How far the personal computer has evolved over the two decades since its birth in the '70s!! One of the first true computer operating systems was called 'CP/M', which stood for Control Program for Microcomputers. CP/M has long since been pushed aside by DOS, Windows, Macs, etc. (Also long gone are the days when software was written to work in a few kilobytes of RAM!)

CP/M comes/came in three main versions; 1.4, 2.2 and 3.1. v2.2 was the basis of MSDOS, while v3.1 evolved into DRDOS and OpenDOS / DR-DOS. There were also 8086 and 68000 versions of CP/M. CP/M-86 evolved into DOS Plus, Concurrent DOS and REAL/32.