VM (often: VM/CMS) refers to a family of IBM virtual machine operating systems used on IBM mainframes System/370, System/390, zSeries, System z and compatible systems, including the Hercules emulator for personal computers. The first version, released in 1972, was VM/370, or officially Virtual Machine Facility/370. This was a System/370 reimplementation of earlier CP/CMS operating system. Milestone versions included VM/SP.[1] The current version is z/VM, and is still widely used as one of the main full virtualization solutions for the mainframe market. VM's differences with other IBM mainframe operating systems are primarily due to the unique circumstances in which CP/CMS was built and distributed. [1] The latest public domain version of this OS is release 6 which was made available in 1979.


If you would like to run this mainframe OS on your PC check out

Getting Started With VM/370 On the PC


Test Drive A VM370 User Logon

Glossary Common Messages White Papers
Console Commands How To's VM Control Files
Websites of Interest Vintage VM Books Mainframe Photo Gallery
VM Editor Reference Forum Messages Group A Group B *

Quick Beginner's Gotcha List

  1. Message ?CP: ACCESS or related - You are in CP mode and need to switch to CMS mode by typing "IPL CMS".

  2. When logging in you get a single response of "restart" instead of a logon message - You need to use the "clear screen" key on your 3270 emulator before logging in.

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