Every computer must have an operating system to run other programmes. Operating system is the most important programme that runs on a computer. Operating systems perform basic tasks, such as recognizing input from the keyboard, sending output to the display screen, keeping track of files and directories on the disk, and controlling peripheral devices such as disk drives and printers.
Operating systems provide a software platform on top of which other programmes, calledapplication programmes, can run. The application programmes must be written to run on top of a particular operating system. Your choice of operating system, therefore, determines to a great extent the applications you can run. For PCs, the most popular operating systems are DOS, OS/2, and Windows.