Unit-1: introduction to computers

Being a modern-day kid you must have used, seen, or read about computers. This is because they are an integral part of our everyday existence. Be it school, banks, shops, railway stations, hospital or your own home, computers are present everywhere, making our work easier and faster for us. As they are such integral parts of our lives, we must know what they are and how they function. Let us start with defining the term computer formally.

The literal meaning of computer is a device that can calculate. However, modern computers can do a lot more than calculate. Computer is an electronic device that receives input, stores or processes the input as per user instructions and provides output in desired format.

Input-Process-Output Model

Computer input is called data and the output obtained after processing it, based on user’s instructions is called information. Raw facts and figures which can be processed using arithmetic and logical operations to obtain information are called data.


The processes that can be applied to data are of two types −

  • Arithmetic operations − Examples include calculations like addition, subtraction, differentials, square root, etc.
  • Logical operations − Examples include comparison operations like greater than, less than, equal to, opposite, etc.

The corresponding figure for an actual computer looks something like this −

Block Diagram

The basic parts of a computer are as follows −

  • Input Unit − Devices like keyboard and mouse that are used to input data and instructions to the computer are called input unit.
  • Output Unit − Devices like printer and visual display unit that are used to provide information to the user in desired format are called output unit.
  • Control Unit − As the name suggests, this unit controls all the functions of the computer. All devices or parts of computer interact through the control unit.
  • Arithmetic Logic Unit − This is the brain of the computer where all arithmetic operations and logical operations take place.
  • Memory − All input data, instructions and data interim to the processes are stored in the memory. Memory is of two types – primary memory and secondary memory. Primary memory resides within the CPU whereas secondary memory is external to it.

Control unit, arithmetic logic unit and memory are together called the central processing unit or CPU. Computer devices like keyboard, mouse, printer, etc. that we can see and touch are the hardwarecomponents of a computer. The set of instructions or programs that make the computer function using these hardware parts are called software. We cannot see or touch software. Both hardware and software are necessary for working of a computer.

Characteristics of Computer

To understand why computers are such an important part of our lives, let us look at some of its characteristics −

  • Speed − Typically, a computer can carry out 3-4 million instructions per second.
  • Accuracy − Computers exhibit a very high degree of accuracy. Errors that may occur are usually due to inaccurate data, wrong instructions or bug in chips – all human errors.
  • Reliability − Computers can carry out same type of work repeatedly without throwing up errors due to tiredness or boredom, which are very common among humans.
  • Versatility − Computers can carry out a wide range of work from data entry and ticket booking to complex mathematical calculations and continuous astronomical observations. If you can input the necessary data with correct instructions, computer will do the processing.
  • Storage Capacity − Computers can store a very large amount of data at a fraction of cost of traditional storage of files. Also, data is safe from normal wear and tear associated with paper.

Advantages of Using Computer

Now that we know the characteristics of computers, we can see the advantages that computers offer−

  • Computers can do the same task repetitively with same accuracy.
  • Computers do not get tired or bored.
  • Computers can take up routine tasks while releasing human resource for more intelligent functions.

Disadvantages of Using Computer

Despite so many advantages, computers have some disadvantages of their own −

  • Computers have no intelligence; they follow the instructions blindly without considering the outcome.
  • Regular electric supply is necessary to make computers work, which could prove difficult everywhere especially in developing nations.


Starting a computer or a computer-embedded device is called booting. Booting takes place in two steps −

  • Switching on power supply
  • Loading operating system into computer’s main memory
  • Keeping all applications in a state of readiness in case needed by the user

The first program or set of instructions that run when the computer is switched on is called BIOS or Basic Input Output System. BIOS is a firmware, i.e. a piece of software permanently programmed into the hardware.

If a system is already running but needs to be restarted, it is called rebooting. Rebooting may be required if a software or hardware has been installed or system is unusually slow.

There are two types of booting −

  • Cold Booting − When the system is started by switching on the power supply it is called cold booting. The next step in cold booting is loading of BIOS.
  • Warm Booting − When the system is already running and needs to be restarted or rebooted, it is called warm booting. Warm booting is faster than cold booting because BIOS is not reloaded.

Block diagram of a computer gives you the pictorial representation of a computer that how it works inside. Or you can say that, in computer’s block diagram, we will see how computer works from feeding the data to getting the result.

Here is the block diagram of a computer system:

block diagram of computer

In the above diagram, both control (control unit or CU) and arithmetic & logic unit (ALU)combinely called as Central processing unit(CPU)

Let’s describe about all the parts as included in the above diagram one by one.

The Processor Unit (CPU)

It is the brain of the computer system.

All major calculation and comparisons are made inside the CPU and it is also responsible for activation and controlling the operation of other unit.

This unit consists of two major components, that are arithmetic logic unit (ALU) and control unit (CU).

Arithmetic Logic Unit (ALU)

Here arithmetic logic unit performs all arithmetic operations such as addition, subtraction, multiplication and division. It also uses logic operation for comparison.

Control Unit (CU)

And the control unit of a CPU controls the entire operation of the computer. It also controls all devices such as memory, input/output devices connected to the CPU.

CU fetches instructions from memory, decodes the instruction, interprets the instruction to know what the task are to be performed and sends suitable control signals to the other components to perform for the necessary steps to executes the instruction.

Input/Output Unit

The input/output unit consists of devices used to transmit information between the external world and computer memory.

The information fed through the input unit is stored in computer’s memory for processing and the final result stored in memory can be recorded or display on the output medium.

Memory Unit

Memory unit is an essential component of a digital computer. It is where all data intermediate and find results are stored.

The data read from the main storage or an input unit are transferred to the computer’s memorywhere they are available for processing.

This memory unit is used to hold the instructions to be executed and data to be processes.

Disk Storage Unit

Data and instruction enters into a computer system through input device have to stored inside the computer before actual processing start.

Two types of storage unit are primary and secondary storage unit.

Primary Storage Unit

Primary memory has direct link with input unit and output unit. It stores the input data, calculation result.

Secondary Storage Unit

The primary storage is not able to store data permanently for future use. So some other types of storage technology is required to store the data permanently for long time, it is called secondary or auxiliary storage.

Computers can be broadly classified by their speed and computing power.S.No.TypeSpecifications1PC (Personal Computer)It is a single user computer system having moderately powerful microprocessor2WorkstationIt is also a single user computer system, similar to personal computer however has a more powerful microprocessor.3Mini ComputerIt is a multi-user computer system, capable of supporting hundreds of users simultaneously.4Main FrameIt is a multi-user computer system, capable of supporting hundreds of users simultaneously. Software technology is different from minicomputer.5SupercomputerIt is an extremely fast computer, which can execute hundreds of millions of instructions per second.

PC (Personal Computer)

Personal Computer

A PC can be defined as a small, relatively inexpensive computer designed for an individual user. PCs are based on the microprocessor technology that enables manufacturers to put an entire CPU on one chip. Businesses use personal computers for word processing, accounting, desktop publishing, and for running spreadsheet and database management applications. At home, the most popular use for personal computers is playing games and surfing the Internet.

Although personal computers are designed as single-user systems, these systems are normally linked together to form a network. In terms of power, now-a-days high-end models of the Macintosh and PC offer the same computing power and graphics capability as low-end workstations by Sun Microsystems, Hewlett-Packard, and Dell.


Work Stations

Workstation is a computer used for engineering applications (CAD/CAM), desktop publishing, software development, and other such types of applications which require a moderate amount of computing power and relatively high quality graphics capabilities.

Workstations generally come with a large, high-resolution graphics screen, large amount of RAM, inbuilt network support, and a graphical user interface. Most workstations also have mass storage device such as a disk drive, but a special type of workstation, called diskless workstation, comes without a disk drive.

Common operating systems for workstations are UNIX and Windows NT. Like PC, workstations are also single-user computers like PC but are typically linked together to form a local-area network, although they can also be used as stand-alone systems.


It is a midsize multi-processing system capable of supporting up to 250 users simultaneously.

Mini Computer


Mainframe is very large in size and is an expensive computer capable of supporting hundreds or even thousands of users simultaneously. Mainframe executes many programs concurrently and supports many simultaneous execution of programs.

Main Frame


Supercomputers are one of the fastest computers currently available. Supercomputers are very expensive and are employed for specialized applications that require immense amount of mathematical calculations (number crunching).

Super Computer

For example, weather forecasting, scientific simulations, (animated) graphics, fluid dynamic calculations, nuclear energy research, electronic design, and analysis of geological data (e.g. in petrochemical prospecting).