1. INPUT-  Whatever goes into the computer. Input can take a variety of forms, from commands you enter from the keyboard to data from another computer or device. A device that feeds data into a computer, such as a keyboard or mouse, is called an input device. The act of entering data into a computer.
     A program  an organized list of instructions that, when executed, causes the computer to behave in a predetermined manner. Without programs, computers are useless. A command an instruction to a computer or device to perform a specific task. Commands come in different forms. They can be special words (keywords) that a program understands, function keys , choices in a menu, buttons or other graphical objects on your screen. A response a common authentication technique whereby an individual is prompted (the challenge) to provide some private information (the response).

2.
alphanumeric keys - letters and numbers
punctuation keys - comma, period, semicolon, and so on.
special keys - function keys, control keys, arrow keys, Caps Lock key, and so on.
  A keyboards for mobile computer

3.
mechanical - has a rubber or metal ball on its underside that can roll in all directions. Mechanical sensors within the mouse detect the direction the ball is rolling and move the screen pointer accordingly.
optomechanical - same as a mechanical mouse, but uses optical sensors to detect motion of the ball.
optical - uses a laser to detect the mouse's movement. You must move the mouse along a special mat with a grid so that the optical mechanism has a frame of reference. Optical mice have no mechanical moving parts. They respond more quickly and precisely than mechanical and optomechanical mice, but they are also more expensive.

4.  types of touch screen

• conductive
• resistive
• protective layer

Touch-sensitive pad used as a pointing device on some portable computers. By moving a finger or other object along the pad, you can move the pointer on the display screen. And you click by tapping the pad.