Disk operating system

In times when disk drives were optional rather than default features of operating systems, being a disk operating system (i.e. disk-based or disk-aware) was a mark of superiority.

A number of such systems exist; the Commodore 64 home computer had a DOS, as did (on the other end of the spectrum) IBM's [System 370]? and [System 390]? series of mainframes (DOS/VSE, Disk Operating System/Virtual? Storage Extended).

The most popular family of operating systems called "DOS" is that running on IBM PCs. The original version was provided to IBM by Microsoft, and marketed as "PC-DOS". Later versions were also sold as "MS-DOS". [Digital Research]? produced a compatible variant known as "DR-DOS", and (after a buyout) "OpenDOS". There is also a free version named "FreeDOS".

Websites:

• [FreeDOS (can be downloaded)]
• [DR-DOS]
• [PC-DOS]