Operating system The most fundamental software run on a computer. All computers have an operating system, which is used among other things to start and run other programs. The operating system performs important tasks, such as receiving data from the keyboard and mouse, sending data to the screen, keeping files and folders under control and checking the various units in the machine (e.g. disks, printers etc). An operating system as a rule also contains a user interface, which for example enables the user to control the machine using graphic icons, windows and menus. Examples are Windows 98, Windows 2000, Windows XP, UNIX-Solaris, AIX, MacOS, Linux.