(Control Program for Microprocessors) A single user operating system for the 8080 and Z80 microprocessors from Caldera, known since 2002 as The SCO Group. Created by Gary Kildall of Digital Research, CP/M had its heyday in the early 1980s. It was an unsophisticated program that didn't instill much confidence in users, yet it was a major contributor to the personal computer revolution. Because the industry never standardized on a CP/M disk or video format, software publishers had to support dozens of screen displays and floppy disk versions. This chaos ensured that IBM would set the standard with its PC very quickly.

CP/M Might Have Become DOS
Although IBM asked Kildall to provide the operating system for its new PC, he did not agree to all of IBM's demands. IBM went to Microsoft, which purchased QDOS from Seattle Computer Products and turned it into PC-DOS and MS-DOS. The rest is history. The irony is that Microsoft's DOS was modeled after CP/M. Digital Research was later acquired by Novell and then Caldera.