The subsystem is where work is processed on the system. A subsystem is a single, predefined operating environment through which the system coordinates the work flow and resource use. The system can contain several subsystems, all operating independently of each other. Subsystems manage resources.

All jobs, with the exception of system jobs, run within subsystems. Each subsystem can run unique operations. For instance, one subsystem may be set up to handle only interactive jobs, while another subsystem handles only batch jobs. Subsystems can also be designed to handle many types of work. The system allows you to decide the number of subsystems and what types of work each subsystem handles.

The run-time characteristics of a subsystem are defined in an object called a subsystem description. For example, if you want to permanently change the amount of work (number of jobs) coming from a job queue into a subsystem you only need to change the job queue entry in the subsystem description.