Batch jobs are selected for execution by initiators, each one running in a separate address space. Initiators are controlled by JES2 or by the workload manager (WLM). Who controls the initiators is determined by the job class and by the MODE= parameter (JES or WLM) in the JOBCLASS statement. JES2 maintains two different queue organizations for all jobs awaiting execution to service the two different selection mechanisms:

1. All jobs are queued by job class, priority, and the order in which they finished conversion. This is the queue from which JES2 managed initiators select jobs for execution.
2. Jobs awaiting execution in WLM managed job classes are also queued by their WLM assigned service class in the order they were made available for execution. This is the queue from which WLM managed initiators select jobs for execution.