Classification of computers

According to the technology used, computers can be classified as
1. Digital Computers
2. Analog Computers
3. Hybrid Computers

Digital Computers are the most common computers being used like calculators, digital watches etc. They store data and instructions in the form of binary digits i.e. 0 and 1. These digits are used to denote letters, numerals and symbols.

Analog Computers measure continuous variations in devices like speedometer, thermometer, voltmeter, ammeter etc. (Analog means continuous variation).

Hybrid Computers are the combination of both Digital and Analog Computers. They measure analog quantities and convert them into digital signals for analysis. They can be used in space research and satellites. Computer with multimedia, robot etc. are examples of Hybrid Computers.

Computers can also be classified according to size and storage capacity as

1. Micro Computers
2. Mini Computers
3. Main Frame Computers
4. Super Computers

Micro Computers are small computers used as personal computers, computer notebooks, palmtop, laptop etc. for entertainment, education etc, at home or at office where volume of data is less.

A Mini Computer is a multi user system. It can be used by many users simultaneously. Mini Computers have larger RAM (Random Access Memory) and storage capacity. They can process data more quickly. Reservation system, banking system, etc. are using Mini Computers.


Main Frame Computers are large and powerful. They are used for complex calculations. They can support many input and output devices. They can process large amount of data quickly. They have a high storage capacity.


Super Computers are the largest, fastest, and most expensive computers used in the fields of medicines, industries, space research etc.They have many processing units working simultaneously to perform billions of operations every second.

Input and output devices of a computer

The devices that help the user to communicate with the computer are input devices. Once the data is fed into the computer, it works on the data, processes it and provides the results to the user. The devices that help the user to get the output from the computer are output devices.

Input devices
Input devices are those devices that are used to feed data and programs into a computer.

• Keyboard: the keyboard of a computer resembles a typewriter with a few additional keys to handle various functions. A computer keyboard has three categories of keys:
  Alphanumeric keys: Alphabets, numbers, characters.
  Special keys: enter, backspace, Del, esc, Ctrl, alt.
  Function keys: (f1 to f 12) for selected operations.
• Mouse: the mouse is one of the most popular input devices. This device helps you to manipulate a pointer or an arrow on the screen. The pointer moves according to the movement of the mouse on a flat surface.
• Light pen: helps in identifying bar codes.
• Scanner: scans documents and photos and transmits them to the computer.
• Microphone: helps to record sounds to the computer and extensively used to talk through the internet.
• Web camera: Also called webcam is a small low resolution digital video camera. Web accessible cameras upload images to a web server.
• Joystick: used mainly to play games.

Output devices
These are the devices that are useful in receiving information or processed data from the computer. Some of the commonly used output devices are

• Visual display unit: the unit that resembles a TV screen and commonly referred to as ‘Monitor’. This unit informs us about the activities performed by the computer.
• Printers: printers are the primary output device used to prepare permanent documents. The printers that are widely used are Dot Matrix, LaserJet and Inkjet.
• Plotters: plotters are used for high quality diagrams. A pen is mounted on an arm, which moves along the paper with the help of motors. This is used in making high-resolution sketches and maps.
• Speakers: helps in listening to music and soundtracks of applications.

Input/output devices
The information in the disks is read by a disk drive. It is this same drive, which helps in writing or recording information to the disks (hard disk, floppy disk, CD R/RW). Hence, the disk drive is called an input/output device.