Input unit is used to hold the input data for processing. It sends the input data to the central processing unit(CPU). The typical devices which are used for inputting the data and instructions to the computer are keyboards, paper type readers, mouse etc.
An input unit is a generalised term in computer science for any ‘device’ which can be attached to a computer system which can gather data from the real world so that it can be processed.
For example - all of these are forms of input unit :
Keyboard, Mouse, Touch pad, Graphics stylus, Touch screen, Scanner, Biometric, Camera, Microphone