View source for Group Control System

{{Short description|IBM operating system}}
{{More citations needed|date=November 2024}}
{{Infobox OS
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| marketing target       = [[IBM mainframes|IBM mainframe computers]]
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{{History of IBM mainframe operating systems}}
'''Group Control System''' ('''GCS''') is an [[operating system]] made by [[IBM]], meant to run as a guest of [[VM (operating system)|VM]].<ref>{{Cite web |title=What GCS Is | website=[[IBM]] |url=https://www.ibm.com/docs/en/zvm/7.2?topic=overview-what-gcs-is}}</ref> GCS is an integral component of the discontinued [[VM/SP]] (since VM/SP 4), VM/XA SP, [[VM/ESA]] and current [[z/VM]] IBM System product offerings.
==Overview==
GCS's purpose is to provide an environment to run some specific [[MVS|OS/MVS]]-based applications and networking [[middleware]] under VM. To this end, GCS provides a limited simulation of the OS/MVS APIs. While [[Conversational Monitor System|CMS]], the usual VM guest, already has OS simulation, it is not extensive enough to run some applications such as [[VTAM]].
Specifically, GCS provides [[Computer multitasking|OS multitasking]] support. In order to be able to spread the load over several virtual machines, GCS also implements a notion of group where each group member virtual machine can interact with one another.
To implement this, GCS uses several techniques:
* A writable shared segment
* [[IUCV]] communications between virtual machines
* A recovery virtual machine, designed to clean up locks in the shared segments when virtual machines unexpectedly leave the group
GCS is not designed to be a multi-purpose user operating system such as CMS. For example, it does not allow for file editing.
Examples of programs designed to run under GCS are:
* VM/VTAM : The VM implementation of the VTAM stack
* [[RSCS]] : The Remote Spooling Communication Subsystem, which, when associated with an instance of VM/VTAM, can use SNA resources to communicate with other SNA/NJE hosts
* [[NETVIEW]] : A networking monitoring service
== References ==
{{reflist}}
== External links ==
* [https://archive.today/20121210084740/http://publibz.boulder.ibm.com/cgi-bin/bookmgr_OS390/BOOKS/HCSF5B20/CCONTENTS?SHELF=EZ2ZVM01&DN=SC24-6098-02&DT=20070419173550 z/VM 5.3 Group Control System]
{{IBM operating systems}}
{{DEFAULTSORT:Group Control System(Vm)}}
[[Category:IBM mainframe operating systems]]
[[Category:VM (operating system)]]
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