(
Operating
System) The master control program in a computer or mobile device. The O-S acronym has been part of the names of various operating systems. Microsoft used DOS for many years in the PC, and Apple used OS 8, OS 9 and OS X in the Mac. Some of the operating systems in this encyclopedia that have OS in their name are
TOS,
DOS,
PC-DOS,
MS-DOS,
DR-DOS,
macOS,
Mac OS X,
iOS,
OS/390 and
OS/400. For the major functions operating systems perform, see
operating system.