The Free On-line Dictionary of Computing (30 December 2018):
Virtual Machine/System Product
(VM) An IBM pseudo-operating systemhypervisor running on IBM 370, ESA and IBM 390
VM comprises CP (Control Program) and CMS (Conversational
Monitor System) providing Hypervisor and personal computing
environments respectively. VM became most used in the early
1980s as a Hypervisor for multiple DOS/VS and DOS/VSE
systems and as IBM's internal operating system of choice. It
declined rapidly following widespread adoption of the IBM PC
and hardware partitioning in microcode on IBM mainframes
after the IBM 3090.
VM has been known as VM/SP (System Product, the successor to
CP/67), VM/XA, and currently as VM/ESA (Enterprise Systems
Architecture). VM/ESA is still in used in 1999, featuring a
web interface, Java, and DB2. It is still a major IBM
["History of VM"(?), Melinda Varian, Princeton University].