MS DOS (1981)
Microsoft DOS (Disk Operating System) is a command line user interface.
Microsoft releases MS-DOS 1.0 to IBM, for the original IBM PC in 1981.
In 1982 MS-DOS 1.1 supports 320KB double-sided floppy disk drives.
Microsoft also releases MS-DOS 1.25, similar to 1.1 but for IBM-compatible computers with 720 KB floppy disk drives.