1. Allows the user and the computer to communicate with each other.
User Interfaces
Allows the user and the computer to communicate with each other.

2. Three different types of User interfaces
Command-line interface Menu driven interface Graphical User Interface (G.U.I.)

3. Command-line
User enters structured commands through the keyboard. The user must remember the exact command and the syntax MS DOS (Disk operating System) and Unix are O.S. that use command line E.g. start

5. Menu Driven Interface
List of options that allow the user to select from.

6. Graphical User Interface
WIMP (windows icons menus pull down and pop ups Easy to understand, very user friendly Use both mouse and keyboard Windows XP, Vista