Group Control System

Group Control System

GCS - VM Group Control System is a VM guest operating system

Its 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 already has OS simulation, it is not extensive enough to run some applications such as VTAM and VTAM applications.

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 writeable shared segment
• IUCV communications between virtual machines
• A recovery virtual machine - designed to cleanup locks in the shared segments when virtual machines unexpectedly leave the group

GCS is not designed to be a multi-purpose user operating system (like 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

External References

• z/VM 5.3 Group Control System