VM/CMS

from The Free On-line Dictionary of Computing (8 July 2008)

Virtual Machine/Conversational Monitor System
Conversational Monitor System
VM/CMS

   <operating system> (VM/CMS) An {IBM} {time-sharing} and
   personal computing environment executing under {Virtual
   Machine} (VM) in a virtual machine environment.  VM/CMS is
   designed to support large numbers of {interactive} users.  It
   relies on numerous {APIs} into the {Control Program} (CP) to
   provide very efficient single-user processing

   VM/CMS was only adopted some time after the original design of
   {Virtual Machine} as a more efficient personal computing
   environment than {MVS/TSO}.

   (1999-01-19)

from V.E.R.A. -- Virtual Entity of Relevant Acronyms (June 2006)

VMCMS
       Virtual Machine / Conversational Monitoring System (IBM, VM),
"VM/CMS"