What is Computer System?

Computer System

Computer is a useful machine. It is used in almost every sphere of life. We can play games, write letters, draw pictures, listen to music, store information, solve mathematical problems etc on a computer. It can work very fast and can do more jobs at the same time.


The physical parts of a computer that we can touch and feel are called Hardware. As we already know, a human body consists of different parts. The outer parts of a body are visible, whereas the parts like brain, lungs, heart etc which are inside cannot be seen. Similarly in a computer, we can see only those parts of the hardware that are outside e.g. monitor, keyboard etc. They are attached to the CPU by cables. Some parts of hardware are inside the CPU. We can see them when we open the body of a CPU box e.g. Hard disk, CPU chip etc.

Main Parts of a Computer

A computer has the following four main parts that help in performing the IPO (Input Output Process) cycle:


A monitor looks like a TV screen. It displays the work that we do on a computer. It also displays the movement of the mouse pointer on the screen. A monitor is also known as VDU (Visual Display Unit). The information that we see on a monitor is called soft copy. There are three different types of monitors:

1. CRT (Cathode Ray Tube) Monitor: CRT monitors contain a vacuum tube and are bigger in size and consume more power.

2. LCD (Liquid Crystal Display) Monitor: LCD monitor has a flat type of screen. It consumes less power.

3. LED (Light Emitting Diode) Monitor: These monitors have better display. These are thinner and lighter in weight. LED monitors use 40% less power than LCDs and last longer. These are the most commonly used monitors today.

CPU (Central Processing Unit)

It is the brain of a computer that processes all the instructions given to the computer. It solves all calculations and displays the result on the monitor. It also stores a lot of information.

A CPU is made up of three main parts they are MU, CU and ALU.

MU (Memory Unit): In this unit, we can store data and instructions which are to be processed and are then passed on to ALU or CU.

CU (Control Unit): The control unit works like a traffic policeman. It controls and manages the working of all the parts of a computer.

ALU (Arithmetic Logic Unit): This unit performs all arithmetic calculations like addition, subtraction, multiplication and division. It also performs logical operations like finding the greater number(>), smaller number(<), greater than equal to(>=), less than equal to(<=), or equal to and not equal to(<>) numbers.


A keyboard is used to type data and instructions into the computer. The commonly used keyboard has 104 keys which can be divided into many groups based on their functions.

1. Typing Keys: These keys include letters (Alphabet keys), numbers (Number keys), punctuation  and special symbol keys. These keys also include the Shift, Caps Lock, Spacebar, Backspace and the Tab keys.

2. Control Keys: These keys are either used alone or in combination with other keys to perform certain actions. Ctrl, Alt, Windows logo key and the Esc key are the various examples of control keys.

3. Function Keys: These are used to perform specific tasks. These keys are placed on the top row of the keyboard and are labelled as F1...F12. These keys have different functions in different programs.

4. Numeric Keypad: The numeric keypad consist of number keys from (0 to 9) the arithmetic operators and the decimal point, similar to the keys of a calculator. It is placed on the right side of the keyboard and is used for entering numbers at a fast speed.

5. Navigation Keys: These keys are used to move through the documents or web pages and editing the text. These keys include: 

Arrow Keys: These keys are used to move the cursor on the screen.

Home: Move the cursor to the beginning of a line. 

End: Moves the cursor to the end of a line.

Page Up: Moves the cursor or page up by one screen.

Page Down: Moves the cursor or page down by one screen.

Delete: Erases the character after the cursor or the selected text.

Insert: Turn the Insert mode on or off.


A mouse is a pointing device. It is connected to the CPU by a cable. A mouse usually has two buttons on it. It is used to point, select and move any object on the screen. When we move the cursor with our hand, a pointer on the screen moves in the same direction. It also helps to draw pictures. Nowadays, the scroll mouse is more in use, that has a scroll wheel in the center of the two buttons.

Other Hardware Devices

Touch Screen: A touch screen is a computer screen that is sensitive to the touch. We can select the objects directly by touching with fingers without using any pointer device. For example Tablets, laptops, ATMs, Cell phones etc.

Scanner: It is a device that reads the text or pictures printed on a paper and translates the information into a form that only a computer understands. There are mainly three types of scanners: Flat bed scanner, sheet fed scanner and hand held scanner.

Printer: A Printer prints the output you see on the computer screen on a paper. The output printed on a paper is called hard copy.

Plotter: A Plotter is a kind of printer for computers. It is used to print on very large size papers. Plotters print their output by moving coloured pens across the surface of a piece of paper. They are generally used for flex printing. They can drew complex line art, including text, but do so very slowly because of the mechanical movement of the pens.

Speakers: Speakers are used to listen to music and sounds stored in a computer.

Light Pen: It looks like a pen that can be used on a special pad. Whatever you write on its pad is visible on the monitor.

Joystick: It is used for playing games. It helps to move the items on the screen.

Pen Drive: A pen drive is very small in size, but can store and transfer data from one computer to another. It is easy to carry and handle.

Hard Disk: A hard disk is a device that can store large amounts of information. It is present inside the CPU.

CD: CD stands for Compact Disk. It is round, flat and shiny disk that stores a lot of information.

Microphone: A microphone is used to record our voice and different sounds into a computer. It also helps us to talk to our relatives and friends through the internet.


Software is that part of a computer, which cannot be touched. To make the hardware work, we need to have software installed in it. Software is a set of instructions given to do a particular work. There are two types of software:

1. System Software: It is a set of programs that controls the overall working of a computer. For example, Operating system is a part of system software that makes a computer run. It manages all the input and output operations.

2. Application Software: The software that helps you to do a specific type of work is Application software. Some popular examples of Application software are: Microsoft word, Power-point, Microsoft excel and MS Paint.

Working of a Computer

Every computer works by following the steps given below:

Input: The data and instructions, which we enter using a keyboard or a mouse into a computer are called Input. We can enter numbers, words, pictures and sounds as input.

Processing: After entering data and instructions in a computer, the CPU works on the input and perform the given tasks. This is called processing.

Output: After processing, the CPU gives the result and displays it on the monitor which is called Ouput.

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