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{{for|the type of disk partition|Disk partitioning#Extended partition}}
{{redirect|LPAR|the conference|Logic for Programming, Artificial Intelligence and Reasoning }}
A '''logical partition''' ('''LPAR''') is a subset of a computer's hardware resources, [[Platform virtualization|virtualized]] as a separate computer. In effect, a physical machine can be partitioned into multiple logical partitions, each hosting a separate instance of an [[operating system]].<ref name="Singh">{{cite web |url=http://www.redbooks.ibm.com/redpieces/pdfs/sg247803.pdf |title=Security on the Mainframe |date=2009-12-02 |accessdate=2010-04-06 |first=Karan |last=Singh |url-status=dead |archiveurl=https://web.archive.org/web/20110617113238/http://www.redbooks.ibm.com/redpieces/pdfs/sg247803.pdf |archivedate=2011-06-17 }}</ref>
==History==
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|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. 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.
The terms ''PR/SM'' and ''LPAR'' are often used interchangeably in IBM Z, including in IBM documentation. Formally, LPAR designates the logical partitioning function and mode of operation, whereas PR/SM is the commercial designation of the feature.<ref
[[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 |url=http://www-ti.informatik.uni-tuebingen.de/~spruth/edumirror/xx067.pdf}}</ref> IBM began marketing its functionally similar PR/SM in 1988, implemented on its [[ESA/390]] 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 System i|System i]] 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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