Stands for “Disk Operating system”, developed by IBM (international Business Machine). DOS is Stands for frequently used to explain MS-DOS the Windows command line as well as.

DOS uses a command line, or text-based interface, that allows the user to type commands.

DOS describes any OS that operates from the disk drive. All operating systems can be viewed as computer systems, today.
Dozens of other operating systems also use the acronym “DOS”, including the 1960s DOS/360. Others are Apple DOS, Apple ProDOS, Atari DOS, Commodore DOS, TRSDOS, and AmigaDOS. See List of DOS operating systems § Other operating systems.

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The hard disk was invented on September 13, 1956 by IBM team led by Rey Johnson (considered as “father” of the disk drive). Earlier hard disk drives were large and cumbersome devices.