Every computer has an operating system, which is a sort of master program that runs automatically when you switch the computer on, and continues running till you switch off. It is responsible for the many routine tasks required to keep a computer running : moving the pointer when you move the mouse, providing icons and menus, running other programs such as a word processor or a game which you may request, controlling the various disk drives, the screen and so on. The most widely used PC operating system is Microsoft- Windows.
The software that controls the allocation and usage of hardware resources such as memory, central processing unit (CPU) time, disk space, and peripheral devices. The operating system is the foundation on which programs are built.