CP/CMS was a time-sharing operating system of the late 60s and early 70s, known for its excellent performance and advanced features. It had three distinct versions:
* CP-40/CMS, an important "one-off" research system that established the CP/CMS virtual machine architecture
* CP-67/CMS, a reimplementation of CP-40/CMS for the IBM System/360-67, and the primary focus of this article
* CP-370/CMS, a reimplementation of CP-67/CMS for the System/370 – never released as such, but became the foundation of IBM's VM/370 operating system, announced in 1972.
Each implementation was a substantial redesign of its predecessor and an evolutionary step forward. CP-67/CMS was the first widely-available virtual machine architecture. IBM pioneered this idea with its research systems M44/44X (which used partial virtualization) and CP-40 (which used full virtualization).
In addition to its role as the predecessor of the VM family, CP/CMS played an important role in the development of operating system (OS) theory, the design of IBM's System/370, the time-sharing industry, and the creation of a self-supporting user community that anticipated today's free software movement.