Saturday, May 19, 2012

Class XI, INFORMATION TECHNOLOGY, "Data Presentation"

The set of symbols to express quantities as the basis of counting is referred to be a number system. There has been various number systems under human use for the purpose of counting and measurement. For instance decimal number system, octal number system, binary number system and hexadecimal number system have been most popular number systems which human beings have been utilizing for the purpose of counting and measurement.
Though a computer can process only binary numbers i.e. only 0 and 1, we give a brief account of each of the number system mentioned above. Inter conversion of these number systems would also be discussed in this chapter.
Decimal Number System
This is the most commonly used number system and which is very natural to man, hence very easy to use and remember. It consists of ten digits, i.e. from 0 to 9. As the total number of digits used in a number system is called its base or radix, hence base of radix of decimal number system is said to be ten.
Binary Number System
The base or radix of binary number is two, implying that there are only two digits 0 and 1 used in binary number system. This number system has become most popular system because of its use by the computers for processing data.
Octal Number System
This number system is consist of eight i.e. 0,1,2,3,4,5,6 and 7. Hence the base or the radix of octal number system is eight. Actually this number is a short hand version of binary numbers, Hence one octal represents three binary digits.
Hexadecimal Number System
Hexadecimal numbers are extensively used in microcomputers. As they are much shorter than binary numbers, hence easy to write and remember. They are also a short hand version of binary numbers. The hexadecimal also called Hex is equivalent to four binary digits. This number system consists of 0,1,2,3,4,5,6,7,8,9, A,B,C,D,E and F. The base of this number system is 16. The symbol A……..F stand respectively for 10…..15.
Binary to Decimal Conversion
All the number system may be easily converted into other number systems. In order to convert binary numbers into decimal numbers we multiply each bit of a particular binary number with (n-1) power of 2.
Add all the resultant multiplied bits.
Example No. 1
To convert the binary number 10010 to a decimal number we proceed as follows:
100102 = (1 x 24) + (1 x 23) + (1 x 22) + (1 x 21) + (1 x 20)
= (1 x 16) + (0 x 8) + (0 x 4) + (1 x 2) + (0 x 1)
= 16 + 0 + 2 + 0
= 18
It should be kept in the mind that any number raised to the power 0 equals 1.
Example No. 2
Similarly in order to convert the binary number 110111 to a decimal number we may proceed as follows:
1101112 = (1 x 25) + (1 x 24) + (1 x 23) + (1 x 22) + (1 x 21) + (1 x 20)
= (1 x 32) + (1 x 16) + (1 x 8) + (1 x 4) + (1 x 2) + (1 x 1)
= 32 + 16 + 0 + 0 + 4 + 2 + 1
= 56
Example No. 3
If there is a period (.) in the binary number e.g. (1011.10). Then the conversion of such binary number can be illustrated as follows:
(10112) = (1 x 23) + (1 x 22) + (1 x 21) + (1 x 20)
= (1 x 8) + (0 x 4) + (1 x 2) + (1 x 1)
= 8 + 0 + 2 + 1
= 11
(.102) = (1 x 2-4) + (1 x 2-2)
= (1 x 1/2) + (1 x 1/4)
= 1/2 + 0 = 0.5
Hence (1011.102) = 11.5
Decimal to Binary Conversion
A decimal number can easily be converted to a binary number. For this purpose we take following steps.
1. Divide the decimal number by 2 and note down the remainder.
2. Take the quotient and again divide by 2, then note down the remainder again.
3. Repeat the 2nd step unit you get 1 as the quotient.
4. The remainders in the reverse order would be our required binary number.
Example No. 4
For example in order to convert decimal number 15 to binary number. we may proceed as follows.
15/2 = 7 and the remainder is 1
7/2 = 3 and the remainder is 1
3/2 = 1 and the remainder is 1
1/2 = 0 and the remainder is 1
Hence the required binary number is 1111
Converting Decimal Fractions to Binary Numbers
The most simple method of converting fractional decimal numbers to binary number is repeated multiplication by two. In this method numbers to the right of the decimal point are repeatedly multiplied by 2 till we get a whole number. The product in fractions is assigned as 0 bit while in whole number it is assigned as 1 bit.
The process of converting a fractional decimal number to binary number would be explained by the following example.
Example No. 5
Let us suppose the we want to convert 0.125 in a binary numbers then proceed as follow.
0.125 x 2 = 0.250 it carries 0
0.250 x 2 = 0.500 it carries 0
0.500 x 2 = 1.00 it carries 1
Hence we can conclude that (0.125)10 = (0.001)2
Addition to Binary Numbers
In order to add binary number below given table should be kept in mind
0 + 0 = 0
0 + 1 + 1
1 = 0 = 1
1 + 1 = 0 with a carry of 1
The following example will illustrate the addition of binary numbers.
Example No.6
Add 1001 and 1010
1001 + 1010 = 11011
Subtraction of Binary Numbers
In order to subtract a binary number from another binary number you must keep the following table in your mind.
0 – 0 = 0
1 – 0 = 1
1 – 1 = 0
0 – 1 = 1 with a barrow of 1
The process of binary subtraction an be illustrated with the help of example given below
Example No. 7
For subtracting binary number 101 from 1001 we proceed as follows
1001 – 100.1 = 1.11
Octal to Decimal Conversion
For converting an octal number to a decimal number we use the same sort of polynomial as was used in the binary case. However in octal to decimal conversion the base or radix is 8 instead of 2.
The process of converting an octal number into a decimal number would be clarified with the help of following example.
Example No. 9
The Octal number 2134 can be converted into decimal number by proceeding as follows
(2134)8 = (2 x 83) + (2 x 82) + (2 x 81) + (2 x 80)
= (2 x 512) + (1 x 64) + (3 x 8) + (4 x 1)
= 1024 + 64 + 24 + 4
= 1116
Hence (2134)8 = (1116)10
Example No. 10
The octal number 1.123 can be converted to decimal number as follows
(1.123)8 = (1 x 80) + (1 x 8-1) + (1 x 8-2) + (1 x 8-3)
= (1 x 1) + (1 x 1/8) + (1 x 1/64) + (3 x 1/512)
= 1 + 1/8 + 2/64 + 3/512
= 1 83/512
Decimal to Octal Conversion
For converting decimal number to octal number. we apply a method of repeatedly dividing decimal by 8 and use each reminder as a digit in the octal number. The process of converting decimal to octal number may be illustrated by the following example.
Example No. 11
To convert the decimal number 429 to octal number we process as follows
429/8 = 53 Reminder is 5
53/8 = 6 Reminder is 5
6/8 = 0 Reminder is 6
Hence (429)8 = (655)10
Octal to Binary Conversion
As we have mentioned earlier that octal number system is a short hand version of binary numbers and one octal represents three binary digits as shown by the following table
Equivalent Octal and Binary Number
Octal 0
In order to convert an octal number to a binary number we just replace each octal digit with the appropriate three bits. This produce an be explained with the help of following example
Example No. 12
(25)8 = (010101)2
Because (2)8 = (010)2 and (5)8 = (101)2 as shown by the above table

Class XI, INFORMATION TECHNOLOGY, "Computer Network"

Computer Network
In connection with the information technology and computers a network is a way to connect computers together so that they can communicate, exchange information and pool resources or a network is a communicating system connecting two or more computers. Network connects people as close as the next office and as for as halfway around the world.
In business networks have revolutionized the use of computer technology. Many businesses that used to relay on a centralized system with mainframe and a collection of terminals now use computer networks in which every employee who needs a computer has personal computer connected to the network. In education, schools, colleges and universities have also shifted to strategies built around networked personal computers.
Configurations or Topologies Networks
A network can be arranged or configured in several different ways. This arrangements is called the network’s topology. The four principal network topologies are
1. Star Network
2. Bus Network
3. Ring Network
4. Hierarchical Network
1. Star Network
In a star network small computers or peripheral devices are linked to a central unit. This central unit may be a host computer or a file server. All the communications pass through this central unit. Control is maintained by polling. Each device is in turn allowed to send the message.
One particular advantage of the star form of network is that it can be used to provide a time-sharing system. i.e several users can share resources (time) on a central computer. The star is a common arrangement for linking several microcomputers to a mainframe that allows access to an organizations database.
2. Bus Network
In a bus network each device in the network handles its own communication control. There is no host computer. All communications control travel along a common connecting cable called a bus. As the information passes along the bus it is examined by each device to see if the information is intended for it.
The bus network is typically used when only a few microcomputers are to be linked together. The bus network is not as efficient as the star network for sharing common resources. However it is less expensive and is in very common use.
3. Ring Network
In a ring network, each device is connected with two other devices forming a ring. There is no central file server or computer. Messages are passed around the ring until they reach correct destination. With microcomputers ring network is the least frequently used arrangement. However it is often used to link mainframes specially over wide geographical areas.
A ring network is useful in a decentralized organization because it makes possible a distributed data processing system i.e. computers can perform processing tasks at their own dispersed locations.
4. Hierarchical Network
This type of networks are also called hybrid network. It consist of several computers linked to a central host computer just like a star network. However these computers are also hosts to other smaller computers or to peripheral devices. The host at the top of the hierarchical network could be mainframe. The computers below the mainframe could be minicomputers and those below microcomputers. This network allows various computers to share database processing programs and different output devices. It is useful in a centralized organizations.
Strategies of Networks
Every network has a strategy or a way of coordinating the sharing of the information and resource. The most common network strategies are terminal, peer-to-peer and client/server systems, terminal network system. In this system processing power is centralized in one large computer, usually the mainframe. The nodes (a node is any device connected to network) connected to this host computer are terminals (a terminal is a input or output device) with little or no processing capability. Most airline reservation systems are terminal systems.
Peer-to-Peer Network System
In a peer-to-peer network, nodes can act both as servers and clients. There are several advantages of using this type of strategy. The networks as inexpensive and easy to install and they usually work well for smaller systems with less than ten nodes. As the number of nodes increases, however the performance of the network declines.
Client/Server Network System
Client/Server network system uses to coordinate and supply services to all other nodes on the network. The server provides access to centralized resources such as databases, applications software and hardware. This strategy is based on specialization. Server nodes coordinate and supply specialized services and client nodes request services.
One advantage of client/server network system is its ability to handle very large networks efficiently. Another advantage is the powerful management software that monitors and controls networks activities. The major disadvantage of it is the high cost of installation and maintenance.
Advantages of Network
Networks provide tremendous benefits. The most compelling advantages of network are as follows.
1. Networks allow users simultaneous access to shared programs and data.
2. Network also allows users to share peripheral devices such as printers and hard disks.
3. Network usually includes the capacity to send e-mail and many e-mail systems let users to attach files to their messages.
4. Connecting computers to form a network makes it easier to perform backups of the data on all the network hard disks.
Types of Networks
Communications differ in geographical size. Three important types are LANs, MANs, WANs.
Local Area Networks (LANs)
Network with computers and peripherals devices in close proximity within the same building are called local area networks (LANs).
The figure shows an example of a LAN. This type of arrangement has two benefits.
1. People can share different equipment, which lowers the cos of equipment.
2. LAN also features a network gateway. i.e. a LAN may be linked to other LANs or to large networks in this manner.
Metropolitan Area Network (MANs)
These network are used as links between office buildings in a city. Cellular phone systems expand the flexibility of MANs by allowing links to car phones and portable phones.
Wide Area Network (WANs)
Wide area networks are countrywide and worldwide networks. Among other kinds of channels they use microwave relays and satellites to reach users over long distances. One of the most widely used WANs is Internet. Which allows users to connect to other users and facilities worldwide.
Uses of Internet
The most common uses of Internet are
1. Communicating
Sending and receiving e-mail is the most popular internet activity. You can send and receive e-mail to and from you friends and family located almost anywhere in the world. You can join an listen to discussions and debates on a wide variety of special interest topics.
2. Shopping
One of the fastest growing applications of Interest is electronic commerce. You can visit a cyber mall for making purchases.
3. Researching
Internet provides you to have one of the world’s largest libraries available from home.
4. Entertainment
Do you like music, the moves and reading or playing computer games? You can find them all on Internet waiting for you to locate and enjoy

Class XI, INFORMATION TECHNOLOGY, "Computer Software and Programming Languages"

An information system has five parts. People, procedures, software, hardware and data. Software which is one of the most important part of an information system. Is an other name for a program or programs. Program is the step by step instructions that tell the computer how to do its work. The purpose of a software is to convert data (unprocessed facts) into information (processed facts). In most cases, words software and programs and interchangeable.
There are two major kinds of software-application software and system software.
Application software are the software the users of the computer use. Whereas system software are used by the computers.
Application Software
Application software may be describe as end-user software. They perform useful work on general-purpose tasks such as word processing and cost estimating.
Application software may be
1. Packaged
2. Custom Made
1. Packaged Software
Packaged Software are the programs prewritten by professional programmers that are typically offered for sale.
2. Custom-Made Software
Custom-Made or Custom programs are the programs written for a specific purpose and for a specific organization. Using computer languages, programmers create this software to instruct the company’s computer to perform whatever tasks the organization wants.
There are certain general purpose programs which are called “basic applications” The most popular basic tools are
  • Word Processing Programs used to prepare written document.
  • Spreadsheets Programs used to analyse and summarize numerical data.
  • Database Manageers used to organize and manage data and information.
  • Presentation Graphic Programswhich are used to communicate a message.
  • Personal Information Management Programs used to organize and schedule activities.
  • Integrate Programs which combine some or all of these applications in one program.
Summary of Basic Application Software
The summary of the basic application software mentioned above has been given below. Which shows various software designed by well known software publishers. Microsoft, Lotus and Corel.
Basic Applications
  • Word Processors = Microsoft Word, Lotus, Word Pro, Corel WordPerfect
  • Spreadsheets = Microsoft Excel, Corel Quattro Pro, Lotus-2-3
  • Database Managers = Microsoft Access, Corel Paradox, Lotus Approach
  • Presentation Graphics = Microsoft PowerPoint, Corel Presentation
  • Personal Information managers Microsoft Outlook, Lotus Organizer
  • Integrated Packages = Microsoft Work, Lotus Works.
  • Software Suites = Microsoft Office 97, Corel Office 97
Common Features of Basic Application
As all the above mentioned categories of software are designed to be used by many people to perform most common kinds of tasks we call them basic applications. Most common application software have some common features. The most important of them are given below.
Almost all software packages have menus to present commands. Typically menus displayed in a menu bar at the top of the screen when one of the item is selected a pull down menu appears.
This is a list of commands associated with the selected menu.
Shortcut keys
Many applications also have shortcut keys for frequently used commands. Many of the shortcut keys are function keys. F1, F2 and so on. Others shortcut use key combinations typically consisting of the Alt, Ctrl or Shift key used in combination with a letter number or function key. For example in Word97 the short cut key F7 starts the spelling tools and the key combinations of shift and F7 starts the Thesaurus tools.
Toolbars are typically below the menu bar. They contain icons or graphic representations for commonly for commonly used commands.
For most applications packages one of the menus on the menu bar is Help. This typically include a table of contents a search feature to locate reference information about specific commands and access to specific learning features such as tutorials and step-by-step instructions.
Dialog Boxes
Dialog boxes frequently appear after selecting a command from a pull down menu. These boxes are used to specify additional options.
Scroll Bars
Scroll bars are usually located on the right and / or the bottom of the screen. They enable user to display additional information not currently visible on the screen.
The ability to change or edit entries is a feature common to almost all applications. The edit feature makes revising and updating easy and is one of the most valuable features.
Save and Print
Common to all applications software is the ability to save or store your work as a file on a floppy or hard disk. This allows user to open and use the file at a later time in case user wants to add or modify the document. In addition all applications allow user to a copy of his document on paper.
Word processing programs and spreadsheets program are most commonly used categories of application software hence we explain them in much more detail.
Word Processors
word processing software creates text-based documents such as letter, memos, term papers and reports. Once it was thought that only secretaries would use word processors. Now they are used extensively in managerial and professional life. Indeed, it has been found that among the basic software applications. Word processors are most important software used by common people.
Popular word processing packages include Microsoft Word. Corel WordPerfect and Lotus Word Pro as shown in the above summary of basic applications.
Important Features of Word Processors
Some important features shared by most word processors are as follows
Word Wrap and the Enter Key
One basic word processing feature is word wrap i.e. word processor automatically moves the insertion point to the next line once the current line is full. The begin a new paragraph or to leave a blank line Enter key is pressed.
Spelling and Grammar Checkers
Many word processors include a spelling checker feature that identifies typing errors. For example Word97 identifies misspelled words with a red wavy underline. Similarly grammar checkers can be run that will identify poor wording excessively long sentences and incorrect grammar.
Text can be aligned within the margin in various way. The most common alignment is left alignment.
Text can be enhanced in a variety of ways including adding basics formatting such as bold, under line and italics.
Besides above mentioned feature other common features of word processors are References, Search and Replace, Tables, Hyperlinks, Thesaurus, Graphics, Internet publishing and Workgroup.
Spreadsheets is an electronic worksheet used to organize and manipulate and display option for “what-if” analysis. Spreadsheets are used by financial analysts, accountants, contractors and other concerned with manipulating numeric data.
Popular spreadsheets packages include Microsoft Excel, Quattro Pro and Lotus 1-2-3 as shown by above summary.
Common feature of Spreadsheets
Like the word processors, spreadsheets designed by various software publishers share following common features.
Formulas and Functions
Formulas are the instructions for calculations. They calculate result using the numbers in reference cells. Whereas functions are prewritten formulas that perform calculations automatically.
The recalculation feature can be used to analyze the effect of changes to the spreadsheets.
Analytical Graphs
To help visualize the data in spreadsheets user can create analytical graphs or charts.
One of the newest additions to spreadsheets applications is the workgroup program which allows multiple users to collaborate electromically on spreadsheet.
Linked Files
Most spreadsheets programs allow users to link cells in one worksheet file to cells in other worksheets in the same file or to other worksheet files. Whenever a charge occurs in one file the linked cells in the other worksheets are automatically updated.
Advanced Application Programs
Besides above mentioned basic application programs there are certain programs which are called “advanced applications”. These are more specialized than the basic application. These programs are widely used in certain career areas. The most popular tools are:
Graphic Programs used to create professional publications and to capture and edit graphic images.
Multimedia used to integrate all kinds of information including video, audio, graphic and text into a single interactive presentation.
Web Publishers used to create interactive multimedia web page. Project management used to plan projects schedule people and control resources.
System Software
The user interact with the application software whereas system software enables the application software to interact with the computer hardware. System software is a “background” software. It includes programs that help the computer manage its internal resources.
Kinds of System Software
System software deals with the physical complexities of how the hardware works. System software consists of the following four programs.
1. Bootstrap loader
2. Diagnostic routines
3. Basic input-output system
4. Operating System
1. Bootstrap loader
The bootstrap loader is a program that is stored permanently in the computer’s electronic circuitry. When computer is turned on the bootstrap loader obtains the operating system from hard disk and loads it into memory. This is called booting the system.
2.Diagnostic Routines
These are also programs stored in the computer’s electronic circuitry. They start up when machine is turned on. They test the primary memory the central processing unit and other parts of the computer. Their purpose is to make sure the computer is running properly.
3. Basic Input-Output System
It consists of service programs stored in primary storage. These programs enable the computer to interpret keyboard characters and transmit them to monitor or to a floppy disk.
Operating System
The operating system is a collection of programs that help the computer to manage its resources. The Operating System takes care of lot of internal matters. For example it interprets the commands user gives to run programs. It manages memory data and file.
The most important system program is the operating system which interacts between the application software and the computer. The operating system handles such details as running (executing) programs, storing data and programs and processing data.
Microcomputer operating systems change as the machines themselves become more powerful and outgrow the older operating systems.
The most popular microcomputer operating systems are
DOS the original operating system for International Business Machines (IBM) and IBM compatible microcomputers.
Windows not an operating system but an environment that extends the capability of DOS.
Windows 95 a widely used operating system with the built-in internet support.
Windows 98 a new operating system with the intensive internet and multimedia support.
Windows NT a powerful operating system designed for powerful microcomputers.
OS/2 Warp the operating system developed by IBM for powerful microcomputers.
Macintosh Operating System the standard operating system for Apple Corporation’s Macintosh computers.
Unix an operating system originally developed for microcomputers that can run on many of the powerful microcomputers.
Disk Operating System
DOS’s original developer Microsoft Corporation sells it under the name MS-DOS. It was originally standard operating system for all microcomputers which were IBM compatible or DOS based.
1. Even today DOS is still widely used operating system.
2. An enormous number of application programs have been written for DOS. Indeed more specialized software is available for DOS for than any other operating system.
3. DOS runs on many computers, old and new that are cheap.
1. It can support very limited primary storage.
2. It can be used only for single-tasking and not for multi-tasking.
3. It uses character-based interface.
Windows 98
Windows like Windows 95, Window 98 and Windows NT is not a operating system, rather an operating environment. While Windows 95, Windows 98 and Window NT are operating systems. But Windows 98 is one of the most popular operating systems being used nowadays. It is an advanced version, designed for today’s very powerful microcomputers.
1. It is faster in many common tasks like starting up loading applications and shutting down. It includes a Tune-up wizard automatically monitors system operation and suggest ways to improve performance.
2. Windows 98 is fully integrated with Microsoft’s browser, Internet Explorer, making Internet access easier and faster.
3. Plug and play capability is extended to support the newest advance in technology. Multiple views of an application or multiple applications can be viewed on separate monitors simultaneously.
4. Windows 98 has advanced audio and video capability. With a tuner card, TV on microcomputers monitor can be watched.
1. Windows 98 requires at least a Pentium Microprocessor to operate effectively. Besides more hard disk space and memory are necassary.
2. Fewer applications have been written specifically for it. It can however run most DOS, Windows and Windows 95 applications.
Language is a system for representation and communication of information or data. Like human beings, a language or signal is required to communicate between two persons. Similarly, we cannot obtain any result by computer without langtage. Computer does not understand directly what we are communicating with computer as English or Arabic, it understands only machine language (binary codes 0-1). Computer translates English language into machine codes through interpreter then process instructions and give us the results.
The computer languages can be divided into two main levels.
Machine language (0-1)
Symbolic language (A-Z)
Symbolic languages are further divide into two main levels
High-level language
Low-level language
Although computers can be programmed to understand many different computer language. There is only one language understood by the computer without using a translation program. This language is called the machine language or the machine codes. Machine codes are the fundamental language of the computer and is normally written as strings of binary 0-1.
Programs written in machine language can be executed very fast by the computer. This is mainly because machine instructions are directly understood by the CPU and no translation of program is required.
However, writing a program in machine language has several disadvantage.
Because the internal design of every type of computer is different from every other type of computer and needs different electrical signals to operate. The machine language also is different from computer to computer.
Although easily used by the computer, machine language is difficult to program. It is necessary for the programmer either to memorize the dozens of code number for the commands in the machine’s instruction set or to constantly refer to a reference card.
It is difficult to correct or modify machine language programs. Checking machine instructions to locate errors is difficult as writing them initially.
In short, writing a program in machine language is so difficult and time consuming.
In symbolic languages, alphabets are used (a-z). symbolic languages are further divide into two main levels.
High level languages
Low level languages
A language which is one step higher than machine language in human readability is called Assembly Language or a low-level language. In an assembly language binary numbers are replaced by human readable symbols called mnemonics. Thus a low-level language is better in understanding than a machine language for humans and almost has the same efficiency as machine language for computer operation. An assembly language is a combination of mnemonic, operation codes and symbolic codes for addresses. Each computer uses and has a mnemonic code for each instruction, which may vary from computer to computer. Some of the commonly used codes are given in the following table.
Add – ADD
Subtract – SUB
Multiply – MUL
Compare Registry – CR
Compare – COMP
Branch Condition -BC
Code Register -LR
Move Characters -MVE
Store Characters -STC
Store Accumulator – STA
An assembly language is very efficient but it is difficult to work with and it requires good skills for programming. A program written in an assembly language is translated into a machine language before execution. A computer program which translates any assembly language into its equivalent machine code is known as an assembler.
A language is one step higher than low-level languages in human readability is called high-level language. High – level languages are easy to understand. They are also called English oriented languages in which instruction are given using words. Such as add, subtract, input, print, etc. high level language are very easy for programming, programmer prefer them for software designing that’s why these languages are also called user’s friendly languages. Every high level language must be converted into machine language before execution, therefore every high level language has its own separate translating program called compiler or interpreter. That’s why some time these languages are called compiler langauges. COBOL, BASIC, PASCAL, RPG, FORTRAN are some high level languages.
An interpreter is a set of programs which translates the high-level language into machine acceptable form. The interpreters are slow in speed as compared to compilers. The interpreter takes a single line of the source code, translates that line into object code and carries it out immediately. The process is repeated line by line until the whole program has been translated and run. If the program loops back to earlier statements, they will be translated afresh each time round. This means that both the source program and the interpreter must remain in the main memory together which may limit the space available for data. Perhaps the biggest drawback of an interpreter is the time it takes to translate and run a program including all the repetition which can be involved.
A compiler converts the programmer’s procedural language program called the source code into a machine language code which is called the object code. This object code can then be saved and run later. Example of precedural languages using compilers are standard versions of Pascal, COBOL, and FORTAN.
Another language that is widely used on microcomputers and easy to learn is Pascal, named after Blaise Pascal, a French mathematician. This language has become quite popular in computer science educational programs.
C is general purpose language that also works well with microcomputers. It is useful for writing operating systems, spreadsheets programs, database programs and some scientific applications. C++ is a version of C that incorporates object-oriented technologies.
COBOL which stands for Common Business-Oriented Language is one of the most frequently used programming languages in business. Through harder to learn than BASIC its logic is easier to understand for a person who is not a trained programer.
Short for FORmula TRANslation, FORTRAN is a widely used scientific and mathematical language. It is very useful for processing complex formulas. That’s why many scientific and engineering programs have been written in this language

Class XI, INFORMATION TECHNOLOGY, "Input Output and Storage Devices"

INPUT DEVICES Input devices are used to provide data or information to the computer. The computer follows the instructions given to it by and input device. A variety of input devices are used with the computer depending on the type and purpose of input information. For example, a keyboard is commonly used to transfer data or information from human readable form to machine readable form. Other examples of input devices are: mouse, joystick, trackball, light pens, digitizers, scanners, optical character reader (OCR), touch window, etc.
The mouse is an input device that usually contains one or two buttons. As a user moves the mouse on a flat surface, the mouse controls the cursor movement on the screen. When the user presses one of the buttons, the mouse either marks a place on the screen or makes selection from data or menu on the screen. A mouse has a sphere on its underside. This rotates as the mouse is moved along a flat surface.
The mouse translate the direction and speed of rotation into a digital signals that identifies the position or control, the cursor on the computer.
A mouse can be used for many application, ranging from games to drawing and designing products with computer graphics. It provides an alternative for people who are uncomfortable with a keyboard but it also can be used in combination with a keyboard to input data.
A Trackball is a pointing device almost like a mouse turned upside down. The user controls the cursor on the screen by rolling a plastic ball with a fingertip or wrist. To execute commands with a Trackball, one or more buttons are pressed, much in the same way as is done with a mouse. The cursor can be moved around on the screen by rolling the ball with a thumb or finger.
Trackball is popular among users of laptop computers when space is limited and may be mounted on either side of the keyboard. For handicapped people who may have difficulty pressing keys on a standard keyboard or using a mouse, the trackball may be the answer since it edoes not require to moves the entire arm to use it.
Scanner is an input device. It is also called Optical Reader or Digital Scanner. It scans or reads text and picture printed on a paper and enters them directly into the computer memory.
The advantage of a scanner is that the user needs not type the input data in. This is a lust and accurate method for entering data into the computer. The scanner takes electronic images, of text or pictures from the paper it breaks each image into light and dark dots and stores them into the computer memory in machine codes. Scanned text can be edited by OCR software. Optical Character Recognition (OCR) software translates the scanned document into text that can be edited.
The image scanner is useful because it translates printed images into an electronic format than can be stored in computer’s memory. The stored image can be transferred into a paint program or directly into a word processor. You can use software to organize and manipulate the electronic image.
A keyboard is the most commonly used input device which helps us in simply keying in required information in a computer. This information is subsequently stored in the computer’s memory. A keyboard can be used effectively to communicate with the computer but considered to be relatively slow as compared to other input devices. The keyboard is divided into following divisions:
These keys are similar to a standard typewriter and is used to type general information.
These keys are used to input numeric data only. These are very useful in case of large numeric data input because all numeric keys can be accessed by one hand only. These keys can also be used as an alternative to the screen navigation and editing keys.
These are keys marked as F1 – F12, located normally at the top of the keyboard. These are special keys provided to a programmer which allow him to attach special functions to each key. Each of these function keys are also given some special function in different packages.
These keys are provided to move around in the screen. May programs use these keys to let the user move around the screen display. In some keyboards these keys are also provided inside the numeric keypad as alternate keys.
The description of commands assigned to function keys under the BASIC mode.
F1 – LIST Function – Used to display the lines of your program on the screen.
F2 – RUN Function – Used to execute a program from its beginning.
F3 – LOAD Function – Used to read a program from a storage device and store it in main memory.
F4 – SAVE Function – Used to store a program on a storage device from Memory.
F5 – COUNT Function – Used to restart a program after it has temporarily interrupted by a stop or CTRL + BREAK.
F6 – LPT1 Function – Used to transfer data from the video screen to the line printer.
F7- TRON Function – Refers to “trace on”. This function causes the line number of program line to be displayed as these lines are executed.
F8 – TROFF Function – Refers to “trace off”. This function cancels TRON function.
F9 – KEY Function – Use to change the function of the other function keys.
F10 – SCREEN Function – Used to return program to the character mode from the graphic mode and a;so to turn off the colour.
An output device is used to display the data or information that we receive from the computer. An output device can be used to display or print the intermediate or final results performed by computer. A variety of output devices are used with computer. The use of these devices depends on the type and purpose of output. Some examples of output devices are: Monitors, Printer, Plotters, Visual display unit (VDU), liquid crystal display (LCD), etc.
To display result or output from computer, a T.V like device is used which is called monitor. The monitors are also referred as C.R.T (Cathode Ray Tube), V.D.U (Visual Display Unit). The monitor assist during input from the keyboard, this display is called a soft copy. The monitor can be of various kinds, depending on the type of application. Monitors are categorized into two groups:
Monochrome monitors
Colour monitors
Monochrome monitors are used specially for text editing purpose. These monitors can display only one colour. Normally amber, green or paper white.
Colour monitors serves a wide range of selection according to the application. Such as red, green, blue, Enhance Graphic Array (EGA), Colour Graphic Array (CGA), Video Graphics Array (VGA), Super Video Graphics Array (SVGA).
There are two types of colour monitors:
1. CRT Monitor
2. LCD Monitor
The CRT monitors are a lot like television set, using the same CRT or Cathorde Ray Tube technology. The CRT monitor has two major parts; the screen and the cathode ray tube (CRT). The screen is the front of the monitor and CRT is fitted inside the monitor.
Another monitor type is LCD or Liquid Crystal Display. LCD monitors are a lot like CRT monitors without the bulkiness but they do not have CRT. LCD monitors use a flat lightweight surface filled with millions of tiny glass bubbles, each having a phosphoric covering. These phosphoric coverings glow to create an image. LCD screens provide clarity and flicker-free viewing.
A computer peripheral that puts text or a computer generated image on paper or on another medium, such as a transparency. Printer can be categorized in several ways the most common distinction is IMPACT and NON-IMPACT.
Is the method used by the conventional type writers. In some type of impact printing a metal “hammer” embossed with a character strikes a print ribbon, which presses the characters image into paper. In other types the hammer strikes the paper and presses it into the ribbon characters created through impact printing can be formed by either a solid font or dot matrix printing mechanism.
Does not depend on the impact of metal on paper. In fact no physical contact at all occurs between the printing mechanism and the paper. The most popular non-impact methods today utilize thermal transfer, ink-jet.
Any printer that produces character made up of dots using a wire pin printed head. The quality of output from a dot matrix printer depends largely on the number of dots in the matrix, which might be low enough to show individual dots or might be high enough to approach the look of fully formed characters. Dot matrix printers are often categorized by the number of pins in the printer head typically, 9 or 24.
Any printer that prints one line at one time, as opposed to one character at a time or one page at a time. Line printer typically produce the 11 by 17 inch “computer” printout. They are high speed devices and are often used with mainframes, minicomputers, or networked machines rather than with single user system. Types of line printers include chain printers and band printer.
An electrophotographic printer that is based on the technology used by photocopiers. A focussed laser beam and a rotating mirror are used to draw an image of the desired page on a photosensitive drum. This image is converted on the drum into an electrostatic charge, which attracts and holds toner. A piece of electrostatically charged paper is rolled against the drum, which pulls the toner away from the drum and onto the paper. Heat is then applied to fuse the toner to the paper. Finally, the electrified charge is removed from the drum and the excess toner is collected. By omitting the final step and repeating only the toner application and paper handling steps, the printer can make multiple copies.
Daisy wheel printer are some times called letter quality printer because they are often used to produce attractive correspondence. The D.W.P is a flat circular device made of metal with character embossed on it. As this wheel spins at a very high speed the hammer hits the specific character against the ribbon which presses against the paper.
It is a kind of non-impact printer. In electrothermal printing, characters are burned on to a special paper by heated rods on a print heat. They transfer ink from a wax-based ribbon onto plain paper. These printer can support high quality graphic.
It is a kind of non-impact spray small dots of electrically charged ink onto a paper to form images. Ink jet printer are flexible enough to be used as plotters.
Plotter is a special output device, which is used to produce high quality, perfectly proportional hard copy output. Plotters are designed to produce large drawings or images such as construction plans for buildings or blue prints for mechanical devices. Plotters have been used in automotive and aircraft design, topological surveys, architectural layouts and other similar complex drafting jobs.
A plotter is composed of a pen, a move-able carriage, a drum and a holder for chart paper. Both the pen and the paper can move up and down and back and forth. This permits very detailed drawings. Some plotter having coloured pens can make coloured drawings also.
There are two types of plotters, which are as follows:
1. Drum Plotter
2. Flatbed Plotter
On the drum plotter, the pens, and the drum move concurrently in different axes to produce the image. Drum plotters are used to produce continuous output, such as plotting earthquake activity, or for long graphic output, such as structural view of a skyscraper.
On some flatbed plotters, the pen moves in both axes while the paper remains stationary. However, on most desktop plotters, both paper and pen move concurrently in much the same way as on drum plotters.
Secondary storage devices are also called backup storage because it is used to store data. Volume of data on permanent basis which can be partially transferred to the primary storage, when required for data processing. Afterwards these devices are comparatively cheap and provide greater space to store the data /instructions are stored on secondary storage devices in the same binary codes as in primary storage.
The storage capacity of the primary storage of today’s computer is not sufficient. To store a large volume of data as a result additional memory called secondary storage is needed with most of the computer system.
These devices also provides the fast communication than I/O devices. The internal memory of a computer is a volatile memory. Therefore, we cannot save the data permanently. In that case we require secondary storage device which provide the facility to store the data for future use.
Random Access Devices are those devices on which we can directly access the data. These devices are comparatively provide the fast communication.
For example, hard disk, floppy disk, optical disk.
A floppy disk, also called simply a diskette or disk, is a small flexible Mylar disk coated with iron oxide on which data are stored. The floppy disk has been around since early 1970s, today it is available in three 3½ inch, 5¼ inch and 8 inch sizes. The 5¼ and 8 inch diskettes are covered by stiff protective jacket with different holes. The central big hole called hub ring which is used to hold by disk drive during rotation. The elongated read write window is used to read and write data through read/write head. The small hole next to the hub ring is called index hole which is used to locating data through computer. The cut out on the side of the floppy disk is called write protect notch. If we cover this opening with a piece of paper then we can’t write data on to disk.
In small diskette a hard plastic cover and protective metal is used to protect disk. Before using a disk we have to format a disk in which disk is divided into tracks and sectors for storing the data. Diskettes may be double sided and single sided while the storage capacity become less or more.
Floppy diskettes are more convenient to use with microcomputers. A floppy disk which is a random access device can access data fast than magnetic tape.
Sequential Access Devices are those in which we can access the data one by one in a sequence. These devices provide slow communication as compared to Random Access Device.
Magnetic tape is a sequential access device about one half or one fourth inch in size and made of Mylar (a plastic material) coated with a thin layer of iron oxide. Data can be read and write through a device which is called tape drive. The read/write head of tape drive which is an electromagnetic component read, write and erase data from magnetic tape. Magnetic tape is divided into nine separate strips or tracks in which eight tracks are used to store data and ninth track is used for error checking bit.
Magnetic tape can store large quantities of data therefore they are erasable, usable and durable secondary storage device. But it can use with large computers.
Hard disk is a thin circular metal plate coated both side with a magnetic material. A hard disk pack consist of a number of disk mounted on central shaft which rotate at a speed of 2400 rpm or more. In a hard disk information is stored on both the surfaces of each disk plate except the upper and the lower surfaces of the bottom plate which are not used. Information is recorded on the track of the disk surfaces in the form of invisible tiny magnetic spot. The presence of a magnetic spot represent 1 bit and its absence represents 0 bit.
Hard disk are potentially very high capacity storage devices typically in the range of 20 megabyte to 1 gigabyte. Data are recorded on the tracks of a spinning disk surface and read from the surface by one or more read/write heads. There are two basic types of disk system.
1. Moving head
2. Fixed head
The moving head consist of one read/write head for each disk surface mounted on an axis and which can be moved in and out. In this system each read/write head moves horizontally across the surface of the disk. So that it is able to access each track individually. Information stored on the tracks which constitute a cylindrical shape through the disk pack are therefore accessed simultaneously.
In the fixed head system the axis are non-movable. A large number of read/write heads are distributed over the disk surfaces. One head for each track as a result no head movement is required and therefore information is accessed more quickly.
Optical Dist
An Optical disk can hold 4.7 gigabytes of data. It makes an immense amount of information available on a micro computer. Optical disks are having great impact on a storage technology these days. In optical disk technology a laser beam alters the surface of a plastic or metallic disk to represent data. To read the data a laser scans these areas and sends the data to a computer chip for conversion.
There are four kinds of optical disks available.
2. CD-R
3. Erasable Optical Disks
4. DVD
CD-ROM stands for Compact Disk Only memory. Unlike floppy disk and hard disk. Which use magnetic charge to represent 1s and 0s, optical disk use reflected light. On a CD-ROM disk 1s and 0s are represented by flat areas and bumpy areas (called pits) on its bottom surface. The CD-ROM disk is read by a laser that projects a tiny beam of light on these areas. The amount of reflected light determines whether they are represents a 1 or 0 Read-only means it cannot be written on or erased by the user.
CD-R stands for CD Recordable. CD-R disk can be written to once. After that they can be read many times without deterioration and can’t be written on or erased.
Erasable Optical Disks
Erasable Optical Disks are like CD-R except that they can be written to many times. There are two basic types of erasable optical disks. CD-RW which stands for compact disk rewriteable and MO which stands for magnetic optical.
DVD stands for digital versatile disk. DVD disks and disk drives and very similar to CD-ROM except that more data can be packed into same amount of space.DVD-ROM disks have a capacity of 4.7 gigabytes. They are being used for a variety of high-capacity needs such as recording and playing ful-length motion pictures advanced multimedia games and interactive encyclopedias


Micro Computers
Computers are the electronic devices that can follow instructions to accept input process that input and produce information. From capability point of view there are four types of computers as mentioned in the previous chapter.
1. Micro Computers
2. Mini Computers
3. Mainframe Computers
4. Super Computers
1. Micro Computers
The most widely used and fastest growing type of computer is the micro computer. There are two categories of micro computers desktop and portable. Desktop computers are small enough to fit along the side of a desk and yet are too big to carry around. Personal computer are the type of desktop. Portable computers are the micro computers that are small enough and light enough to move from one place to another. There are four categories of portable computers.
i. Laptops
ii. Notebooks
iii. Sub notebooks
iv. Personal Digital Assistants.
Components of Computer
The computer itself the hardware has many parts but each fall into one of four categories.
1. Processor
2. Memory
3. Input and Output Devices
4. Storage Devices.
Only first two categories will be discussed in this chapter, whereas next two categories will be studied in the subsequent chapter.
The CPU or Processor
The part of the computer that runs the program (executes processor) is known as the processor or central processing unit. The processor is like the brain of the computer the part that organizes and carries out the instructions that come from either user or software. The central processing unit has two components the control unit and the arithmetic logic unit.
Control Unit
The Control unit tells the rest of the computer system how to carry out a program’s instruction. It directs the movement of the electronic signals between teh memory which temporarily holds data, instruction and processed information and the arithmetic logic unit. It also direct the signal between the CPU and the input and output devices.
Arithmetic-logic Unit
The arithmetic logic unit usually called ALU performs two types of operations arithmetic and logical. The arithmetic operations are the fundamental math operations addition, substraction, multiplication and division. Logical operations consists of comparisons. i.e. two pieces of data are compared to see whether one is equal to (=), less than (<) or greater than (>) the other.
Memory (RAM)
Computer has two types of memory random access memory (RAM) and read only memory. (ROM) In this chapter only RAM will be studied whereas ROM will be studied later. RAM also known as primary memory internal memory or main memory hold.
Data for processing
Instruction for processing the data that is the program
Information that is processed data waiting to be output and sent to secondary storage such as floppy disk in a disk drive.
One of the most important fact to know about memory is that part of its content is held only temporarily. In other words, it is stored only as long as computer is turned on. When the machine is turned off the contents immediately vanish.
The next important facts of know about memory is that its capacity varies in different computers

Class XI, INFORMATION TECHNOLOGY, "Classification of Computers"

Types of Computers 1. Analog Computers
Analog computers are used to process continuous data. Analog computers represent variables by physical quantities. Thus any computer which solve problem by translating physical conditions such as flow, temperature, pressure, angular position or voltage into related mechanical or electrical related circuits as an analog for the physical phenomenon being investigated in general it is a computer which uses an analog quantity and produces analog values as output. Thus an analog computer measures continuously. Analog computers are very much speedy. They produce their results very fast. But their results are approximately correct. All the analog computers are special purpose computers.
2. Digital Computers
Digital computer represents physical quantities with the help of digits or numbers. These numbers are used to perform Arithmetic calculations and also make logical decision to reach a conclusion, depending on, the data they receive from the user.
3. Hybrid Computers
Various specifically designed computers are with both digital and analog characteristics combining the advantages of analog and digital computers when working as a system. Hybrid computers are being used extensively in process control system where it is necessary to have a close representation with the physical world.
The hybrid system provides the good precision that can be attained with analog computers and the greater control that is possible with digital computers, plus the ability to accept the input data in either form.
Classification of Computers According to Size
1. Super Computers
Large scientific and research laboratories as well as the government organizations have extra ordinary demand for processing data which required tremendous processing speed, memory and other services which may not be provided with any other category to meet their needs. Therefore very large computers used are called Super Computers. These computers are extremely expensive and the speed is measured in billions of instructions per seconds.
2. Main Frame Computers
The most expensive, largest and the most quickest or speedy computer are called mainframe computers. These computers are used in large companies, factories, organizations etc. the mainframe computers are the most expensive computers, they cost more than 20 million rupees. In this computers 150 users are able to work on one C.P.U. The mainframes are able to process 1 to 8 bits at a time. They have several hundreds of megabytes of primary storage and operate at a speed measured in nano second.
3. Mini Computers
Mini computers are smaller than mainframes, both in size and other facilities such as speed, storage capacity and other services. They are versatile that they can be fitted where ever they are needed. Their speeds are rated between one and fifty million instructions per second (MIPS). They have primary storage in hundred to three hundred megabytes range with direct access storage device.
4. Micro Computers
These are the smallest range of computers. They were introduced in the early 70’s having less storing space and processing speed. Micro computers of todays are equivalent to the mini computers of yesterday in terms of performing and processing. They are also called “computer of a chip” because its entire circuitry is contained in one tiny chip. The micro computers have a wide range of applications including uses as portable computer that can be plugged into any wall.
5. Laptop Computers
The smallest computer in size has been developed. This type of small computers look like an office brief case and called “LAPTOP” computer. The laptops are also termed as “PORTABLE COMPUTERS.” Due to the small size and light weight, they become popular among the computer users. The businessmen found laptop very useful, during traveling and when they are far away frm their desktop computers. A typical laptop computer has all the facilities available in microcomputer. The smallest laptops are called “PALMTOP

Class XI, INFORMATION TECHNOLOGY, "History of Computers"

History of Computers
At the early age people used pebbles, stones, sticks, scratches, symbols and finger tips to count, which were later replaced by numbers.
The history of computing is divided into three ages during which man invented and improved different types of calculating machines. These ages are,
  • Dark age – 300 BC to 1890
  • Middle age – 1890 AD to 1944
  • Modern age – since 1944 AD
Dark Age (3000 BC to 1890 AD
About 3000 years BC, Chinese developed the first calculating machine named Abacus or Soroban.
Abacus consists of a rectangular wooden frame having rods which carry round beads. Counting is done by shifting the beads from one side to another.
In 1632 AD William Oughtred, an English mathematician developed a slide rule. This device consists of two movable rules placed side by side on which number were marked.
Blasé Pascal (1623-1662), a French developed the first mechanical calculating machine in 1642. This machine consists of gears, wheels and dials. It was capable of adding and subtracting operations.
In 1671, a German, Gottfried Von Leibnitz (1646-1716) improved Pascal’s calculator to make it capable of performing all maths operations.
In 1801, a French, Joseph Marie Jacquard developed the first punch card machine.
Charles Babbage (1792-1871) an English mathematician also called Father of modern computer. As he gave the true concept of computer at Cambridge University, he developed Babbage Difference Engine in 1823 and Babbage Analytical Engine in 1833.
Lady Ada Augusta an assistant of Babbage is called the first programmer.
Middle Age (1890 AD TO 1944 AD)
In 1880s Herman Hollerith an American developed a machine which used punch card system. The machine could sense and punch holes, recognize the number and make required calculations. This machine was first used in 1890s by American Census Bureau.
In 1937, Professor Howard Aiken build the first electro-mechanical computer Mark-1, by trying to combine Babbage’s theory and Hollerith’s punching technologies. He completed his project in 1944 with the help of IBM Engineers.
Mark 1 could multiply two, twenty digit numbers in 5 seconds and made a lot of noise. It had a shape like a monster about 50 feet long, 8 feet high, having wiring of length equal to distance from Lahore to Gilgit or Karachi to Bahawalpur (800km) and had thousand ends of electro-magnetic relays.
ABC a special purpose computer was developed in 1938 by Dr. John Vincent Atanasoff and Clifford Berry at Iowa State College, USA.
Modern Ages (Since 1944 AD)
In 1945, Dr. John Von Neuman suggested the concept of Automatic Data Processing (ADP) according to the stored program and data. ENIAC
Electronic Numerical Integrator And Calculator (ENIAC) was the first electronic computer made in 1946 by John Presper Eckert and John Williams Mauchly, at the University of Pennsylvania, USA. This was based on decimal number system and it has no memory.
It could perform 5000 additions or 350 multiplications in one second. It contained 18000 vacuum tubes, 70,000 resistors, 10,000 capacitors and 60,000 switches and occupied a two room car garage. It consumed 150 kW of power. It weighed 27 tons.
Electronic Delay Storage Automatic Computer (EDSAC) was first computer based on stored program concept. It was completed by Mourice Wilkes at Cambridge University in 1949.
Electronic Discrete Variable Automatic Computer (EDVAC) was built by John Williams Mauchly, John Presper Eckert at Moore School, Pennsylvania in 1951.
UNIVersal Automatic Computer (UNIVAC) was the first commercially used computer made by John Presper Eckert and John Williams Mauchly in June 14, 1951.
Generations of Computer
First Generation of Computer (1946-1959)
Main Features
  • Major Innovation – Vacuum Tubes
  • Main Memory – Punched Cards
  • Input Output Devices – Punched cards and papers
  • Languages – Low level machine language
  • Operating System – No operating system, human operators to set
  • switches
  • Size – Main frame for example ENIAC, EDVAC, UNIVAC
The duration lasted from 1946-1959 was based on vacuum tubes. These vacuum tubes were about the size of 100 watt light bulb and used as the internal computer component. However because thousands of such bulbs were used, the computers were very large and generate a large amount of heat, causing many problems in temperature regulation and climate control.
In this generation input and out put device (punched card) that was used fro data storing purpose were very slow. The computers were operating manually and the language used was a low level machine language (symbolic language) with binary code that required a high programming skill. ENIAC, EDVAC, UNIVAC and Mark-1 were some of the major inventions of this generation.
Advantages of First Generation
1. Vacuum tubes were used as electronic component.
2. Electronic digital computers were developed for the first time.
3. These computers were the fastest calculating devices of their time.
4. Computations were performed in millisecond.
Disadvantages of First Generation
1. Too large in size.
2. They were unreliable.
3. Induce a large amount of heat due to the vacuum tubes.
5. Not portable.
6. Limited commercial use.
Second Generation of Computers (1959-1964)
Main Features
  • Major Innovation – Transistors as main component.
  • Main Memory – RAM and ROM.
  • External Storage – Magnetic tapes and Magnetic Disk.
  • Input Output Devices – Magnetic tapes and Magnetic Disk.
  • Languages – Assembly language, some high level languages for Example BASIC, COBOL, FORTRAN.
  • Operating System – Human handles punched card.
  • Size – Main frame for example IBM-1401, NCR-300, IBM-600 etc.
The period of this generation is from 1959 to 1964. During this period transistor were used for internal logic circuits of computers. These computers could execute 200000 instructions per second. The input/output devices became much faster by the use of magnetic table. During this period the low level programing language were used however the high level programming languages such as FORTRAN and COBOL were also used. The problem of heat maintenance was solved and size of computer reduced, while speed and reliability were increased. Many companies manufactured second generation computers and many of those for business applications. The most popular second generation computer was IBM-1401, introduced in 1960, while the following computers were used by many business organizations. IBM-1400 series, IBM-1600 series, UNIVAC-III, NCR-300 etc.
Advantages of Second Generation
1. Smaller in size as compares to 1st generation.
2. Much more reliable.
3. Less heat generated.
4. Computation was performing in micro second.
5. Less hardware and maintenance problem.
6. Could be used for commercial use.
Disadvantages of Second Generation
1. Very costly for commercial use.
2. It still required frequent maintenance.
3. Frequent cooling also required.
Third Generation of Computers (1965-1970)
Main Features
  • Major Innovation – Integrated circuit (ICs) as basic electronic component.
  • Main Memory – PROM and DRAM.
  • External Storage – Improve disk (Floppy Disk)
  • Input and Output Devices – Keyboard for input, monitor for output.
  • Languages – More high level languages.
  • Operating System – Complete operating systems were introduced.
  • Size – Mini, for example: IBM SYSTEM / 360, ICH-360, HONEY WELL-316 etc.
In this generation the integrated circuits (IC) were used. Integrated circuits contain many electronic components on a single chip. The disk oriented systems wee made at the end of this generation. The size of computer became very small with better performance and reliability. High level programming languages were extensively used. In 1969 the first microprocessor chip INTEL 4004 was developed but it was used only in calculators. The faster input/output devices made possible multi-processing and multi programming. Where by a number of input terminals could be run virtually at the same time on a single centrally located computer. The famous computer were IBM-360, IBM-370, UNIVAC 9000 series etc.
Advantages of Third Generation
1. Smaller in size as compared to second generation.
2. More reliable.
3. Portable
4. Less electricity consumption.
5. Heat generation was rare.
6. General purpose computer.
Disadvantages of Third Generation
1. Air conditioning was required in many cases due to ICs.
2. Very advance technology was required to make the ICs.
Fourth Generation of Computers (1971-1981)
Main Features
  • Major Innovation – LSIC and VLSIC (Micro Processor)
  • Main Memory – EPROM and SRAM.
  • External Storage – Floppy Disk and Hard Disk.
  • Input and Output Devices – Monitor for output.
  • Languages – Languages and application softwares.
  • Operating System – MS-DOS and PC-DOS
  • Size – Micro computer e.g. IBM-PC, Apple Macintosh etc.
The Integrated circuits were more developed and called Small scale integration (SSI), after some time the SSI were more developed and termed as Large scale integration (LSI). There was a great versatility of input/output devices. In 1971, a powerful microprocessor chip INTEL 8008 was introduced. The first microprocessor which is used in personal computers (PC) was INTEL 8080. The 8 inch floppy disk was also introduced in 1971, while hard disk was introduced in 1973. The 5.25 floppy disk was first time used in 1978. The optical disk was developed in 1980. First portable computer “Osborne I” was marketed in 1981. IBM-3033, IBM-370, IBM system 34, IBM system 36, Cray-I, CP/M etc were introduced in this generation.
Advantages of Fourth Generation
1. Smaller in size and much reliable.
2. No cooling system required in many cases.
3. Much faster computation.
4. Portable and cheap.
5. The heat generated was negligible.
6. Totally general purpose computer.
Disadvantages of Fourth Generation
1. Very advanced technology was required to fabricate to the ICs.
Fifth Generation (1981-Onward)
Main Features
  • Major Innovations – ULSIC (Ultra large scale integrated circuit)
  • Main Memory – EEPROM, SIMM and DIMM.
  • External Storage – Modified magnetic and Optical disks.
  • Input/output Devices – Keyboard, Pointing Device, Scanner as input and Monitor as main output.
  • Languages – AI (Artificial Intelligence) Expert systems.
  • Operating System – GUI based e.g. Windows 95, Windows NT.
  • Size – Very small in size example: Laptop, Note book, Digital Diary, Palm top and Pocket PC.
This generation is started from 1981 and still continued, new technologies are adopted to fabricate IC chips, such as electron beam, X-rays or laser rays. The Very Large Scale Integration
(VLSI) was developed, so the computer became much smaller than ever before. New memory storage device like bubble memory, optical or memory are being designed. the new computer will be controlled by using human voice and will work by giving command in our own language. Future computer will in some way to be intelligent and capable of making decision.
Advantages of Fifth Generation
1. Very large storage capacity.
2. Long bit processor builds.
3. Artificial Intelligence Language developed


We have truly entered the information age. It is nothing but information technology and its rapidly growing use that has converted the world into a global village. The emergence of global village, with the rapid spread of information technology, is having its tremendous impact on every aspect of life. Information Technology has completely revolutionized business, education, military strategies and important of all, our way of thinking.
Definition of Information Technology
The concept and the term information technology is so broad that no precise and comprehensive definition, encompassing all the aspects of IT, can be given. Because information technology is set of various diversified and multidimensional technologies. Despite that we may try to define
IT is a set of technologies that merge computing with high speed communication communication links carrying data, sound and videos.
Examples of information technology include personal computers, of course, but also new forms of telephones, televisions and various handheld devices, such as personal digital assistants.
It should be noted that there are two parts of this definition, the computers and communications.
A computer is a programmable, multi-use machine that accepts data, the raw facts and figure, and process or manipulates it into information that we can use, such as summaries totals or reports. Its purpose is to speed up problem solving and to increase productivity.
Communication technology also called telecommunication technology consists of electromagnetic devices and systems communicating over long distances. The principle examples are telephone, radio broadcast, television and cable TV. More recently, there has been an addition of communication among computers, when people tell you that they “went online” with the Internet. To be online means using a computer or other device connected through a voice or data network, to access information and services from another computer or information device.
Now the students may be convinced that there a use of computer is not information technology, rather it is a set of technologies. Computer is just a part of it, through the most important and amazing.
Importance of Computers
The computer is truly an amazing machine. Few tools, other than computers, can help you perform so many different tasks in so many areas of life. That’s why computers have become so fundamental to modern society that without them our society would be a primitive one. They are such flexible tools that most people in the business community use them every day. Office workers use them to write letters, keep employee rosters, create budgets communicate with coworkers, find information, manage projects and so on. Many business people even when they are away from the office, for instance, salespeople use computers to manage accounts and make presentation.
Computers are also vital accounting departments. For organizing and manipulating large sets of numbers, which accounting departments do daily, computers are now considered essential. Even small business, which can comprise just a single person can afford to set up sophisticated accounting systems using a personal computer and affordable accounting and financial packages.
Even if you do work in a business computers effect you every day. Any time you go to the bank call information for a phone number or buy something out of a catalog, you are benefiting from the power and speed of computers. Even when you buy groceries and gasoline, you may be interacting with computers.
Capabilities of Computer
Besides being a multi-use device a computer has a number of remarkable capabilities namely very fast speed, accuracy, consistency, reliability and sufficiently large memory.
A computer can perform various activities by executing programs at a very fast speed. For example it can perform tedious calculations immediately. While a man would take very large time to perform the same job.
Along side speed the tasks performed by a computer are almost accurate. However you may some times come across program logic error, a procedural error or an error in data. But these error are not of computer rather these are human error, i.e. it is the man who makes these error while interacting with computer.
During performing a tedious task a man can get tired and he may want to change the nature of the job he is performing or at least he may to change the way he perform his task. But as computer works according to a preprogrammed way. i.e. it has to follow the instruction given to it in the form of a program computer has to perform required tasks with consistency.
As mentioned above, the computers have the capabilities to perform a required task in accordance with the preprogrammed instructions with a great speed, accuracy and consistency. Hence the job performed by a computer is highly reliable.
Memory Capability
Man has very limited memory and recalling ability, whereas computer not only have a great capability of storing data in its memory but can also recall this huge amount of data instantly. For example, insurance companies use mainframe computers to process information about millions of policy holders. Obviously no man, even the genius people, can store such huge amount of data in his memory. Even if he could it would be impossible for him to recall required information instantly. While computer can do this job easily.
Uses of Computers
Can you think of a field where you can perform your job efficiently and productively, without the use of computer? Certainly you can’t. No matter what career you choose the use of computers will affect you life for this wonderful machine has encompassed almost all the aspects of human life. Some of the fields where in computers are being used extensively are:
Information Management
As computers are excellent tools for managing large quantities of information, they are being extensively used by various organizations for various purposes like airline reservations, student registration, billing and countless others.
Computer specially combined with tools of telecommunications has become the most effective tool of communication. All the organizations need to communicate with each other, besides communicating with the various departments of the same organization in order to run their day to day business efficiently. The use of computers has facilited this task. Moreover now one can instantly communicate with the people all around the world through internet.
Education and research
Perhaps the most fruitful and productive use of computers has been in the fields of education, scientific and engineering research. The use of computers has converted education into edutainment. Engineers and scientists are utilizing computers as a tool of experimentation design and development. In this respect computerized design (CAD) provides a sophisticated array of tools.
Business and E-Commerce
The emergence of the concept of e-commerce is the result of wide spread use of computers in business. This has motivated almost all the business community to redefine the customer-salesperson relationship. Now you need not to go to super market for shopping for you may place you orders electronically. E-banking and E-commerce has reduce the costs of distribution of commodities and services tremendous.
The idea of e-government i.e. providing government service electronically using computers is under its way. The NADRA is an example of utilizing computers for this purpose. Besides the use of computers in the field of health and medicine, agriculture and industries has not only revolutionized these fields but has reduced the cost of production and distribution of goods and services resulting in an over all increase in the standard of living of a common man.
The Impact of Information Technology
The rapid advancement in the field of computers and information technology is having its consequences not only on the organizations but not individuals too. In this connection the most important impact of computers and information technology is undoubtedly the emergence of globalization. Computer based communication is turning the world into a global village. We can communicate electronically using the tools of information technology with the people on the other side of the world as easily as we might have a coversation with a neighbor. Besides the process of globalization information technology is influencing the society in the following ways.
Better Planning and Decision Making
Computer based information systems are facilitating decision making through better planning. As the information technology has improved the communication to the unbelievable extent, the multinational organizations are pooling their information for the better future forecast and planning.
Better Control of Resources
It is essential particularly in business organizations to check whether the planned goals and objectives are being achieved or not. In this respect computer system due to their power and reliability for accuracy can be utilized to measure actual performance levels and to compare these levels with panned standards. Not only this rapid communication of information through the use of information technology provides the business firms with an opportunity to compare its operational efficiency with that of other firms.
Greater Efficiency of Operation
Not to speak of IT and computer experts and professionals even a lay man in the street can realize that the use of computers along with other tools of information technology has improved the efficiency of operation particularly in industrial proces

Class XI, CHEMISTRY, "Chemical Kinetics"

Chemical Kinetics Introduction
The branch of physical chemistry which deals with the speed or rate at which a reaction occurs is called chemical kinetics.
The study of chemical kinetics, therefore includes the rate of a chemical reaction and also the rate of chemical reaction and also the factors which influence its rate.
Slow and Fast Reaction
Those reactions for which short time is required to convert a reactant into product are called fast reaction but if more time is required for the formation of a product then the reactions are called slow reactions.
Usually ionic reactions which involve oppositely charged ions in aqueous medium are very fast. For example, reaction between aqueous solution of NaCl and AgNO3 gives white precipitates of AgCl instantaneously.
AgNO3 + NaCl —-> AgCl + NaNO3
Such reactions are very fast and these are completed in fractions of seconds.
But those reactions which involve covalent molecules take place very slowly. For example, conversion of SO2 into SO3
2 SO2 + O2 —-> 2 SO3
It is a slow reaction and required more time for the formation of a product.
Rate Or Velocity of a Reaction

It is the change in concentration of a reactant or product per unit time.
Mathematically it is represented as
Rate of reaction = Change in concentration of reactant or product / Time taken for the change
The determination of the rate of a reaction is not so simple because the rate of a given reaction is never uniform. It falls off gradually with time as the reactants are used up. Hence we can not get the velocity or rate of reaction simply by dividing the amount of substance transformed by the time taken for such transformation. For this reason we take a very small interval of time “dt” during which it is assumed that velocity of reaction remains constant. If “dx” is the amount of substance transformed during that small interval of time “dt” then the velocity of reaction is expressed as
Velocity of a reaction = dx / dt
Thus with the velocity of a chemical reaction we mean the velocity at the given moment or given instant.
The Rate Constant

The proportionality constant present in the rate equation is called rate constant.
According to law of mass action we know that the rate of chemical reaction is directly proportional to the molar concentration of the reactants. For example
R —-> P
The rate of reaction ∞ [R]
dx / dt = K [R]
Where K is known as rate constant.
Specific Rate Constant
When the concentration and temperature both are specified, the rate constant is known as specific rate constant.
When the concentration of each reactant is 1 mole per dm3 at given temperature, the specific rate constant numerically equals to the velocity of the reaction.
dx / dt = V = K [R]
K = V / [R]
When R = 1 mole/dm3
K = V
But when different reactant are reacting with different number of moles then the value of K may be calculated as
2 SO2 + O2 —-> 2 SO3
= dx / dt = K [SO2]2 [O2]
K = V / [SO2]2 [O2]
Determination of Rate of Reaction
There are two method for the determination of rate of a chemical reaction.
1. Physical Method
When the rate of a chemical reaction is determined by using physical properties such as colour change, volume change, state change the method known as physical method.
2. Chemical Method
In the method the change in concentration of reactant or product is noted and with the help of this change rate of reaction is determined e.g.,
For the reaction R —-> P
Velocity of reaction = – d[R] / dt = + d[P] / dt
The negative sign indicates a decrease in concentration of the reactant while positive sign indicates an increase in the concentration of product.
Ionization is thus a reversible process. To this process, the law of mass action can be applied as
K(C) = [Na+] [Cl-] / [NaCl]
3. The number of positive and negative charges on the ions must be equal so that the solution as a whole remains neutral.
4. The degree of ionization of an electrolyte depends upon (a) the nature of electrolyte, (b) dilution of the solution (c) the temperature
5. When an electric current passes through the solution of an electrolyte the positive ions i.e., the cations move towards the cathode and the anions move towards the anode. This movement of ions is responsible for the conductance of electric current through the solution.
6. The electrical conductivity of the solution of an electrolyte depends upon the number of ions present in the solution. On reaching the electrodes, the ions lose their charge and change into neutral atoms or molecules by the gain or loss of electrons.
Applications of Arrhenius Theory
This theory explain many peculiarities in the behaviour of electrolytic solutions.
For example, the elevation in boiling point of 1 molal solution of glucose is 0.52ºC while this elevation in 1 molal solution of NaCl is 1.04ºC. This difference in elevation of boiling point can be explained on the basis of Arrhenius theory.
In one molal solution of glucose the number of (molecules) particles are 6.02 x 10(23) per dm3 of solution while in 1 molal solution of NaCl 6.02 x 10(23) ions of Na+ and 6.02 x 10(23) ions of Cl- are present because NaCl is an ionic compound. Since the number of particle are double in NaCl solution, therefore the elevation in boiling point is also double than the solution of glucose.
Similarly the other collegative properties such as lowering in vapour pressure, depression in freezing point and osmosis are explained on the basis of this theory.
Collegative properties are those properties which depends upon the number of particles.
Conductance of Electric Current Through Solutions
The ability of a solution to conduct electric current depends upon the ions present in the solution. The conductance of a solution is increased when
1. The solution is diluted
2. The degree of dissociation of the electrolyte is high
3. The temperature of the solution is high
4. The velocity of the ions is high
But in a concentrated solution, the number of ions per unit volume of solution increases and the distance between ions decreases causing strong interionic attraction. As a result, migration of ions becomes more difficult and the conductance decreases with increase in concentration. As the conductance is related with the movement of ions, so conductance increase with the increase of absolute velocity of ions in the solution.
The conductance of an electrolyte also depends upon the degree of ionization. The degree of ionization is denoted by α and calculated as
α = No. of dissociated molecules / Total molecules dissovled
A chemical substance which can conduct electric current in molten form or in its aqueous solution with a chemical change is called electrolyte.
The movement of anions and cations towards their respective electrodes with all accompanying chemical changes in an electrolytic solution under the influence of electric current is known as electrolysis.
To explain the phenomenon of electrolysis consider the example of CuCl2 solution. the ionization of CuCl2 in the solution may be represented as
CuCl2 <—-> Cu+2 + 2 Cl-
When electric current is passed through this solution, the movement of these ions begins to take place Cu+2 ions migrate towards cathode and Cl- ions towards anode. At cathode Cu+2 ions are discharged as copper atoms by the gain of electrons (reduction)
Cu+2 + 2 e- —-> Cu(M) …….. Reduction at Cathode
At anode Cl- ions are discharged as Cl2 by the loss of electrons (oxidation)
2 Cl- – 2 e- —-> Cl2(g0 …… Oxidation at Anode
The overall reaction of the electrolysis may be written as
Cu+2 + 2 e- —-> Cu(M)
2 Cl- – 2 e- —-> Cl2(g)
Cu+2 + 2 Cl- —-> Cu(M) + Cl2(g)
CuCl2 —-> Cu(M) + Cl2(g)
When all the ions present in the solution have been changed to neutral particles, the flow of current is stopped