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Guy Harris (talk | contribs) →History: An IBM Systems Journal article on PR/SM suggests it's implemented with low-level hardware and microcode at a level very different from the level at which CP runs. |
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IBM developed the concept of [[hypervisor]]s ([[virtual machine]]s in [[IBM CP-40|CP-40]] and [[CP-67]]) and in 1972 provided it for the [[IBM System/370|S/370]] as [[VM (operating system)|Virtual Machine Facility/370]].<ref>{{
cite book |url=http://www.vm.ibm.com/pubs/HCSF8A50.PDF |title=z/VMbuilt on IBM Virtualization Technology General Information Version 4 Release 3.0
|id=GC24-5991-04 |date=2002-04-12 |publisher=[[IBM]]}}</ref> IBM introduced the Start Interpretive Execution (SIE) instruction (designed specifically for the execution of virtual machines) as part of 370-XA architecture on the 3081, as well as VM/XA versions of VM to exploit it. [[PR/SM]] is a type-1 Hypervisor based on the CP component of VM/XA that runs directly on the machine level and allocates system resources across LPARs to share physical resources.{{cn|date=April 2023}} It is a standard feature on [[IBM System z]] only. An IBM POWER system uses PHYP (the POWER Hypervisor) to enable its LPAR functionalities for System p and System i since approximately 2000 in POWER4 systems.
[[Amdahl Corporation]]'s Multiple Domain Facility (MDF) was introduced in 1982.<ref>{{cite journal |last1=Doran |first1=R.W. |title=Amdahl multiple-___domain architecture |journal=Computer |date=October 1988 |volume=21 |issue=10 |pages=20–28 |doi=10.1109/2.7054 |s2cid=1738798 |url=http://www-ti.informatik.uni-tuebingen.de/~spruth/edumirror/xx067.pdf |archive-url=https://web.archive.org/web/20170829211626/http://www-ti.informatik.uni-tuebingen.de/~spruth/edumirror/xx067.pdf |archive-date=2017-08-29}}</ref> IBM began marketing its functionally similar PR/SM in 1988, implemented on its [[ESA/370]] architecture released that year. MDF-based LPAR technology continued to be developed separately by Amdahl, and [[Hitachi Data Systems]] in part for their implementations of the new architecture, which featured the introduction of [[access registers]] that allowed use of multiple [[data space]]s addressable by a single [[address space]]. IBM subsequently continued its LPAR development with its 64-bit [[System z]] and [[IBM AS/400]] architectures. LPAR and PR/SM reconfigurations can be made without rebooting the computer, i.e., while some LPARs remain active. Reconfigurations can include changing channel path definitions and device definitions.
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