Input devices

Keyboards

The most common method of data input device is the QWERTY keyboard (so named because of the order of the first few characters on the top row of letters reading from left to right. This is now
the standard layout for keyboards in most countries of the world. The computer continuously scans the keyboard and when a key is pressed, a signal is sent to the CPU using the code for the particular character represented by the key.

How Keyboards 
are used
• On-line data entry.
Data is input straight into the computer for processing.
• Off-line data entry.
This is usually achieved by methods known as key-to-disk or key-to-tape. As data is
typed using a keyboard, it is recorded on disk or tape. The data is later transferred from
the disk or tape to a computer for processing.

Mouse
A mouse is used to input data in two different ways.Firstly, as the mouse is moved, a ball underneath it revolves and this movement is detected by sensors which relay the data to the CPU. Secondly, buttons on the mouse act in a similar way to keys on a keyboard. When they are pressed, the code for the relevant control character is sent to the CPU.

Tracker Ball
A tracker ball is rotated by hand and as in the case of the mouse, sensors detect the
movement of the ball and relay the data to the CPU. The advantage of a tracker ball over a
mouse is that it remains stationary and therefore does not require as much space as a
mouse.

Joystick

A joystick consists of a small lever which is moved by the user to control movement on a
screen. Sensors detect the movement of the lever and relay the data to the CPU.