An operating system is a program which acts as an interface between a user of a computer and the computer hardware. The purpose of an operating system is to provide an environment in which a user may execute programs. The primary goal of an operating is thus to make the computer system convenient to use. OS is the most important program that run of a computer. operating system perform basic tasks such as recognizing input from the keyboard, sending output to the monitor, keeping track of files and directories on the disk and controlling peripheral devices such as disk drive and printers. Examples of popular microcomputer OS are Windows, DOS, OS/2 for PCs and Mac OS for Apple computer, etc.