Job class

JES2 provides 38 predefined job classes—the started task control (STC) and time-sharing logons (TSU) job classes, and 36 one character (A-Z and 0-9) execution job classes. Additional user-defined 2-8 character execution job classes are supported. Up to 512 total execution job classes can exist in a MAS.

For details on adding and deleting job classes, refer to the $ADD JOBCLASS and $DEL JOBCLASS commands in JES2 Commands.
Note:
  1. The $ADD JOBCLASS command requires that all members of the new job class are running z/OS® version 2.1, or later.
  2. The $DEL JOBCLASS command can only be used for classes that were created by the $ADD JOBCLASS command.
  3. None of the 38 predefined job classes can be deleted; however, they can be marked as inactive.

The CLASS= keyword on the JOB statement identifies the execution class for the job. If not coded on the JOB statement, the class associated with the particular device that the job entered the system on becomes the job's execution class. The INTRDR initialization statement defines a logical device for jobs entering the system through the internal reader facility.

There are no absolute rules for assigning job classes, and some experimentation is necessary.
Note: The CLASS= keyword on the JOB statement is ignored for started task jobs.