DOS

Acronym for Disk Operating System, DOS is the original operating system developed for the Personal Computer.

DOS 1.x & 2.x were run from a floppy disk and did not support a hard drive.

The last version by Microsoft was 6.22. By then Windows 3.11, not an operating system yet but a GUI interface running under DOS, was being converted to a full-flown OS, called Windows 95.

DOS was quite similar to UNIX, in that it was command-line based.