Microsoft's DOS (Disk Operating System) is a command line user interface. MS-DOS 1.0 was released in 1981 for IBM computers and the latest version of MS-DOS is MS-DOS 6.22 released in 1994. While MS-DOS is not commonly used by itself today, it still can be accessed from Windows 95, Windows 98 or Windows ME by clicking Start / Run and typing command or CMD in Windows NT, 2000 or XP.