History of IBM Mainframe Operating Systems - System/370 and Virtual Memory Operating Systems - VM/370


For more details on the early history of VM/370, see History of CP/CMS.

VM/370 combined a virtual machine facility with a single-user system called Conversational Monitor System (CMS); this combination provided time-sharing by allowing each user to run a copy of CMS on his / her own virtual machine. This combination was a direct descendant of CP/CMS. The virtual machine facility was often used for testing new software while normal production work continued on another virtual machine, and the CMS timesharing system was widely used for program development.

VM/370 was followed by a series of upgrades: VM/SEPP, VM/BSEPP, VM/SP, VM/SP HPO, VM/XA MA, VM XA/SF, VM XA/SP, VM/ESA and z/VM. IBM also produced optional microcode assists for VM and successors, to speed up the hypervisor's emulation of privileged instructions (those which only operating systems can use) on behalf of "guest" operating systems. As part of 370/Extended Architectur, IBM added the Start Interpretive Execution (SIE) instruction to allow a further speedup of the CP hypervisor.

Read more about this topic:  History Of IBM Mainframe Operating Systems, System/370 and Virtual Memory Operating Systems