processing, the first program instruction is selected
and fed into the control section from the program storage area. There it is
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interpreted, and from their signals are sent to other components to execute the
necessary actions.
2.2.3 OUTPUT DEVICES
Output devices:- Like the input devices, output devices are instruments of
interpretation and communication between humans and the computer system. Printer is
Considered as output device.
All input/output and secondary storage units are sometimes called peripheral devices.
2.3 COMPUTER LIMITATIONS
Computers although they are very useful, they have some limitations.
i ) Programs mu st be rel iable:
As a machine, the computers does what it's programmed to do and nothing else.
This doesnt mean that it must be stupid clever programs can be written to direct the
computers to store the results of previous decisions. But a seemingly flawless program
that has operated without a problem for months can suddenly produce non-sense. A
reliable program thats supplied with incorrect data may also produce non-sense.
i i ) App l icat ion logic mu st be understood:
The computer can only process applications which can be expressed in a finite
number of steps leading to a previously defined goal. Each step must be specifically and
clearly define, if the steps in the problem solution cannot be precisely stated, the job
cannot be done. The computer may not be of much help to people in areas where
qualitative material or evaluation is important.
For example, The market decision may be of a qualitative nature because sales
volume data may rest on future social, political, technological and economical events.
However, the computer can let the manager know how the product will fare underassumed price, cost and sales volume condition.
i i i ) App l icat ions mu st be sui table:
Writing programs is a human task it can be time consuming and expensive. Thus,
non-recurring jobs are often not efficient areas for business data processing applications.
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Rather as a general rule its most economical to prepare business programs for large-
volume, repetitive applications such as payrolls that will be used many times.
2.4 CLASSIFICATION OF COMPUTERS
Computers are classified by the type of data they are designed to process. Data may
be obtained either as a result of counting or through the use of same measuring
instrument. Data that are obtained by counting are called discrete data, examples of
discrete data are total number of students in a classroom. Data that must be obtained
through measurement are called continuous data. For example, of continuos data are the
speed of an automobile measure by speedometer or the temperature of a patient as
measured by a thermometer.
A digitalcomputer is a counting device that operates on discrete data. It operates by
directly counting members ( or digits ) that represent numerals, letters or other special
symbols. Just as digital watches directly count off the seconds and minutes in an hour,
digital processors also count discrete values to achieve the desired output results.
In contrast to digital processors, however, there are also analog machines that do not
compute directly with numbers. They deal with variables that are measured along a
continuo scale and are recorded to some predetermined degree of accuracy. Temperature
for example may be measured to the nearest tenth of a degree on the Celsius scale,
voltage may be measured to the nearest of hundredth of a volt. A service station petrol
pump may contain analog processor.
Analog computers may be accurate to within 0.1 percent of the correct value. But
digital computers can obtain whatever degree of accuracy is required simply by
calculating additional places to the right of the decimal point. For example; A pi( ) has a
value of 3.1416. Actually the true value of pi is 3.14159.... ( this number could go on for
pages)
Desirable features of analog and digital machines are sometimes combined to create
a hybrid computing system in a hospital intensive-care unit, for example analog devices
may measure a patients heart function, temperature and other vital signs. These
measurements may then be convicted into members and supplied to a digital component
in the system.
Classification of computers based on their size, cost & configuration.
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In this category computers are classified as micro-computers, mini computers, main
frame computers, home computers and super computers.
Micro Computers:
A Micro computer is the smallest general-purpose processing system that can
execute program instructions to perform a wide variety of tasks.
The important features of micro computers are:
1. Micro computers are known as home computers, personal computers, desktop
computers and small business computers.
2. These are small, low-cost digital computer with a micro processor as its CPU,
a memory unit an input device and an output device.
3. The word length of a micro-computer lies in the range of 8-32 bits.4. CPUs are in a single chip
5. Storage capacity is small
6. Applications include general-purpose calculations, industrial control, office
automation etc.
Personal Computers (PCs):
Personal computers are micro-computers for general-purpose computations. These
are classified as PC, PC/XT, PC/AT and super AT (or super micro) based on their cost
and configuration. All these types contain a CPU,RAM,ROM,CRT display, Keyboard
and secondary memory.
Features:
1. PC is the simplest and cheapest type of computer and it uses an INTEL 8088 (
micro processor chip) as CPU, 640 KB, RAM, 8KB ROM ( ROM can be
extended upto 64 KB) and floppy disk as secondary memory; processing
speed of a PC lies in the range 1-5 MIPS ( micro-instructions per second )2. PC/XT ( Personal computer extended technology) contains hard disk, floppy
disk drives ( 360/1.2 MB), Intel 8088 CPU, 640 KB RAM and 8 KB ROM.
This is costlier than a PC because of the hard disk it contains. PC/XT is a
single user system. Processing speed of a PC lies in the range 1-5 MIPS and
hard disk capacity lies in the range 20-80 MB.
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3. PC/AT ( Personal computer advanced technology) contains. Intel 80286 as
CPU, 640 KB RAM (expandable to 4 MB), 64 KB ROM (expandable to 128
KB), hard disk drive and floppy disk drive (360 KB/1.2 MB), its CPU is
powerful than the CPU of PC/XT and four to five terminals can be connected
to it to make it multiuser. Processing speed of PC/AT lies in the range 1-5
MIPS and hard disk capacity lies in the range 20-80 MB.
4. Super AT( or super micros) uses a 32-bit CPU, Intel 80386 & 80486. The
RAM capacity of super macros lies in the range 2-8 MB in 80386 CPU can be
extended upto 32 MB and in case of 80486 upto 64 MB. The hard disk
capacity of super macro lies in the range 200 800 MB. The processor speed
of 80386 CPU lies in the range 3-5 MIPS and that of 80486 CPU is 12 MIPS
to 25 MHz clock UNIX is used as operating system.
The processing speed of home computers and microcomputers for industrial
control is less than 1 MIPS. Home computers are used for entertainment,
basic education and home management and income tax calculation,
investment analysis etc..
Mini Computers:
The salient features are:-
1. The word length is 32 bits and their processing speed lies in the range 10-30
MIPS.
2. RAM capacity lies in the range 8 MB 96 MB ( in same it can be extended
upto 128-256 MB)
3. The hard disk capacity lies in the range 380 MB2GB ( gig bytes)
4. Most mini-computers use Motorola 68030 and 68040 CPU.
The Minicomputers which are faster and more powerful than microcomputers can
support upped 64 or even 100 terminals and some minicomputers are Uni. Processor and
some others are multi processor systems. These are used for payroll preparation and
scientific computation, multi-user and interactive applications in college universities
research organizations, industries, sophisticated real time(industrial) control, interactive
engineering design work etc..
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Examples of mini computers are:
IBMAS/400/B60
VAX8842(VAX stands for Virtual address)
Extension - VAX computers are manufactured by Digital Data
Corporation)
WIPRO S68030V & S-6833V built around 68030 CPU
WIPRO LANDMARK 860 ( a super mini) built around Intel i860-
CPU
HP 9000 series 800 ( super mini) built around Hewlett Pacards
VLSI RISC processors
HCL magnum built around 68030 CPU and 68040 CPU.
4. Main-frame Computers:-
The mainframe computers are faster and more powerful than mini computers. These
computers are used where large amount of data are to be processed or very complex
calculations are to be made and these tasks are beyond the computing capacity of mini
computers.
The main features are :
The word length may be 48, 60 or 64 bits.
Memory capacity range is 64-256 MB and hard disk capacity is
1000 MB10 GB or more.
Processing speed lies in the range 30-100 MIPS.
The mainframe computers are used in research organizations, large industries,
business organizations, government organizations, banks and airline reservations etc..
Example: IBM 4300 series
IBM 308X series
Latest model IBM 3090 series
IBM 9000 series
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HP 9000 series 8705/400
HP 9000 model 8705/300
5. Supercomputers:
The salient features are :
1. Their word length is 64-96 bits; memory capacity is 256 MB & more; hard
disk capacity 1000 MB and more
2. Processing speed lies in the range of 400 MIPS 10000 MIPS. In a single
machine cycle tow 64bit data can be added
Super computers are much faster and more powerful than mainframe computers.
Super computers are specially designed to maximize the number of FLOPS ( FloatingPoint Operations Per Second). Their FLOPS rating is usually more than igiga flops per
second. A super computer contains a number of CPUs which operate in parallel and
make it faster. They are used for massive data processing & solving very sophisticated
problems.
They are used for weather forecasting weapons research and development, rocket
launching, seismology, atomic, nuclear and plasnia physics.
Example:-
CRAYXMP/14, X-MP/24 & X-MP/48
CRAYMP, CRAYZ, CRAY3, CRAY Y-MPC
ETA 10 ( Developed by control data Corporation )
SX2 (Developed by Nippon Electric Corporation, Japan)
SX3R ( 25.6 GIGA FLOPS )
HITACS300 ( 32 GIGA FLOPS, HITACHI MAKE )
2.5 QUESTION / ANSWER KEYS
True False
1. Digital Computer Operates on continuous data
2. Random access memory is secondary storage memory
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3. Classification of computers done depending on size, cost and
Configuration.
4. CRAY XMP/14 is a minicomputer
Answers :
1. False 2. False 3. True 4. False
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Chapter 3
SOFTWARESTRUCTURE
3.0Introduction
3.1Software
3.1.1 System Software
3.1.2 Application Software
3.2Machine Language3.3Assembly Language
3.4High Level Language
3.5Question/ Answer Key
3.0 INTRODUCTION
Software is a set of instructions to perform a task. Hardware is an electrical or
electromechanical components of a computer. Software and hardware plays an important
role for a computer. This unit discusses software and types of languages used on a
computer.
3.1 SOFTWARE
Software is defined as a set of programs that activate the hardware of the computer.
A program is nothing but as sequence of instructions where each instruction is a
command given to the computer to perform a certain specified operation or given data.
Software can be classified into two parts:
1. System Software
2. Application Software
3.1.1 System Softw are
It is a collections of programs executed as needed to perform functions such as:
i) Receiving and interpreting user commands.
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ii) Entering and editing applications programs and storing them as files in
secondary storage.
iii) Controlling I/O units to receive input information and produce output
results.
iv) Translating programs from source from entered by the user into object
from consisting of machine instructions.
v) Linking and running user written applications programs with
standard routines that exist on the system.
The system software consists of operating system, assembler, compiler, interpreter,
debugging programs, text editors etc..
3.1.2 Ap plication Softw are
An application software is the software that has been written to processor perform a
specific job.
Example: Word processing packages for processing and manipulating text,
spreadsheet packages for calculating finances and data analysis, CAD for designing and
drafting etc..
3.2 MACHINE LANGUAGE
A computer understands information composed of only zeros and ones hence it uses
binary digits for its operation. A program written in the form of 0s and 1s is called
machine language program. There is a specific binary code for each instruction. For eg:
to add the contents of register A and register B, the binary code is 10000000 for Intel
8085 microprocessors. The binary code for certain operations differs from computer to
computer.
3.3 ASSEMBLY LANGUAGE
Writing programs in machine language is very difficult, tiresome and boring job for
a programmer, it is error phone. To solve this problem and to facilitate programmer
easily understandable languages have been developed. Assembly language is one of
them. Programs can easily be written in alphanumeric symbols instead of Zeros & Ones
meaningful and easily remarkable symbols are selected for this purpose.
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Example: ADD, for addition, SUB for subtraction CMP for comparison.
Such symbols are called mnemonics. A program written in mnemonics is called
assembly language program.
Assembler
A program which translates an assembly language program into a machine language
program is called an assembler.
Assembly languageAssemblerMachine language
(Source Program) (Object program)
Disadvantages
1. Programming is difficult and time consuming
2. The assembly language is machine oriented i.e the programmer must have theknowledge of the hardware of the computer
3. The program written in assembly language for one computer cannot be run on
another computer
3.4 HIGH LEVEL LANGUAGES
A High level language is one which is expressed in terms of simple English like
language.
The instructions written in high level language are called statements. The statements
more clearly resembles English Mathematics as compared to mnemonics.
Example:
BASIC, PASCAL, FORTRAN, COBOL, ALGOL, LISP, ADA, SNOBOL
Advantages
1. They are easier to learn as compared to assembly languages.
2. They make programs easier and faster to write
3. Provide better documentation.
4. The programmers does not have limitations to use a single type of machine.
5. Programs are portable i.e. they will run on any computer
Many high level languages have been developed, some are for general purpose and
some for special purposes.
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Example:
PASCAL, PL/1, ADA AND C are general purpose languages.
COBOL is for business purposes
PROLOG is for logical reasoning
BASIC for new comers
SNOBOL for text processing
Source language and Object language
The language in which a programmer writes programs is called source language. It
may be high-level or assembly language. The language in which the computer works is
called object language or machine language.
Compi ler
A program which translates a high-level languages into a machine language program
is called compiler. For example, WATFOR (FORTRAN compiler ), TURBO PASCAL
compiler.
Interpreter
An interpreter is a program which translates statements of a high level language
program into machine code.
In translates one statement of the program at a time. It reads one statement of a high-
level language program translates it into machine code and executes it. Then it goes to
the next statement.
On the other hand a compiler translates the whole program into machine code-
Highlevel Compiler Machine
Language or Interpreter language
(Source (Object
Program) program)
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3.5 QUESTION/ ANSWER KEYS
State True or False:
1. Machine language is one which is expressed in terms of 0's & 1's.
2. Assembly Language is one which is expressed in terms of mnemonics
3. Compiler is a software which converts machine language to high level
Language.
4. Fortran is a low level language.
Answers :
1. True 2. True 3. False 4. False.
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Chapter 4
PRINTERSSTRUCTURE
4.0 Introduction
4.1 Objectives
4.2 Printers
4.3 Types of Printers
4.4 Check your progress
4.0. Introduction
This deals with computer hardware that are used for outputing data from a computer
and it also introduces various types of printers.
4.1. Objectives
The objectives of this unit are
To introduce computer hardware which forms the essential components
of a computer system.
Which provides hard copy of the output.
4.2 Printers
One of the most convenient and useful methods by which the computer can deliver a
hard copy is by means of printing. For the sake of convenience, the printer should have
the ability to print alphabetic character, decimal digits, and common punctuation marks
etc..
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Funct ions of a Pr inter
The printer receives data characters from the computer and prints the characters on
the paper. In addition, the printer also receives control characters from the computer.
These control characters are not printable characters. They convey some sort of control
information to the printer ( bold, italic underline etc.). Some of the control characters
widely used are:
CR(Carriage Return) : Specifies that the pointer head carriage should return to the
first print column. Any subsequent data character received will be printed starting from
the first column.
LF(Line Feed): informs the printer to skip one line on the paper.
FF (Form Feed): Instructs the printer to skip the paper to the beginning of the next
page or form. In addition to these the printer has to send acknowledging signal back tothe computer indicating the status.
Basic c haracter ist ics of a pr inter :-
1. Speed: Specified as CPS ( Character Per Second ) or LPM ( Lines Per
Minute ). It indicates how fast a printer works.
2. Quality:Specified as DRAFT, NLQ ( Near Letter Quality ) or LQP ( Letter
Quality Printer). This give how good the shape of the printer character is.
3. Character Set: Indicates the total number of data characters and control
characters recognized by the printer. The normal ASCII and EBCDIC.
4. Interface: Specifying whether the printer receiving characters from the
computer in parallel form or in serial form.
5. Buffer size:Indicates how many data characters can be stacked in the printer
buffer memory before printing.
6. Print size:Specified as character size and number of characters per line.
4.3. Types of printers
There are several types of printers that are designed for different types of
mechanisms based on the approach of printing and speed; printers may be classified as:
1. Character printers
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2. Line printers
3. Page printers
Printers are also classified as:
1. Impact printers and
2. Non-impact printers
Impact printers: The printers which use the familiar type written approach of
hammering a typeface against paper and inked ribbon are called impact printers.
Non-impact printers:The printers which do not hit or impact a ribbon to print, are
called non-impact printer such printer uses thermal, electrostatic, chemical and inkjet
technologies.
Character printers: This category of printers generally function in the same way
as a typewriter. There are many types of character printers some of them are:
Daisy-wheel printers: In daisywheel printer the raised letters are attached at the
ends of spokes of a wheel. A motor spins the wheel at a rapid rate. The wheel is rotated
until the desired letter is in position over the paper and then solenoid-driven hammer hits
the spoke against the ribbon to print the letter. The daisy-wheel printers are impact
printers. The advantages of the daisy-wheel printers are high print quality,
interchangeable fonts and print speed upto 55 characters per second. However the print
quality is not as good as that produced by the spinning golf ball.
Fig 4.1 Daisy Wheel Printer
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1. Spinning golf ball printers: This also function in the same way as a daisy-wheel
printer. The main difference in the mechanism is that the entire character set is
present as raised type around a sphere.
The bottom of the sphere is connected to the motor drive mechanism. The ball can be
easily shifted up or down, rotated and tilted until the character to be printed can be
precisely positioned over the desired location on the paper. For printing the letter on
the paper, the spinning golf ball is hit against the ribbon. The head is moved across
the paper to print a string of characters.
The advantages of spinning golf ball printers are excellent print quality and easy
interchangeability of fonts. However, this type of printers posses some disadvantages
too, i .e it is mechanically complicated and noisy mechanism. It has low speed about
14 character per second.
2. Line printers:Are most suitable for massive data with higher speed of printing:
Fig. 4.2 Line Printer
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Drum pr inters:-
A drum type printer consists of a rapidly spinning drum which has a complete raised
character set constructed around it for each character position across the paper.
Each band contains all the possible characters, Magnetically driven hammers are
provided in each character position to hit the paper and ribbon against the spinning drum
for printing the desired characters. An entire line of characters can be printed during each
rotation of the drum.
With the help of the drum printer upto 2000 lines/min can be printed. The quality of
printing is not good and there is also high noise pollution.
Drum printers are also called line printers.
Chain pr inters:
A rapidly moving chain called print chain is used in chain printers.
Each link of the print chain is a character's font. For printing a character, a print
hammer is located behind the paper. As the print chain rotates, the properly timed
hammers strike the paper and the ribbon together against the desired character set several
times on the chain, the speed of chain printers can be improved. Speed of chain printers
reaches upto 2500 characters per minute.
Dot-Matr ix Impact prin ters:
A dot-matrix printers each character as a pattern of dots. The print head comprises a
matrix of tiny needles having seven rows with nine needles in each row. The tiny needles
hammers out the characters in the form of patterns of tiny dots. The print needles are
Fig 4.3 Printing Cylinder of a Drum Printer
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arranged in a vertical column so that characters are printed out one dot column at a time
as the print head is moved across the line. The quality of the print is not so good.
However the quality of printing can be improved by printing a line twice with the dots for
the second printing offset slightly from those of the first. Print speed of dot matrix impact
printers is max of 350 cps.
Page printers:The page printers are non-impact printers having speeds over 20,000
lines per minute. The technique called Electro-photographic technique is developed from
the paper copier technology. The important type of page printers are:
1. Electromagnetic printers:
The magnetic recording technique is used in this type of printers. A
magnetic image of the matter to be printed is written on a drum surface.
The surface of the drum is then passed through magnetic powder which
adheres only to the charged areas. This powdered surface is now pressed
on to the paper to obtain the hard copy of the data. Speeds of
electromagnetic printers upto 250 characters per second may be obtained.
2. Electrostatic printers:
In such printers, a paper coated with a non-conducting electric material
which holds the charges of voltages are applied with writing heads, is
used, The heads( or nibs) write dots on the paper as it passes. The paper is
now passed through a toner which contains material with particles
carrying an opposite charge to that of that of the paper written by the nibs.
The particles adhere to the magnetized areas and form printed characters.
3. Laser and xerographic printers:
The principle of laser printers and xerographic printers, is almost the
same, The image of the page to be printed in first formed on a
photosensitive drum in the printer. Powdered ink or tones is applied to the
surface of the drum. Now, the image from the drum is electrostatically
transferred to the sheet of paper. The ink image on the paper is finally
fused by heating process internally.
In case of a laser printer, the image on the photosensitive drum is
produced by a laser beam. The laser is swept backs and forth across the
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drum to produce an image in the same way as produced on a roaster scale
CRT. The rotating mirror sweeps the laser beam across the rotating drum,
With the help of a modulator controlled by a microcomputer, the laser
beam is turned on or off to produce dots. After the image is inked and
transferred to the paper, the drum gets cleaned and gets ready for the next
page. The speeds of laser and xerographic printers are to the tune of
20,000 lines per minute. The quality of print is also good.
4.4 CHECK YOUR PROGRESS
1. Pick up the correct statements from the following:
a) Typical speeds of drum printers may be in the range of 300 to 2000 lines per
minute.
b) Typical speeds of chain printers may be in the range of 400 to 2500 characters per
minute.
c) Typical speeds of page prints may be even more than 20,000 lines per minute.
d) All the above.
2. Printers:
a) are most commonly used o/p device
b) are used to prepare permanent documents
c) are of several types
d) all the above
Fig 4.4 Laser Printer
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3. The impact printers use:
a) Thermal technology
b) Chemical technology
c) Electrical technology
d) None of the these
4. Drum printers is a:
a) Line Printers
b) Letter Quality Printers
c) Dot-Matrix Printers
d) None- of the above
5.The primarily used computer device for obtaining the hard copy is:
a) Line Printers
b) CRT
c) Keyboard
d) None
State whether the fol low ing statements are correct :
1. The daisy wheel printers are called non-impact printers
2. Line printers are impact printers
3. A printer produces a hard copy
4. Line printers print an entire line at a time
5. A Daisy wheel printer is character printer
Answers: I
1(d) 2(d) 3(d) 4(a) 5(a)
II
1)False 2) True 3) True 4) True 5) True
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Chapter 5
MEMORYSTRUCTURE
5.0 Introduction
5.1 Objectives
5.2 Types of Memory
5.3 Accessing Methods
5.4 UPS
5.5 Check Your Progress
5.0 Introduction
Memory of a computer deals with storage of information. The secondary storage
devices, which retains information in the absence of electrical power are also discuss.
5.1 Objectives
To introduce devices for storing information ( Volatile and Non-volatile )
UPS provides the back up during power failure
5.2 Types of Memory
The memory is used for storing information. It is classified into two groups
1) Primary memory and
2) Secondary memory
Primary memory: is generally termed as computers memory, the main memory.
The primary or internal storage is a most essential part of all computers. The internal
storage area is made up of several small storage areas called locations or cells. Each of
these locations can store a fined number of bits called word length of that particular
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storage unit. Each location or word has a built in and unique number assigned to it. This
number which is used to identify the location, is called the address of the location.
The primary memory actually functions when the computer operates and is
present in the computer in two different forms RAM & ROM.
Random Access Memory (RAM): The primary storage is generally referred to as
random access memory (RAM) because one can select and use any location of this
memory to directly store and retrieve data instructions. Every location of the memory is
easily accessed and time taken in each case is same.
The facility of read/write from a RAM chip entitles it to call read/write memory.
When the power is switched off, the information stored in RAM is lost.
Read Only Memory (ROM): In this memory storage information is permanently
stored. The information contained in can only be read and not written fresh informationinto it. When power is switched off the information stored inside a ROM is not erased,
ROM memories are also known as fieldstores, permanent stores or dead stores.
Cache Memory: A very high speed memory used to increase the speed of
processing is employed between CPU and main memory whose access time is close to
the processing speed of the CPU. This type of memory is called a high-speed buffer or
cache memory. However, cache memory is not addressable by the user of the computer
system.
Cache memory makes the main memory of the computer appear to be faster and
larger than what it really is. The cache memory is normally very small due to its high
cost of construction, cache memory improves the memory transfer rate and also increases
the processor space.
5.3 Accessing Methods
The memory of a computer is not actually concentrated in one place, Storage
devices are scattered throughout the machine. For instance, the operation registers are
flip flop registers which are used in the arithmetic and control units of the computer.
The storage devices are used to introduce information to the computer from the
outside world and to store results from the computer. The procedures for locating
information may be divided into two classes:
1. Random access storage devices and
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2. Sequential access storage devices.
A random access storage devices :is one in which any location in the device may
be selected at random access to the information stored in direct and approximately equal
access time is required for each location.
A sequential access storage device: is one in which the arrival at the location
desired may be preceded by sequencing through other locations, so that access time
varies according to location.
For example, If we try to read a word stored on a real of magnetic type and the piece of
tape on which the word is stored is near the center of the reel, it is necessary to sequence
through all the intervening tape before the word can be read.
Another way to subdivide storage devices is according to whether they are static or
dynamic
A static storage: is one in which the information does not change position example
flip flop, tape are of static storage devices.
A dynamic storage: Devices are devices in which the information stored is
continually changing position. Circulating register utilizing change coupled device (
CCD) delay lines are example of dynamic storage devices.
Sequentially Accessed Devices:
Punched paper tape: The paper tapes normally 1 inch (2.54 cms) wide are
available in rolls of different length. Data is coded on the paper tape in the form of
punched hole combinations, The length of the tape may be kept as required by the user.
The information is recorded as holes punched in rows across the width of the tape.
Each row represents one character. The maximum numbers of holes per row is
known as number of channels on the tape. An eight-channel tape is generally used in
computers.
A line of sprocket holes in the middle of the tape is provided for the purpose of
feeding the tape through the tape punching and reading device.
Disadvantages
i) Less numbers of characters can only be stored.
ii) The paper tape media gets easily torn.
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Advantages
i) Storage capacity of paper tape is unlimited
ii) Cost per bit stored is very low
Magnetic tape:
This is most popular storage device for large data that are sequentially accessed and
processed magnetic tape is a half-inch (1.27-cm) wide plastic ribbon, which is coated on
the side with an iron oxide material which can be magnetized. The tape ribbon is housed
in a cassette. The computer tape can be erased and reused indefinitely. The stored data
on the tape gets automatically erased as and when fresh data, is recorded in the same area
of the tape.
Recording of information: Information in binary, is recorded on the tape asinvisible magnetized and non-magnetized spots on the iron oxide side of the tape. 0 of
the binary is represented by a non-magnetized spot and 1 is represented by the
magnetized spot on the tape. The tape is divided into horizontal rows called channels or
tracks and into vertical columns called frames. Each character of the information is
recorded per frame based on the code of the computer.
Data transfer rate: The product of tape density and tape speed is known as the data
transfer rate of the magnetic tape. The number of frames per inch length of the tape is
called tape density. The tape density of a magnetic tape is expressed in characters perinch (CPI) or bytes per inch. The tape speed is measured in inches per sec. Data transfer
rate of a magnetic tape may even exceed 1 million bytes per second.
Adv antages of magnet ic storage:
1. The storage capacity of a magnetic tape is unlimited.
2. It possesses high data density
3. Its cost is much less than other data storage devices
4. Its rate of data transfer is high5. It is very easy to handle magnetic tapes
6. It is very easy to transfer information from one place to another.
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Draw-backs of magnet ic tapes:
1. As magnetic tape is a sequential access devices, the data recorded on tape can
not be addressed directly. The data item at the end of the tape will require
abnormal access time because all the characters before the data item need by
processed. This is why magnetic tape device is not found suitable in case data
is frequently required to be accessed at random.
2. It is not possible to interpret, the stored data to know the content of the
information.
3. Dust free environment is needed for magnetic tapes and the reel containers.
a) Tape Cassettes: A high quality digital cassette similar in appearance to the home
cassettes.
b) Cartridges: The large cassette which contains long strips of magnetic tape is called
cartridge. It is very convenient to mount the tape there is proper protection against
dirt and contamination.
Both cassettes and cartridges have low data transfer rate, i,e , less than 10,000
bytes/sec.
Random access devices:
Magnetic Disk: It is a thin, circular metal coated on both sides with a magnetic
material similar to a gramophone record. A number of magnetic disks mounted about
half-an-inch apart from each other on a central shaft which may rotate at speed of 2400 or
more revolutions per minute (RPM), consists a disk pack. Magnetic disk packs are the
most popular medium for direct access secondary storage.
Information is stored on both sides of the disks except the upper surface of the top
disk and lower surface of the lower disk. Each face of the disk is divided into a number
of invisible concentric circles called tracks. A set of corresponding tracks in all the
surfaces is called a cylinder. Each track is sub divided into sectors.
Information is recorded on the tracks of a disk surface in the form of minute
magnetic spots. The magnetized spot represents a 1-bit and non-magnetized spot
represents a 0-bit.
The information stored on a disk can be read a number of items and reading
operation is non-destructive. To write a new data, the previously stored data has to be
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erased. The storage capacity of a disk pack primarily depends on the number of disks it
contains. The storage capacity also depends on the track per inch of surface and the
number of bits per inch of track.
Magnetic Drum:Magnetic drum is also a direct access storage device that can be
used for both sequential and random processing. It is basically a cylinder with a
magnetizable outer surface. A motor rotates the cylinder on its axis at a rapid speed but
constant rate. The surface of the drum is divided onto a number of tracks upon which
data is stored as magnetized spots similar to that of a disk. Data is stored on the
magnetizable surface of the cylinder as minute magnetized spots arranged in binary form
in the series of parallel circular tracks. Recording of data on the rotating drum and
reading data from the drum is achieved by a set of secondary read/write heads positioned
very near to the drum surface. Writing a new data on the drum erases the previously
stored data simultaneously at that location. Data once recorded on the drum remainsintact until it is erased.
The drum rotates at a speed of few hundred to few thousand rotations per minute
and its access times is fast. Random access is possible to select any particular track of the
drum but once this track is identified, the data is recorded or retrieved sequentially. To
reduce the access time, sometime heads are divided into two sets. Heads are positioned
diametrically opposite i.e for a drum of 20 track 40 heads are provided.
As compared to magnetic disks, data transfer rates are faster. Due to limited storage
capacity, use of magnetic drum storage is on decline.
Winchester Disk: Winchester disk are also used as a storage device. In this unit,
disks are permanently housed and hermetically sealed in contamination free containers.
The disks are coated with a special lubricant which minimizes the friction between the
read/write heads and the disk surface .Computers using these sealed housings are said to
employ Winchester technology. The Winchester technology enables greater precision of
alignment, an increase in the number of tracks on the disk surface and a higher storage
density per track.
Winchester disks are fast and highly valuable and low priced compared with
conventional hard disk drives. They are available in sizes varying form 5.25 to 14 in
diameter and there capacities are 10,12 and 20 megabytes. Dual disk drive doubles the
capacity. Winchester disks are used in large computers.
Floppy Disk: A floppy disk is a circular Mylar disk coated and magnetically
sensitive film. Since the thickness of the Mylar disk is only a few thousandth of an inch
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it is named as floppy. The floppy diskette is coated with a magnetic material and enclosed
in a protective jacket. The floppy disks are used for backup of files and to transfer files
from one computer to another computer
Floppy diskettes can be classified as Single and double sided.
If only one side of the diskette is used to store information such a diskette is called as
a single sided disk. If both the side of the diskette is used to store information such a
diskette is called as a double-sided disk.
The diskette surface is logically divided into a fixed number of tracks (concentric
circles). Data can be read and written on the specified tracks and not in between the
tracks. Each track is divided into a number of sectors. The number of sectors in a track
depends on the size.
A read/write head contacts the disk through the head slot to read from or write to the
disk. It is designed such that it can move both forward and backward.
The outermost track is numbered as track 0. The subsequent tracks are numbered
sequentially. The Index hole is used as a reference point to indicate the beginning of a
track.
There is a facility to use a diskette only for reading previously stored information
and to prevent any attempt to write new information on it through the write protect notch.
If this notch is open writing on the diskette is permitted.
Manufacturers
Users label
Write Protect
Clamping hole
Index hole
Head slot
Fig 5.1 Floppy Disk
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Adv antages of f loppy d isks are:
They are very cheap compared with other storage
They greatly enhance the on-line storage capacity
They are also convenient off-line storage medium
The floppy disks generally available in market are of 3, 5 or 8-inch
diameter size.
5.4 Uninterrupted Power Supply (UPS)
An Uninterrupted Power Supply is a device that sits between a power supply (e.g. a
wall outlet) and a device (e.g. a computer) to prevent undesired features of the power
source (outages, sags, surges, bad harmonics, etc.) from the supply from adverselyaffecting the performance of the device.
A UPS traditionally can perform the following functions:
Absorb relatively small power surges.
Smooth out noisy power sources.
Continue to provide power to equipment during line sags.
Provide power for some time after a blackout has occurred.
In addition, some UPS or UPS/software combinations provide the following
functions:
Automatic shutdown of equipment during long power outages.
Monitoring and logging of the status of the power supply.
Display the Voltage/Current draw of the equipment.
Restart equipment after a long power outage.
Display the voltage currently on the line.
Provide alarms on certain error conditions.
Provide short circuit protection.
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There are two basic types of UPS in modern use. The first, known as 'Off-line',
passes through incoming mains power to the output sockets while the supply is good. It
monitors the line constantly for a major voltage drop that signifies power failure. It then
switches on it's inverter (the part that produces output alternating current from it's battery)
and supplies output power until the mains voltage has been restored and is stable for a
period of time. There is by definition a momentary power loss during switchover, but
typically of around five milliseconds, which is insignificant to most loads. According to
how much you pay for your UPS, you may get some conditioning of the mains power
that is passed through under normal conditions, and you may get a genuine sine-wave
output as opposed to the square-wave or trapezoidal wave that you will find on the
cheaper products.
The second type is known as an 'On-line' design because it's inverter is 'on-line'
permanently. In this design, all the incoming power is always converted to direct current,which both tops up the batteries and feeds the inverter. The inverter is constantly
producing fresh alternating current to supply the load. When the mains goes off, the
batteries are still holding up the incoming DC supply to the inverter, so the load continues
to be supplied with absolutely no break whatsoever. The inverter is a constant-duty
inverter, so this costs a little more. In any reputable on-line UPS, there is also a fail-safe
mechanism known as a 'Static Bypass' which on detecting failure in the inverter will
throw the load on the mercy of the mains supply, rather than letting it drop altogether.
This design inherently cleans the supply by virtue of reducing it to DC, then reconverting
it to fresh AC.
UPSs above 5KVA in size are almost universally on-line in design. It is difficult to
produce an on-line economically below around 600VA, so most UPSs below this size
are off-line.
Better UPSs of both designs will crop high incoming voltages and step-up low
incoming voltages without resorting to battery. When these are off-line units they are
called 'line-interactive' devices - they are nonetheless fundamentally off-line devices.
Almost all UPSs in their standard form will provide between five and ten minutessupply at full load. As a very rough estimate you can say that they will usually supply ten
to twenty minutes supply at half load. Some UPS have a facility for extended batteries.
Most on-line do, most off-line don't, but that's very general and you'll find both which
can support extended batteries. When considering UPS that support extra batteries, look
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for extension battery cabinets that incorporate battery chargers, otherwise you get a small
charger that can't cope properly with a vast battery bank.
At a certain point, depending on manufacturer and size, you'll find it becomes more
cost-effective to revert to a 10-minute UPS and a generator fitted with mains-failure
autostart. This then gives you an effectively unlimited run time.
5.5 CHECK YOUR PROGRESS
1. The primary storage unit has:
a) Faster access time
b) Smaller storage capacity
c) Higher cost per bit of storage
d) All the above
2. The performance of the CPU may be increased by providing a small memory known
as:
a) speed buffer
b) cache memory
c) both and b
d) neither a and b
3. The disadvantage of magnetic tape as secondary storage device is :
a) no direct access to data
b) no direct verification of data
c) dirty atmosphere affects the tape recording errors
d) all the above
4. Pick up the hard disk from the following:
a) magnetic disk
b) magnetic tape
c) punched paper tape
d) all the above
5. Pick up the incorrect statement from the following magnetic disk is advantages
compared to magnetic tape:
a) Less vulnerable to damage from dust.
b) Higher transfer rate of data
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c) Sequential processing is faster
d) None of the above
State whether the fol low ing statements are correct :
1. The amount of data that can be stored in the storage unit is called the storage
capacity.
2. The small storage areas in the storage are called location.
3. Primary storage is generally refereed to as RAM
4. The information stored inside a ROM gets lost when the power supply is switched off
5. In sequential access device, access time for all locations is same
6. Magnetic disk and magnetic drum are typical sequential access storage devices
7. Magnetic tape is the most suitable storage media for random access secondary storage
8. Floppy disks are popular external storage media used with small computers
9. Each character is represented on a column by a set of holes punched in various rows
10.Winchester disks are permanently housed in sealed, contamination-free containers.
Answers :
I 1(a) 2(c) 3(d) 4(a) 5(c)
II 1)True 2)True 3)True 4)False 5)False
6)False 7)False 8)True 9)True 10)True
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Chapter 6
NETWORKS AND MULTIMEDIASTRUCTURE
6.0Introduction
6.1Objectives
6.2Local Area Network (LAN)
6.3Multimedia
6.4Client Server Paradigm6.5Modem
6.6Check your progress
6.0 Introduction
This deals with communication between different computers .Computer networking
(connecting computers) allows for sharing of resources such as data and peripheral
devices. Several topologies of computer networks is also presented.
In a networked computer system, with programs distributed a model called
client/server model provided for a convenient way for programs to interact. The client
/server paradigm of the different servers is also examined.
Communication device that permits connection of digital data to an existing
telephone line is referred to as MODEM.
6.1 Objectives
To understand how resources (data and peripherals ) can be shared by
networking
To understand how different services can be provided through client/server
approach
To show how the digital and the analog worlds can be bridged through
MODEM
How multimedia kit adds multimedia capabilities to a compute
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6.2 LOCAL AREA NETWORK (LAN)
LAN is a group of computers and associated devices that share a common
communications line and typically show the resources of a single processor or server
within a small geographic are (for example, within an office building), Usually, the serverhas 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 many as thousands of users ( for example, in an FEEI network).
If you have two or more people that routinely need to easily share information and
resources you are a candidate to install a LAN, Although LANs add a level of
complexity to an office computer environment, the payback in productivity can make it
well worth the effort.
Simply put, a LAN allows you to share resources, Instead of attaching a printer toeach machine in your office, across a LAN you can share a single printer, Files that
everyone in the office needs to access frequently can be kept on the central disk drive,
and a backup routine can be implemented to ensure that these central files can be
retrieved in case of trouble, with the appropriate software, a single internet connection
can be shared by all machines on the LAN to gain access to email and the Web, LANs
can reduce the amount of money you spend on extra equipment and associated costs, and
can help improve the way people in your office use and share information.
Ne