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| Developer | IBM |
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| Marketing target | IBM mainframe computers |
| License | Proprietary |
| History of IBM mainframe operating systems |
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Group Control System (GCS) is an operating system made by IBM, meant to run as a guest of VM. 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.
GCS's purpose is to provide an environment to run some specific OS/MVS-based applications and networking middleware under VM. To this end, GCS provides a limited simulation of the OS/MVS APIs. While CMS, the usual VM guest, already has OS simulation, it is not extensive enough to run some applications such as VTAM.
Specifically, GCS provides 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:
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:
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The history of IBM mainframe operating systems is significant within the history of mainframe operating systems, because of IBM's long-standing position as the world's largest hardware supplier of mainframe computers. IBM mainframes run operating systems supplied by IBM and by third parties.
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Remote Spooling Communications Subsystem or RSCS is a subsystem of IBM's VM/370 operating system which accepts files transmitted to it from local or remote system and users and transmits them to destination local or remote users and systems. RSCS also transmits commands and messages among users and systems.
In computing, a system virtual machine is a virtual machine (VM) that provides a complete system platform and supports the execution of a complete operating system (OS). These usually emulate an existing architecture, and are built with the purpose of either providing a platform to run programs where the real hardware is not available for use, or of having multiple instances of virtual machines leading to more efficient use of computing resources, both in terms of energy consumption and cost effectiveness, or both. A VM was originally defined by Popek and Goldberg as "an efficient, isolated duplicate of a real machine".
