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Computer is an advanced electronic device that takes raw data as input from the user and processes these data under the control of set of instructions (called program) and gives the result (output) and saves output for the future use. It can process both numerical and non-numerical (arithmetic and logical) calculations.

a. A computer has four functions:
  • Accept data                       Input
  • Processes data                 Processing
  • Produces information      Output
  • Stores results                    Storage
b. Parts of Computer
  • CPU
  • Keyboard
  • Mouse
  • Monitor
  • Printer
  • UPS
  • Speakers

Input Data: Input is the raw information entered into a computer from the input devices. It is the collection of letters, numbers, images etc.

Process: Process is the operation of data as per given instruction. It is totally internal process of the computer system.

Output: Output is the processed data given by computer after data processing. Output is also called as Result. We can save these results in the storage devices for the future use.


It was in the year 1823 that a famous English man Charles Babbage built a mechanical machine to do complex mathematical calculations. Later he developed a general-purpose calculating machine called analytical engine. However his device remained unfinished. But for his pioneering work he is called the father of computer. Today’s computers overcome 5 long generations which are named  1st generation, 2nd generation, 3rd generation, 4th generation & 5th generation .


The computers in first generation were very big in size, vacuum tubes and valves were used at that time. Computers were slow and not suitable for longer time process. When we use it for a longer period of time it gave erroneous result due to the heat effect. ENIAC: It was the first electronic computer built in 1946 at University of Pennsylvania, USA by John Eckert and John Mauchy. It was named Electronic Numerical Integrator and Calculator (ENIAC).


In this generation transistor technology were developed which replaces vacuum tubes and valves. So the computer becomes compact and reliable for longer time process.


In third generation Integrated Circuit (IC) technology were developed. Particularly SSI and MSI technology. IC means more one circuit packed in a single chip. SSI [Small Scale Integration] : Here maximum 10 circuits can be packed in a same chip MSI [Medium Scale Integration] : Here 10 to 100 circuits are packed in same chip.


The present day computers that you see today are the fourth generation computers that started around 1975. It uses large scale Integrated Circuits (LSIC) built on a single silicon chip called microprocessors. Due to the development of microprocessor it is possible to place computer’s central processing unit (CPU) on single chip. These computers are called microcomputers. Later very large scale Integrated Circuits (VLSIC) replaced LSICs. LSI [Large Scale Integration] : It consists of 100-1000 circuits in a single chip. VLSI [Very Large Scale Integration] : Here more than 1000 circuits are packed in a single chip. Super computer is developed in this generation. It uses VLSI technology.


The AI technology [Artificial Intelligence] falls in this generation. It is developed in only in two countries, USA and Japan. In this generation computers can think in some pre-defined situation, which was not possible up to fourth generation.

Computer can be generally classified by size power, although there can be considerable overlap. Following are descriptions of several different types of computer.

  • Micro computer
  • Mini Computer
  • Mainframe Computer
  • Super Computer

Micro Computer:

Personal Computers (PCs) are called microcomputers, are the most popular type of Computer in use today. Micro Computers are used as home computers by families, by business executives or by small business. The PC is a small-sized, relatively inexpensive computer designed for an individual user. Computers may be called ‘desktop’ computers, which stay on the desk, or ‘laptop’ computers, which are lightweight and portable. Organizations and individuals use PCs for a wide range of tasks, including word processing, accounting, desktop publishing, preparation and delivery of presentations, organization of spreadsheets and database management etc.

Mini Computer

Minicomputers are more powerful than microcomputers and this is designed to support more than one user at a time. It possesses large storage capacity and operates at a higher speed. The mini computer is used in multi-user system in which various users can work at the same time. This type of computer is generally used for processing large volume of data in an organization. They are also used as servers in Local Area Networks (LAN).

Mainframe Computer:

Mainframe computers are large-sized, powerful multi-user computers that can support concurrent programs. That means, they can perform different actions or ‘processes’ at the same time. Mainframe computers can be used by as many as hundreds or thousands of users at the same time. Large organizations may use a mainframe computer to execute large-scale processes such as processing the organization’s payroll. They are also used as controlling nodes in Wide Area Networks (WAN). Example of mainframes are DEC, ICL and IBM 3000 series

Super Computer:

They are the fastest and most expensive machines. They have high processing speed compared to other computers. They have also multiprocessing technique. One of the ways in which supercomputers are built is by interconnecting hundreds of microprocessors. Supercomputers are mainly being used for weather forecasting, biomedical research, remote sensing, aircraft design and other areas of science and technology. Examples of supercomputers are CRAY YMP, CRAY2, NEC SX-3, CRAY XMP and PARAM from India.

All of the components of a computer system can be summarized with the simple equations.

  • HARDWARE = All physical parts of the computer (or everything that we can touch) are known as Hardware.

  • SOFTWARE = The Programs of the computer that instructs the computer how to process the data and generate the required information are called Software. We can’t touch the programs/software.

  • PERSONNEL= Person, who operates computer.

HARDWARE HARDWARE = Internal Devices + Peripheral Devices
  1. CPU:

The brain of the Computer is called CPU or the processor. CPU is the main component of the Computer. It takes all major decisions, makes all sorts of calculations and directs different parts of the computer functions by activating and controlling the operations. It includes three major components.

  1. Control Unit (CU)
  2. Arithmetic and Logical Unit (ALU)
  3. Main memory

Control Unit controls the sequence of actions by the program and input / output operations. It is the nerve center of the CPU. The control unit co- ordinates the flow of data and instruction in a CPU.


The Arithmetic and Logical Unit (ALU) performs all types of arithmetic calculations such as addition, subtraction, multiplications and division and also it performs the logical and comparative analysis.


Memory is the place where we can store information. It is of two kinds.

  1. Primary Memory

Random Access Memory (RAM): This is the main memory of the CPU where programs (instructions) and data are stored while processing. The storage of data and instructions in the RAM is temporary. It disappears from RAM as soon as the power to the computer is switched off. The memories, which lose their content on failure of power supply, are known as volatile memories. So now we can say that RAM is volatile memory.

Read Only Memory (ROM): There is another memory in computer, which is called Read Only Memory (ROM). The storage of program and data in the ROM is permanent. The ROM stores some standard processing programs supplied by the manufacturers to operate the person­al computer. The ROM can only be read by the CPU but it cannot be changed.  ROM retains the data in it even in the absence of power and is thus non-volatile storage.

  1. Secondary Memory :

Secondary memory is a type of memory that can hold data, instruction and information for future use.


Peripherals devices in a computer system are classified as

  1. Input device
  2. Output device
  • Storage device
Input Device

Input device are required to feed data and instruction into the computer. In others words a user communicates with a computer system using input devices. Common input devices are the keyboard, mouse, scanner, microphone, digital camera, Joystick, touch Screen, Web camera, Bar Code Reader, Bluetooth, Graphics Tablets etc.

Output Device

Output device are those, which give out the information processed by the computer. In other words the computer communicates with the user help of an output device. Common output devices are Monitor, Printer, Projector, Speakers.

Storage Device

Storage Device also known as secondary memory. They can hold data, instruction and information for future use. Common Storage devices are Floppy Disc Drive (FDD), Hard Disc Drive (HDD), Compact Disc Read Only Memory (CD-ROM), Pen drive, Memory Card etc.


Software can be broadly classified into two categories

  • System Software
  • Application Software

System Software: System software is computer program that run a computer system itself or assist in running application programs. System software is hardware oriented.

For example- Operating system (MS Dos, UNIX, Windows 98, Windows XP, Windows Vista, Windows 7)

Application Software: Application software is a computer program that is user oriented. They are designed to accomplish specific user tasks such as helping to write letters, drawing, calculating, accounting, payroll Etc.

For example-
    Word processors (MS-Word, Word Perfect etc)

  • Spreadsheet (MS Excel, Lotus 123 etc.)

  • DBMS- Database Management System (MS Access, Oracle, SQL Server etc.)

  • Publishing (PageMaker, CorelDraw etc.)

  • Graphics Designing (Photoshop, Firework, AutoCAD, 3D Studio etc.)

  • Animation (Maya, Flash etc.

Central Processing Unit (CPU)- The processing device of the computer is the central processing Unit CPU. It is used to process the data inside the computer. It is also used to control the operations and functions of the computer. The CPU is like the brain of the computer.

Hidden parts of CPU:
  1. Microprocessor
  2. Motherboard
  3. SMPS (Switch Mode Power Supply)
  4. RAM (Random Access Memory)
  5. FDD (Floppy Disc Drive)
  6. HDD (Hard Disc Drive)
  7. CDD (Compact Disc Drive)
  8. Card : Internet Card, Ethernet Card
  9. IDE (Integrated Development Environment) cable.
  10. SATA (Serial Advance Technology Attachment) cable.

Keyboard- The keyboard is an input device like a typewriter. When you press a key on the keyboard, it will show on the monitor. The keyboard keys are used to type data and commands and enter them into the memory of the computer. Keyboards can have 101 to 105 keys.

TYPES OF KEYS ON THE KEYBOARD Alphabet Keys                     : A to Z
Number Keys                       : 0 to 9
Function Keys                     : F1, F2 ……………F12
Punctuation Keys               : .   ,   ;   ‘   :   “
Symbol Keys                         : !  @  #  $  %  ^  &  *  (  )  |  {  }  _  +  ?  \  /  < >
Text Editing Keys                : Insert, Delete, Home, End, Page Up, Page Down
Special Control Keys          : Enter, Shift, Alt, Ctrl, Tab, Caps Lock, Space bar, Back Space.
Direction of Cursor Key     : Up     , Down     , Left           , Right

Mouse- The mouse is also an input device. The mouse can have three buttons on it. By moving the mouse on the mouse pad, you can move the arrow pointer on the monitor. The mouse is also used to control the cursor on the monitor. A mouse is a pointing device that fits comfortably under the palm of your hand.

Monitor- The Monitor is an important output device. A monitor displays information in visual form, using text and graphics. The portion of the monitor that displays the information is called the screen. Like a television screen, a computer screen can show still or moving pictures.

There are two basic types of monitors: CRT (cathode ray tube) monitors and the newer LCD (liquid crystal display) monitors. Both types produce sharp images, but LCD monitors have the advantage of being much thinner and lighter.

Printer- The printer is another important output device. It prints the results or output on paper. Printers can be put into groups depending on their speed, print quality and how they print (technology used). There are Dot Matrix Printers, Ink Jet Printers and Laser Printers.

UNINTERRUPTIBLE POWER SUPPLY (UPS)- A UPS is a device that provides battery backup when the electrical power fails or drops to an unacceptable voltage level. If you are using the computer when the UPS notifies you of the power loss, you have time to save any data you are working on and exit gracefully before the secondary power source (the battery) runs out. When all power runs out, any data in your computer’s random access memory (RAM) is erased.

SPEAKERS- Speakers are used to play sound. They can be built into the system unit or connected with cables. Speakers allow you to listen to music and hear sound effects from your computer.

Windows is an operating system. This provides an interface between the user and the computer system (hardware). Windows is a GUI (Graphical User Interface) system. . It is the main master control program where all loading software’s are contained. When we install any software in our system, than it connects with the main Operating system. So, it is the main backbone program of a system.

There are many versions of Windows. They are:
  1. Windows 3.1
  2. Windows 95
  3. Windows NT.
  4. Windows 98
  5. Windows 2000
  6. Windows Me.
  7. Windows XP.
  8. Windows Vista.
  9. Windows 7
  • Desktop tools.
  • Start connecting Tools.
  • Accessories Connecting Tools.
  • Organization of Files & Folder.
  1. Desktop Tools: The main screen of your computer is called Desktop. There are small size pictures on the desktop screen which are called Icons. Icons are small pictures that represent files, folders, programs, and other items. Some icons are

    1. My Computer
    2. My Documents
  • Recycle bin
  1. Windows Media Player etc.

The long horizontal bar at the bottom of your screen is called taskbar.

  1. Start connecting Tools: The Start menu is the main gateway to your computer’s programs, folders, and settings. It’s called a menu because it provides a list of choices.
    Use the Start menu to do these common activities:

  • Start programs
  • Open commonly used folders
  • Search for files, folders, and programs
  • Adjust computer settings
  • Get help with the Windows operating system
  • Turn off the computer
  • Log off from Windows or switch to a different user account
  1. Accessories Connecting Tools.

It is a windows folder where communications, Address book, Notepad, Calculator, Paint, and Word pad, Internet Tools are connected.

  1. Organization of Files & Folder.

File is a collection of data or information that has a name. Almost all information stored in a computer must be a file.

FOLDER- A folder is a location where you can store your files. You can create any number of folders and even store folders inside other folders (subfolders).