(CP/M) An early microcomputer operating system written by Gary Kildall of Digital Research for 8080 and Zilog Z80-based 8-bit computers. CP/M was very popular in the late 1970s but was virtually wiped out by MS-DOS after the release of the IBM PC in 1981.

Many of CP/M's features and conventions strongly resemble those of early DEC operating systems such as TOPS-10, OS/8, RSTS and RSX-11.

CP/M might have been the OS for the IBM PC instead of MS-DOS but Kildall wanted to keep control of his creation and only license it to IBM. Big Blue however wanted to own and control it completely. Kildall spent the day IBM's reps wanted to meet him enjoying the perfect flying weather in his private plane.