A computer is useful only when it is able to communicate with the external environment. When you work with the computer you feed your data and instructions through some device to the computer. These devices are called Input devices. Similarly computer after processing gives output through other devices called output devices.
For a particular application one form of device is more desirable compared to others. We will discuss various types of Input-Output devices that are used for different types of applications. They are also known as peripheral devices because they surround the CPU and make a communication between computer and the outer world.