Subsystems

The subsystem is where work is processed on the iSeries™ server. 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 will handle.

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.

• The controlling subsystem
  The controlling subsystem is the interactive subsystem that starts automatically when the system starts, and it is the subsystem through which the system operator controls the system via the system console. It is identified in the Controlling subsystem/library (QCTLSBSD) system value.
• Why consider multiple subsystems
  As the number of users on the system increases, a single subsystem for a set of work is often insufficient. By dividing your users into multiple subsystems you gain several advantages.
• Subsystem description
  A subsystem description is a system object that contains information defining the characteristics of an operating environment controlled by the system. The system-recognized identifier for the object type is *SBSD. A subsystem description defines how, where, and how much work enters a subsystem, and which resources the subsystem uses to perform the work. An active subsystem takes on the simple name of the subsystem description.
• How a subsystem starts
  When a subsystem starts, the system allocates several items and starts autostart and prestart jobs before the subsystem is ready for work.