ABOUT COMPUTER

COMPUTEREXIT
COMPUTER
Inputs, Stores and Executes Instructions.
Performs Mathematical and Logical Operations.
Outputs Results according to the user Requirements.
Press SPACE BAR to continue...
EXIT
DATA
Is a collection of Facts, Figures, Statistics which can be processed to produce meaningful INFORMATION.
For example :
EXIT
PROCESS
Includes
CALCULATION
DECISION MAKING
LOGIC
The sequence or flow of step to be followed to get the desired result.
EXIT
EXIT
HISTORY
In 1647, MECHANICAL CALCULATOR was invented and another in 1694.
The PUNCHED CARD was invented in 1801.
The CENSUS MACHINE was invented in 1887.
Between 1820 and 1870, the ANALYTICAL ENGINE was developed.
After this began the era of the ‘GENERATION OF COMPUTERS.’
EXIT
Also known as ADDING MACHINES.
Machine worked using TOOTHED WHEELS and could ADD and SUBSTRACT only.
EXIT
PUNCHED CARDS
Invented by a French weaver, JOSEPH MARIE JACQUARD in 1801 to control his Mechanical Looms.
A woven pattern on cloth is often produced by lowering needles of various hues as each row of cloth is woven.
With hundreds of threads involved, the process could get extremely complicated.
These Punched Cards controlled the movement of the threads by the PRESENCE and ABSENCE of Holes.
EXIT
Machine had 50,000 moving parts worked by mechanical gears.
Meant for both Arithmetic Calculations and to Store Data.
He also created DIFFERENTIAL ENGINE in 1822.
1.psd
EXIT
FIRST PROGRAMMER
A brilliant Mathematician, Lady AUGUSTA ADA LOVELACE assisted CHARLES BABBAGE in his creation.
She improved upon his ideas and invented new approaches to program design.
The Programming Language ADA is named in her honour.
She used a special number system called the BINARY NUMBER system.
Due to the above description, she is rightly known as the FIRST COMPUTER PROGRAMMER.
EXIT
Known as Automatic Sequence Controlled Calculator.
Built by a Harvard Professor, HOWARD AITKEN in 1937 with the help of his Students and Engineers.
It was known as MARK I.
Was 50 feet long, had 500 miles of wires and 1000s of relays.
Used till 1959.
EXIT
Data represented in 1(ON) and 0(OFF).
Vacuum tubes consumed large amount of electricity and produced large amounts of heat.
This led to the Second Generation of Computers.
EXIT
ENIAC
In 1946, ECKERT & MAUCHLY built the first ELECTRO-MECHANICAL computer called ENIAC (Electronic Numerical Integrator And Calculator).
It required the physical setting of thousands of switches and had less storage space.
It got heated up very fast and thus had to be shut down very often to cool it.
This computer was 100 feet long, weighed 80 Tonnes, had 70,000 Resistors, over 18,000 Vacuum Tubes and consumed electricity of 1,50,000 Watts.
Each time a program was changed, the writing had to be completely redone.
In October 1955, ENIAC was completely turned off.
It was developed on Experimental Basis.
4.psd
EXIT
EDSAC
Invented in 1949.
Started operating in1951.
EXIT
EDVAC
Electronic Discrete Variable Automation Computer.
Used Punched Cards for DATA ENTRY and was able to Store Programs.
EXIT
UNIVAC
Performed SELF-CHECKING.
It could work even for 24 hours a day and used MAGNETIC TAPES as INPUT MEDIA.
EXIT
LEO
Started running full DATA PROCESSING services in 1954.
EXIT
System speed increased than the First Generation Systems.
Example = ICT 1301 and IBM 1401.
EXIT
From 1966-1975
Used INTEGRATED CIRCUITS on CHIPS (Thin Wafers of SILICON) of TRANSISTORS (may be 100 transistors per chip).
Could handle more than one operation simultaneously.
Example = ICL 1900, IBM 360 & SYSTEM 4.
EXIT
More circuits on a single chip were used.
This increased the amount of data that could be processed and stored in the memory chip.
Large Scale Integration (LSI) technology and Very Large Scale Integration (VLSI) technology were used.
EXIT
From 1986 and continuing.
The entire processor of the computer can be put on a single chip.
EXIT
EXIT
A LAPTOP
Is a small, slim attache case weighing around 2 to 4 kilograms.
Offers same power as a desktop machine.
Uses reduced keyboard and mouse.
Disadvantage is bulky, difficult to operate a mouse without desk.
E.g. Toshiba 5200C and Compaq’s SLT/286.
EXIT
A NOTEBOOK
Size is approximately 21 * 29.7 centimetres and weighs around 3 to 4 kilograms.
Same power as desktop machine.
E.g. Compaq’s Contura 3/20, Acer’s AnyWhere and from Zenith Computers Limited.
EXIT
Applications limited and built-in.
E.g. HP’s HP95LX comes configured with Lotus 123 spreadsheet.
EXIT
Is bulky, needs more space and not movable.
Large applications can be stored in it.
EXIT
Is a MULTIUSER and EXPENSIVE.
Storage Capacity is between 64 MB to 4 GB.
Word Length is from 64 to 128 BITS.
Eg. CRAY, CRAY-2, NEX SX-2, ROBOT, PARAM 10000.
EXIT
Several MATH and LOGIC Processors are used.
Example - Dec 1090, Cyber 170, IBM 4300 Series, IBM360/370, UNIVAC 1100/60.
EXIT
Storage capacity is from 2 to 16 MB.
Offers advantage of MAINFRAME at a lower cost.
First was PDP-8 launched in 1965.
Example - PPDP-8, PDP-II, VAX-7500, HCL-DAYSIS
EXIT
Popular due to low rate.
Single chip contains PROCESSOR, REGISTERS and CONTROL UNIT.
Speed is only 100 Kilo Instructions Per Second (KIPS).
Maximum word length is 8, 16, 32 Bits.
Example - UPTRON-S-800, INTEL Series 8080 (PC), 80286 (PC-XT), 80386/80486 (PC-AT), PENTIUM (I/II/III- Upto 850 MHz), PENTIUM MMX.
EXIT
COMPONENTS
EXIT
MECHANICAL
ELECTRICAL
ELECTRONIC PARTS of the system.
SOFTWARE is the program that instructs a computer how to process the Data and generate the required Information.
EXIT
ANALOG Computers : used for measuring PHYSICAL QUANTITIES such as Temperature, Pressure etc.
DIGITAL Computers : Calculates Figures and Manages Text.
HYBRID Computers : is the combination of ANALOG and DIGITAL computers.
EXIT
ADVANTAGES
Very Accurate.
EXIT
DISADVANTAGES
EXIT
STORAGE OF DATA
All digital computers store Numbers, Letters, and other Characters in CODED FORM.
The code used to represent characters is the BINARY CODE.
Every character is represented by a string of ‘0s’ and ‘1s’ - the only digits found in the BINARY numbering system.
Binary code is made of binary digits called BITS.
Most computers have words that consist of 8 or 16 BITS.
In larger computers the number of BITS could be 16, 32, 36 or 40.
EXIT
4 bits make a NIBBLE.
Sequence of 8 bits is called a BYTE.
8 bytes make a OCTET.
1024 bytes make a KILOBYTE (KB).
1024 KB make a MEGABYTE (MB).
1024 MB make a GIGABYTE (GB).
1024 GB make a TERABYTE (TB).
EXIT
Symbols used are 0 and 1.
As we move to the left, the value of the digit will be two times greater than its predecessor.
Can be converted to octal, decimal and hexadecimal number systems.
EXIT
Uses 7 bits per character.
Provides 128 different arrangements including upper case, special symbols like *, %, +, hyphen(-), 10 decimal digits (0 - 9) and non-printable control characters like carriage return key.
Used to represent data internally in PCs.
Besides codes for characters, codes are also defined for End Of File, End Of Page etc.
These codes are called non-printable control characters.
EXIT
PERIPHERALS
Devices used with the computer system other than the computer itself.
EXIT
A MOTHERBOARD
Is the BRAIN of the system and controls all the functions of the computer.
Every hardware is connected to it for working.
It has the Central Processing Unit (CPU) fixed on it, which controls the working.
Serial and Parallel ports for Mouse and Printer connection; Hard Disk, Floppy Drive, CD-ROM Drive; Power, Reset, LED Switches; Keyboard, Joystick etc.
EXIT
EXIT
286 = 10 MHz
586 = 66, 100 MHz
EXIT
CELERON = 233, 266, 300, 333, 350, 400, 433, 466 MHz
P-II = 233, 266, 300, 333, 350 MHz
P-III = 450, 500, 533, 550, 667, 700, 733, 766, 800, 850, 933 MHz
P-IV = 2GHz, 2.4GHz and more..
EXIT
Microphone
EXIT
KEYBOARD
Resembles a TYPEWRITER
Has three categories
ALPHANUMERIC KEYS
Contains ALPHABETS(A - Z, a - z) and FIGURES(0 - 9), OTHERS(space, dot, comma, !, @, #, $, %, ^, &, *, (, ), -, +, /, <, >, [, ], ‘, “, ~, `, {, }, |, \ )
EXIT
Special keys : Perform Specific Tasks
BACKSPACE, DELETE (DEL), INSERT (INS), SHIFT, CAPS LOCK, SCROLL LOCK, NUM LOCK, CONTROL (CRTL), ALTER (ALT), ESCAPE (ESC), RETURN (ENTER).
FUNCTION KEYS : for SHORTHAND
F1 TO F12 (F1 FUNCTION KEY IS USED AS A HELP KEY IN MOST OF THE SOFTWARES).
EXIT
MOUSE
Invented by a Scientist DUGLES C. ENGELWART in 1977 at STANFORD Research Laboratory.
Previously known as POINTING DEVICE.
2 types are Mechanical and Optical.
One, Two and Three Buttons.
Movement is measured in HUNDREDTHS of an INCH.
Function of each button is determined by the program that uses the mouse.
A three-button mouse is quite suitable for Multimedia and Internet.
EXIT
MECHANICAL
the ball that projects through the bottom surface rotates as the mouse is moved along a flat surface.
the direction of rotation is detected and relayed to the computer by the switches inside the mouse.
E.g. Microsoft, IBM and Logitech
OPTICAL
uses a light beam instead of a rotating ball to detect movement across a specially patterned mouse pad.
E.g. MSC Corp. mouse
EXIT
SCANNER
FLATBED
Can scan and store images from books without removing the page.
ROLLER-FEED
Image is passed over a roller where it is captured.
EXIT
Information accessed with minimum effort.
Screen is made sensitive to touch and exact position is detected.
Screen is lived with LED and Photo-detectors. When user’s finger approaches the screen, light beam is broken and is detected by photo-detectors.
EXIT
EXIT
MONITORS
Also known as visual display unit (VDU).
Consists of cathode ray tube (crt) which produces a beam of electrons that makes a picture on screen.
Used to display information.
Minimum pixels in
EXIT
PRINTERS
IMPACT
We can put carbon paper between the pages to print the data on other pages
NON IMPACT
It is not possible to create a carbon copy at the same time while printing the data.
EXIT
DOT MATRIX
An arrangement of tiny hammers strikes to the ribbon to produce the desired character.
Each hammer prints a small dot on the paper to form a character.
Upto 180 characters per second can be printed.
EXIT
EXIT
PLOTTERS
Output device used to create presentation, visuals, charts, graphs, tables and diagrams.
Consists of a pen mounted on an arm moved by motors along the paper up or down to make contact with the paper.
Positioning is done by the computer in the form of horizontal (x-coordinate) and vertical (y-coordinate) position.
EXIT
PLOTTERS (CONT.)
A combination of the two arm provides movement along the horizontal and vertical axis.
Pen can be moved as small as 1000th of an inch.
Plotters plot an entire drawing at a rate of several inches per second with a resolution of a few 1000ths of an inch.
EXIT
PLOTTERS (CONT.)
Is more software dependent than any other computer peripheral and needs much more instructions than printer for producing output.
To draw clear, high quality diagrams, plotter needs high quality pens with special inks with different colours.
COLOUR plotters use four or more pens.
EXIT
STORAGE DEVICES
The size of memory is limited and is thus insufficient for storing large volumes of data.
By using backing storage it is possible to store large volumes of data on a removable storage medium.
Secondary storage media do not lose their contents in the absence of power
EXIT
ZIP DRIVE
EXIT
Temporary (volatile) storage device.
EXIT
Used as a permanent data storage device.
Buffer memory same as cache memory is built within a solid state device.
Interfacing cable is a 40-pin connector.
EXIT
FLOPPY DISK
A long slit is provided for the read/write head to access the disk.
A hub in the centre is used for mounting the disk drive.
A hole is used to sense the index marking.
Inserted into the drive mechanism which rotates the flexible disk inside.
Read / Write head is in physical contact with the disk.
EXIT
whether disk is write protected
Only 1.44 and 2.88 MB floppy drives have sensors mentioned above.
EXIT
FLOPPY DISK (CONT.)
3.5” in diameter
High density have 80 tracks, with recording density of 96 tracks per inch, 18 sectors per track, 2 heads, 300 rotations per minute and data rate of 500 Kbps. Total capacity is 1.44 MB (1,457,664 bytes).
Floppy disk type is Rigid.
EXIT
Non erasable disk used for storing computer data.
Formed from a resin, such as polycarbonate and coated with a highly reflective surface, usually aluminium.
Information is imprinted as a series of microscopic pits on the reflective surface.
EXIT
COMPACT DISK (CONT.)
Master disk is created using a finely focussed, high intensity laser.
Master is used to make copies.
A top coat of clear lacquer(coloured varnish) dissolved in alcohol protects the pitted surface from dust and scratches.
Low powered laser in the drive unit is used to read information on the disk.
EXIT
COMPACT DISK (CONT.)
The laser shines through the clear protective coating while a motor spins the disk past it.
When it encounters a pit, the intensity of the reflected light of the laser changes.
Change is detected by photo sensors and converted into a digital signal.
Data can be addressed by track and sector.
EXIT
It can store upto 700 MB of data.
Non erasable disk used for storing computer data.
One small disk can store the contents of the 33 volumes of the Encyclopedia Brittanica and have room to spare.
Types: Read only, Writable, Erasable.
EXIT
DVD
EXIT
LOCAL AREA NETWORK
A group of internally connected computers is called computer network. When the computer network is established in the limited area, it is called Local Area Network.
The computers are connected with the help of ETHERNET (LAN) CARD and data supply cables.
The main computer of the network is called SERVER and the other connected computers are called CLIENTS.
The SERVER stores the data which is supplied from the CLIENT computers.
EXIT
MODEM
Voice modems are used to transfer speech files.
Can be installed Internally as a card on the Motherboard.
Also as a external device because they are easy to communicate where telephone lines are not proper.
EXIT
EXIT
MEMORY
EXIT
NORMAL
Extended Data Out = another type of DRAM used in memory modules. Faster and more expensive than standard RAM.
Dynamic RAM (TRANSISTOR) = most common type used. Also the slowest and cheapest type of memory still used.
Static RAM = VOLATILE(LASTS TILL POWER IS ON)
EXIT
RAM (CONT.)
Video RAM = another type of DRAM used on video cards. Increases movie clarity and is faster than standard DRAM.
Synchronous DRAM = faster and more expensive type used in processor cache memory.
Synchronous Graphics RAM = type of SDRAM used primarily in video graphics cards.
EXIT
RAM (CONT.)
Error Correcting Code = very reliable and more expensive type of EDO RAM. Used primarily on network file servers and high-end workstations.
Multibank Dynamic RAM = is speedier and more efficient processing. Called Multibank because they have double the number of storage banks.
Fast Page Mode DRAM = is slightly faster than standard DRAM.
EXIT
ROM (Read Only Memory)
Programmable ROM = Once the chip has been programmed , the recorded information can’t be changed.
Erasable PROM = can be programmed or reprogrammed usually by exposing a normally covered sector to ultra-violet light. When in use, information can be “read” and the information remains on the chip until it is erased.
Electrically EPROM = is a special type of chip used to store BIOS programs. Under normal circumstances, the program stored is permanent. This is what happens to Flash BIOS.
EXIT
VIRUS
EXIT
VIRUS
Are a sad fact of life.
Only way is to catch is to copy and run an uninfected program.
Internet and E-mail downloads are responsible for 75% of all viruses.
Simple remedy is to take data backups regularly.
Another remedy is using Anti-Virus software.
EXIT
binary program file attached to e-mail (word document containing macro).
internet through Java Applets and Activex modules.
EXIT
scan the hard disk and floppy disk and detect viruses.
this program checks for a known number of viruses.
checks all the files on the disk that has been specified and reports if it finds any.
then user can either delete the infected file or let the anti-virus software do it.
EXIT
destroys viruses which they are programmed to detect.
some virus scanners reside in computer’s memory and check the entry of virus after every input / output operation.
on detection, a warning is displayed and all further operations are suspended.
EXIT
EXIT
Browsers
Simply put, a browser is a software application that lets you view pages on the Internet. Type the URL in the address bar of the browser, and it pops up the page for you. The browser gets the address translated into an IP address (the address of the server hosting the Web site), using the DNS. Thereafter, it forms a connection with that server and procures the necessary information, which is usually in the form of hypertext. Next, it reads the information, formats the page accordingly to display it on the screen. Some of the popular Internet browsers include Internet Explorer, Netscape Navigator, Opera, etc.
EXIT
Domain Name
Every computer on the Internet has its own unique IP address, which is in the form of numbers, e.g., 208.164.1.220.The system of domain names saves the trouble of remembering IP address of Web sites that need to be accessed. Domain names are recognisable words such as www.thinkdigit.com that represent a Web site or computer on the Internet.
First, the Internet browser translates the domain name typed in the address bar into the correct IP address. This is known as domain name resolution, and the system that makes this work is called the Domain Name System (DNS). There are 13 root servers distributed globally which perform this task. The object of the DNS is that anyone connected to the Internet can reach a particular site, or send e mail simply with the correct domain name.
For this to work, every domain name must be unique. Having two Web sites with the same domain name would make the system unpredictable and unreliable. This uniqueness makes it a reliable system with universal resolvability. Ensuring this universal resolvability is a non profit independent organisation known as Internet Corporation for Assigned Names and Numbers (ICANN). ICANN manages distribution of unique IP addresses and maintains the root servers that store information about all the top level domains (.com, .net, org, etc., and country specific names such as .co.in).
EXIT
File Transfer Protocol
FTP is a protocol developed for transferring files over the Internet
Based on TCP/IP, it is one of the most reliable and fastest file transferring methods, and is compatible with all types of systems be it PC, Mac, or UNIX.
Some of the most common FTP commands such as GET, PWD and PUT are supported by almost all operating systems. Though a user can use these commands at the command line, they are mainly intended for use in programs. Most of the servers that facilitate file downloads are based on the FTP protocol. HTTP an improvement over FTP supports a display of HTML pages with images and graphics along with support for file download.
EXIT
Home Page
On the Internet, Home Page could mean one of two things:
Every Web site has its own home page the first page a user views when he or she visits the site. For example, when you type www.thinkdigit.com into a browser, you are greeted with the site's home page. They can have access to all of the site's content from there.
A home page could also be a user's personal start page that opens when he or she launch their browser or press the browser's home button. This could be any Web page on the Internet, or a customized file on the local hard disk. This could also be set to a blank page. Web portals such as MyWay.com allow you to customize your start pages by delivering the content you want directly to your personal start page.
EXIT
Hyper Text Transfer Protocol
Hyper Text Transfer Protocol (HTTP) was developed to transfer text, images and files embedded in HTML tags over the Internet. Hypertext mainly includes links that lead from one page to another page, and Web browsers such as Internet Explorer, Netscape Navigator, etc., helps a user to browse through these links. A user can also direct a browser to a Web page by typing in a Universal Resource Locator (URL) in the address bar. A software known as HTTP server runs on the machine that hosts the Web pages. Upon receiving a request from another machine, it sends the information across. A browser at the receiving end converts the data received from the server into HTML pages, and displays it to the user.
EXIT
Web hosting
Web sites are saved on Web servers, from where users surfing the Internet can access them. Here's how it works. A user types a URL into his or her Web browser. The browser finds the physical location of the URL the server's IP address, gets the page from that server and renders it for the user. Most Web sites cannot afford their own server with the requisite high speed Internet connection. Hence, companies offer a service called hosting wherein they set up servers and let out a fixed amount of space for a Web site to use. Many Web sites maybe hosted on the same server. Hosting charges are based on the amount of server space taken up and the amount of bandwidth used. The amount of traffic depends on the number of people who have read those pages off the server. Contracts are for specific time periods generally a year. One or more e mail boxes may also be bundled along.
The actual URL of the Web site the domain name has to be registered with a registrar such as Network Solutions. This is an additional expense. Generally, the same company will offer you a bouquet of services such as domain registration, hosting, e mail and Web site creation.
EXIT
Web Site
Put simply, a Web site is a collection of (Web) pages that are related in some way, and placed in a distinct structure. A Web site could be about a company and its services, or a personal page about the creator and his or her specific interest. It could also be a Web site offering services such as news or downloads. Web pages are built on a markup language called Hyper Text Markup Language (HTML). Users can access Web pages through a Web browser that reads the code off the Web server and draws (renders) the page for display to the user. Web sites always have a home page or a starting address that is advertised or published. Web sites are not to be confused with a Web server. A server is a physical computer that serves pages. A large and complex Web site such as Microsoft.com would have different parts of the Web site on different servers, in different locations. The user accessing the Web site does not know whether the server is at the other end of the town, or the other end of the world it's seamless.
A site is said to be 'hosted' on a server and companies that provide space on their servers perform a service called hosting.
EXIT
Active Server Pages
Active Server Pages (ASP), is a Microsoft technology that is used to create dynamic Web pages. It means the pages are not static as with HTML pages, but are created on the fly according to what is to be shown to a particular visitor. An example, where this is needed, is Web based e mail services such as Yahoo!
The ASP technology is marketed by Microsoft along with its Internet Information Server (IIS). There have been four major versions of ASP ASP 1.0 (which was distributed with IIS 3.0), ASP 2.0 (which was distributed with IIS 4.0), ASP 3.0 (which was distributed with IIS 5.0) and ASP.NET, which is part of the Microsoft .NET platform.
Before ASP.NET, it was possible to create pages by mixing ASP server side code with HTML and client side scripting code. The result was an HTML code that could be viewed by your browser. With ASP .NET, support for .NET languages such as C# is introduced. Now, Web pages can be created using the Visual Studio .NET classes, as well as by normal scripting like the old days.
The close competitor to ASP is PHP, which is a free server side scripting technology.
EXIT
Broadband
A broadband medium is the one that simultaneously carries several channels that are separated using frequency division multiplexing.
This term is also used as a synonym for broadband Internet connection. A broadband Internet connection is one that has connection speeds above the normal dial up and ISDN connections, i.e., speeds above 128 kb/s. In some countries, the speed goes up to 1 Mb/s for home users and even higher for business users. These high speeds make it possible to have higher data transfer rates as well as higher performance while streaming data such as audio and video streams. It also makes it possible to use P2P file sharing software.
EXIT
Cookie
A cookie is a small file that websites place on your computer's hard disk. It stores information about your previous visits to the site. Cookies are supposed to make your web experience better. For example, when you visit online forums and read some posts, a cookie will be placed tracking this. The next time you visit, the cookie will be read. New posts since the last time you visited can be marked as new, so you won't waste time on items that were there the last time you visited. Other applications of cookies are web sites that 'remember' what type of content you like and show you only that, like a news web site that shows you only your local news, weather, and your personal stocks. Even advertisers use cookies so that they don't keep showing you the same ads.
Privacy groups fear that cookies could be used to invade our privacy. Some privacy software let you remove all your cookies. Or you could just find the files and erase them manually.
EXIT
E mail
E mail or email stands for electronic mail. More and more companies and individuals are making extensive use of e mail because it's cheap, fast, flexible, and reliable.
Any electronic document as well plain text can be sent over the Internet through e mail. Most e mail systems have a text editor for users to enter text messages and attach other files to the message. The e mail address is composed of two parts that are separated with the '@' sign. The second part is the name of the server that hosts the user's electronic mail box and the first part is the username on that server. For example, [email protected] has 'something.com' as the name of the server and 'someone' as the username.
Let's consider a mail sent from [email protected] to [email protected]. First, the user 'abc' logs onto the server 'xyz.com', composes his message and sends it. The server 'xyz.com' will send this message to 'something.com'. The server 'something.com' stores this email in 'someone's' mail box. The user 'someone' will be able to read the message when he or she logs on to the server 'something.com'. He can then read it, delete it, forward it or get it printed.
There are two kinds of e mail accounts Web based mail accounts and POP mail accounts. Web based mail accounts, such as those provided by Yahoo!, need the user to log on to the server whenever he or she wants to read or send emails. In the case of POP mail accounts, the mails are downloaded to the user's computer using such software as Outlook.
While composing a message, specify the address of the receiver in the 'To' field. More than one address can be specified using a comma or semicolon. Any address mentioned in the Carbon Copy (CC) field, will be seen by all the recipients in the mail header. Addresses specified in the blind carbon copy (BCC) field are not shown in the mail header.
EXIT
Firewall
A firewall is a system that prevents unauthorised access to or from a private network. It examines each message entering and leaving the network, and allows only those authorised messages to pass through. It can be implemented in hardware, software or both.
Some of the firewall techniques used are as follows:
Packet filtering: In this technique, each packet entering or leaving the network is examined and filtering is done on the basis of user defined rules. Though this technique is effective, but is difficult to setup. In addition, it is vulnerable to IP spoofing.
Application gateway: Only specific applications such as FTP and Telnet servers are observed. Though it is very effective, it can lead to performance degradation.
Circuit level gateway: Here, security mechanisms are applied only when a TCP or UDP connection is being established. Once connected, data can flow through the connection without being checked.
Proxy server: In this technique, all messages entering and leaving the network are intercepted. The true network addresses are hidden.
Usually, two or more of these techniques are used to implement a firewall.
EXIT
Instant Messaging
Instant Messengers (IM) exchange short text messages instantly between users who are online. All you need to do is download and install the chat software, register, and add a couple of friends. Once your contacts come online, you will be informed, and you're ready to chat.
The first popular tool was created by 3 Israelis in late 1996: ICQ (short for 'I Seek You') is an instant messaging tool that makes it simple for its users to communicate with other ICQ users. There are four big players in the IM space today ICQ, Microsoft's MSN Messenger, Yahoo! Messenger, and AOL's Instant Messenger (AIM). MSN grew in popularity because of its simplicity, and its tight integration with its ubiquitous Hotmail service. Similarly Yahoo! and AIM have capitalized on their strong user base to grow their popularity. Groups of friends, or departments in the office, generally have a preference towards one IM. Interoperability or better still a common standard, would greatly increase the value of the entire IM community. There are 2 solutions to this. Over time a common standard will be developed, or you could use a tool which works with all the networks together such as Trillian.
Apart from text messaging, today's IM clients provide the basis for much richer forms of communication. Voice and even video can be carried over the same networks.
EXIT
Internet
The Internet is a collection of millions of computers interconnected over a network. It was started as a small network by ARPA (Advanced Research Project Agency) for the US government in 1969 and it was known as ARPANET. Later, this design was used to create the Internet (or Net) as we know it today. The Net is based on the TCP/IP protocol, and uses resources similar to telecommunication networks. Unlike intranet, the Internet is completely decentralized by design. Every computer connected to the Net is independent, and you can decide what Internet services you want or don't want. To connect to the Internet, you have to contact an Internet Service Provider (ISP); the ISP gives you access to the Internet through their gateway.
E mail (electronic mail) and IM (instant Messaging) are some of the most popular Internet based applications.
EXIT
Spam
Spam is unwelcome e mail that you get from people you don't know. It often promotes dubious products, promises of a free trip to Hawaii, a better love life, get rich quick schemes, free pornography, etc. These often overwhelm your inbox and overload e mail systems, raising the maintenance cost.
There are certain practices that help reduce the amount of spam you receive they vary in effectiveness and ease of use. The first thing to do is to create two e mail IDs; a personal one for friends, family and colleagues, and a second public ID for the rest of the online world. Give the public ID to Services that require your e mail address, such as newsletters or message boards. Another option is to use the filter offered by most e mail clients and services. These let you sort your inbound e mail according to the address of the sender, directing the mail sent by someone on your address book into a separate folder, while another folder holds the mail that has originated from an unknown source. Finally, there are software solutions that protect you against 80 per cent of spam. These work as blacklists: databases with addresses that are known to generate spam mail.
EXIT
Telnet
Telnet is a tool for remotely logging on to a computer. It is based on the TCP/IP protocol, and allows one to use a remote computer just like a regular computer, provided that you have been given the necessary access rights to the programs and data present on that system. When you login using telnet, the remote system asks for your username and password. Based on that, one gets access to the system. You can then enter commands on your system that will be executed on the remote system.
For example, \"telnet computername\" logs you on to the computer called \"computername\".
This tool is now mainly used for remote administration the administrator can configure a server remotely over a network.

ABOUT COMPUTER

Documents

Transcript of ABOUT COMPUTER