JES ( Job Entry Subsystem )

JES takes care of execution of job. When the job is submitted, it will allocate space for execution.

JES3

• Allocates datasets to all the steps before the job is scheduled.
• Centralized environment.
• This will release the resource only after completion of all the steps and no other program can access that resource until the completion of execution.

JES2

• Allocates datasets required by a step just before the step executes.
• Decentralized environment.
• This releases the resource after completion of every step and that resource can be used by another program.