Disk operating system

A disk operating system, or DOS, is an operating system that requires a hard disk, floppy disk, solid-state drive or other direct-access storage device as its secondary storage, and that provides a file system and a way to load and run programs stored on that disk. The term is now historical, because almost every general-purpose operating system today expects such storage. As disk drives grew larger and cheaper in the early 1960s, mainframe and minicomputer vendors introduced disk operating systems or adapted existing ones, and by the time IBM announced the System/360 the idea was well established, with DOS/360 and OS/360 in common use. Most home and personal computers of the late 1970s and 1980s used one, often with DOS in the name, such as Apple DOS, Atari DOS, TRS-DOS and MS-DOS, while CP/M was one without the word in its name.