Input Device :)

An input device is a peripheral used to transfer data from the outside world into a computer system. In other words, it is any machine that feeds data into a computer.

Input devices convert the user's actions and analog data (sound, graphics, pictures) into digital electronic signals that can be ‘handled’ or ‘read’ by a computer. Digital data (such as from barcode readers, scanners, etc.) does not require any conversion and is input direct into a computer. It is through input devices that a user exercises control over a computer, its operations, and outputs.

Examples of input devices are:

Keyboard
Mouse
Light pen
Joystick
Scanner
Touch screen
Digitising tablet
Microphone
Barcode reader.
Graphic tablet
Magnetic-stripe reader

All the devices above feed data or instruction into a computer for display, processing, storage, or outputting.

CLASSIFICATION OF INPUT DEVICES
Many input devices can be classified according to:

the modality of input (e.g. mechanical motion, audio, visual, sound, etc.)
whether the input is discrete (e.g. keypresses) or continuous (e.g. a mouse's position, though digitized into a discrete quantity, is high-resolution enough to be thought of as continuous)
the number of degrees of freedom involved (e.g. many mice allow 2D positional input, but some devices allow 3D input, such as the Logitech Magellan Space Mouse)

Pointing devices, which are input devices used to specify a position in space, can further be classified according to
Whether the input is direct or indirect. With direct input, the input space coincides with the display space, i.e. pointing is done in the space where visual feedback or the cursor appears. Touchscreens and light pens involve direct input. Examples involving indirect input include the mouse and trackball.
Whether the positional information is absolute (e.g. on a touch screen) or relative (e.g. with a mouse that can be lifted and repositioned)

Note that direct input is almost necessarily absolute, but indirect input may be either absolute or relative. For example, digitizing graphics tablets that do not have an embedded screen involve indirect input, and sense absolute positions and are often run in an absolute input mode, but they may also be setup to simulate a relative input mode where the stylus or puck can be lifted and repositioned.