All work the system performs is done in subsystems. Think of a subsystem as a department in your company. Employees belong to one department or another. Each department specializes in some kind of work, such as sales, accounting, marketing, production, or shipping. By the same token, subsystems are also specialized. There is, however, one general-purpose subsystem, called QBASE.
You can run your system using QBASE to do all the work, or you can split the work among several subsystems. IBM ships the i5 with the QBASE option.
Initially, you will be running your system in QBASE, a general-purpose subsystem provided by IBM. Using QBASE has certain advantages and disadvantages that will be explored in this section.
When you use QBASE, all interactive and batch jobs run in QBASE.
The main advantage of running your system in QBASE is the simplicity of management, because you need to control only one subsystem.
For example, you can work with all jobs using the Work with Subsystem Jobs (WRKSBSJOB) command by supplying QBASE as the subsystem name. Also, you can power down the system by ending subsystem QBASE using the ENDSBS command, instead of specifying *ALL and waiting for all subsystems to end.
If you have no knowledge of i5/OS, you may wish to keep QBASE at first. It will simplify your job enormously. Give yourself some time to learn and understand the concepts behind subsystems, and then you can think about using other subsystems.
Think again of the office analogy. You wouldn't consider grouping all employees in a single department and making them wear several hats so that every employee had to do some accounting, some receiving, some manufacturing, and some sales. Specialization brings efficiency.
In the same way, subsystem QBASE is inefficient because that one subsystem is forced to do everything. You can't tune your system well in these conditions. It is possible that the i5 will not perform well using only the QBASE subsystem.
Before you change your system to work with multiple subsystems, learn about work management. This chapter contains basic information about work management, but you should also consider reading IBM's Work Management Guide, which contains a full treatment of the topic.
To change from QBASE to multiple subsystems, you only needto change system value QCTLSBSD from "QBASE" to "QCTL." System value QCTLSBSD contains the name of the controlling subsystem. When you change QCTLSBSD to QCTL, the system understands that you want to start using multiple subsystems.
To change, run the Work with System Values (WRKSYSVAL) command, as follows:
Now key in option 2 (to change) and press Enter. The system shows the current value (QBASE). Type the word QCTL over it and press Enter.
This change will not become effective until you IPL the system. You don't have to IPL the system immediately, but you can if you desire.