Although the terms ''PR/SM'' and ''LPAR'' are often used interchangeably in IBM Z, including in IBM documentation, ''PR/SM'' was not present in the [[IBM 370System/370 Model 168]]'s [[VM (operating system)|Virtual Machine Facility/370]]; it came in with the [[IBM 3090]], years later. Formally, LPAR designates the mode of operation or an individual logical partition, whereas PR/SM is the commercial designation of the feature.<ref name="Singh"/>{{rp|83}} In mainframe computing '''PR/SM''' ('''Processor Resource/System Manager''') is a type-1 [[Hypervisor]] (a [[virtual machine]] monitor) that allows multiple [[LPAR|logical partition]]s to share physical resources such as [[Central processing unit|CPU]]s, [[Channel I/O|I/O channels]] and LAN interfaces; when sharing channels, the LPARs can share I/O devices such as [[direct access storage device]]s (DASD). PR/SM is integrated with all [[IBM System z]] machines. Similar facilities exist on the [[IBM Power Systems]] family, and its predecessors.
[[IBM]] introduced PR/SM in 1988 with the [[IBM 3090]] processors.<ref>{{cite web|url=http://www.redbooks.ibm.com/redpapers/pdfs/redp5157.pdf|title=IBM Z Functional Matrix|author1=Frank Packheiser|author2=Octavian Lascu|author3=Bill White|page=18|publisher=[[IBM]]|date=2018}}</ref>
