MS-DOS

(pronounced: M-S dahss)

The standard operating system for IBM personal computers. Introduced in 1981, MS-DOS was originally developed by Microsoft for IBM.

The most severe limitation was its 640K RAM barrier; Windows helped alleviate some of its problems but still "sits on top of DOS" and relies on it for many services. Newer operating systems, such as Windows NT, XP, and OS/2 Warp (and the Macintosh operating system), do not rely on DOS to the same extent or at all, although most can execute DOS-based programs. It is expected that DOS will eventually disappear.