JES2 control of batch job initiation

After conversion of a job's JCL, JES2 places the job into an appropriate class queue to await execution. If the job class is a JES2 managed class (JOBCLASS MODE=JES), then JES2 initiators select a job from the class queue (depending on the job's priority) and pass control to MVS™ to execute your program. If the job class is a WLM managed class (JOBCLASS MODE=WLM), see WLM control of batch job initiation.

During execution, the initiator selects non-held jobs in priority order within their class, and the non-held classes in the order specified for that initiator. That is, the JES2 initiator selects the lowest priority job in the first non-empty class ahead of the highest priority job of the next class. Exceptions to these selection criteria are explained above and include:
  • Held Jobs (TYPRUN=HOLD, JCLHOLD, or operator hold)
  • Held Classes
  • Held Execution Environment ($P XEQ)
  • Member Affinity (SYSAFF)
  • Scheduling Environment
  • Duplicate Job Name
With the introduction of 2-8 character job class names in z/OS 2.1, the syntax for specifying an initiator class list has changed. For MAS members running z/OS 1.x, the class definition and initiator syntax remains: 
CLASS=ABCDE       - $D I(*), CLASS=A   WILL NOT MATCH
For MAS members running z/OS 2.1 or later, the class definition and initiator syntax is: 
CLASS=(A,B,C,D,E) - $D I(*), CLASS=(A) WILL MATCH

In addition to listing job class names, you can initiate batch jobs using job class group names. When you initiate a job class group, there is no processing priority given to any of the job classes within the group; job classes within the group are processed in a round robin fashion.