Execute Channel Program in Real Storage: Difference between revisions

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Revision as of 10:48, 4 July 2021

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{{refimprove|date=August 2019}}

In [[IBM mainframe]] [[operating system]]s, '''Execute Channel Program in Real Storage''' ('''EXCPVR''') is a [[Macro (computer science)|macro]] generating a [[system call]], implemented as a [[Supervisor Call instruction]], for low-level device access, where the programmer is responsible for providing a list of device-specific [[Channel_command_word#Channel_command_words|CCWs]], that is, a [[Channel_program#Channel_Program|channel program]], to be executed by I/O channels, control units and devices.<ref name="Murphy1995">{{cite book|author=Hank A. Murphy|title=MVS control blocks|year=1995|publisher=McGraw-Hill Ryerson, Limited|isbn=978-0-07-044309-9|pages=121, 134–135}}</ref> Additionally, the programmer is expected and required to ensure that the input/output data areas are in real storage and are "fixed", either prior to invoking EXCPVR or via the page fix appendage. EXCPVR can in some situations provide improved performance compared to EXCP.<ref name="Sacks1994">{{cite book|author=David J. Sacks|title=MVS Answer Book|date=16 March 1994|publisher=Wiley|isbn=978-0-471-60821-9|page=74}}</ref>

==Relationship to Execute Channel Program (EXCP)==