Complex sentence: DOS, short for disk operating system, is an acronym used to describe the family of several very similar command-line computer operating systems, including MS-DOS, PC DOS, DR-DOS, FreeDOS, ROM-DOS, and PTS-DOS.
Split into simpler sentences: DOS, short for disk operating system, is an acronym for several computer operating systems that are operated by using the command line. "DOS" is used to describe the family of several very similar command-line systems, including MS-DOS, PC DOS, DR-DOS, FreeDOS, ROM-DOS, and PTS-DOS.