Group Control System (GCS) is an

operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also in ...

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 VM (often: VM/CMS) is a family of IBM virtual machine operating systems used on IBM mainframes System/370, System/390, zSeries, System z and compatible systems, including the Hercules emulator for personal computers. The following versions ...

and current z/VM IBM System product offerings.

Overview

GCS's purpose is to provide an environment to run some specific

OS/MVS Multiple Virtual Storage, more commonly called MVS, was the most commonly used operating system on the System/370 and System/390 IBM mainframe computers. IBM developed MVS, along with OS/VS1 and SVS, as a successor to OS/360. It is unrelated ...

-based applications and networking

middleware Middleware is a type of computer software 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 implement co ...

under VM. To this end, GCS provides a limited simulation of the OS/MVS APIs. While

CMS CMS may refer to: Computing * Call management system * CMS-2 (programming language), used by the United States Navy * Code Morphing Software, a technology used by Transmeta * Collection management system for a museum collection * Color managem ...

, 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 c ...

. 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 Inter User Communication Vehicle (IUCV) is a data transfer mechanism in IBM VM line of operating systems. It was introduced with VM/SP Release 1 in 1980. It allows establishment of point to point communication channels, either between two virtual ...

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

External links

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