A single user operating system that runs one program at a time and is limited to working with one megabyte of memory, 640 kilobytes of which is usable for the application program. Add-ons to DOS, such as Microsoft Windows, allow the user to have multiple applications loaded at once and switch between them.
The DOS produced by Microsoft. Early versions of it bear striking similarities to the earlier CP/M, but it utilizes simpler commands. It provides only a CLI, but either OS/2, Windows 3.1, Windows '95, Windows '98, Windows ME, or GEOS may be run on top of it to provide a GUI. It only runs on x86 based machines.