CP/M, short for Control Program for Microcomputers, was a mass-market operating system created for Intel 8080/85-based microcomputers by Gary Kildall of Digital Research, Inc, Initially confined to single-tasking on 8-bit processors and no more than 64 kilobytes of memory. later versions of CP/M added multi-user variations and were migrated to 16-bit processors.

The combination of CP/M and S-100 bus computers loosely patterned on the MITS Altair was an early industry standard for microcomputers, and this computer platform was widely used in business through the late 1970s and into the mid-1980s. CP/M increased the market size for both hardware and software by greatly reducing the amount of programming required to install an application on a new manufacturer's computer. An important driver of software innovation was the advent of (comparatively) low-cost microcomputers running CP/M, as independent programmers and hackers bought them and shared their creations in user groups. CP/M was displaced by MS-DOS soon after the 1982 introduction of the IBM PC.

CP/M-86 was a version of the CP/M operating system that Digital Research (DR) made for the Intel 8086 and Intel 8088. The system commands are the same as CP/M-80. Executable files used the relocatable .CMD file format (the same filename extension .CMD is used by Microsoft Windows for unrelated batch files). Digital Research also produced a multi-user multitasking operating system compatible with CP/M-86, MP/M-86, which later evolved into Concurrent CP/M-86. When an emulator was added to provide PC DOS compatibility, the system was renamed Concurrent DOS, which later became Multiuser DOS. The DOS Plus, FlexOS, and DR DOS families of operating systems started as derivations of Concurrent DOS.

IBM PC

When IBM contacted other companies to obtain components for the IBM PC, the as-yet unreleased CP/M-86 was its first choice for an operating system because CP/M had the most applications at the time. Negotiations between Digital Research and IBM quickly deteriorated over IBM's non-disclosure agreement and its insistence on a one-time fee rather than DRI's usual royalty licensing plan. After discussions with Microsoft, IBM decided to use 86-DOS (QDOS), a CP/M-like operating system that Microsoft bought from Seattle Computer. Microsoft adapted it for PC, and licensed it to IBM. It was sold by IBM under the name of PC DOS. When PC-clones came about, other companies sold it under the name of MS-DOS. After learning about the deal, Digital Research founder Gary Kildall threatened to sue IBM for infringing DRI's intellectual property, and IBM agreed to offer CP/M-86 as an alternative operating system on the PC to settle the claim.