Group Control System (GCS) is an

operating system An operating system (OS) is system software that manages computer hardware and software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ...

made by

IBM International Business Machines Corporation (using the trademark IBM), nicknamed Big Blue, is an American Multinational corporation, multinational technology company headquartered in Armonk, New York, and present in over 175 countries. It is ...

, 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 z/VM is the current version in IBM's VM family of virtual machine operating systems. First released in October 2000, z/VM remains in active use and development . It is directly based on technology and concepts dating back to the 1960s, particu ...

IBM System product offerings.

Overview

GCS's purpose is to provide an environment to run some specific OS/MVS-based applications and networking

middleware Middleware is a type of computer software program that provides services to software applications beyond those available from the operating system. It can be described as "software glue". Middleware makes it easier for software developers to imple ...

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 Virtual Telecommunications Access Method (VTAM) is the IBM subsystem that implements Systems Network Architecture (SNA) for mainframe environments. VTAM provides an application programming interface (API) for communication applications, and contro ...

. 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: * 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 Remote Spooling Communications Subsystem or RSCS is a subsystem ("virtual machine" in VM terminology) 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 loc ...

: 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

External links

z/VM 5.3 Group Control System
IBM mainframe operating systems VM (operating system) {{mainframe-compu-stub