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z/OS uses a job entry subsystem or JES to receive jobs into the operating system, to schedule them for processing by z/OS, and to control their output processing. JES is the component of the operating system that provides supplementary job management, data management, and task management functions such as scheduling, control of job flow, and the reading and writing of input and output streams on auxiliary storage devices, concurrently with job execution (a process called spooling).

z/OS manages work as tasks and subtasks. Both transactions and batch jobs are associated with an internal task queue that is managed on a priority basis. JES is a component of z/OS that works on the front end of program execution to prepare work to be executed. JES is also active on the back end of program execution to help clean up after work is performed. This includes managing the printing of output generated by active programs.

JES2 is a z/OS Base element. JES2 accepts the submission of work for the BCP and exercises independent control over its job processing.

JES2 PDF files z/OS V1R8.0

JES2 compared to JES3

IBM provides two kinds of job entry subsystems: JES2 and JES3. In many cases, JES2 and JES3 perform similar functions: they read jobs into the system, convert them to internal machine-readable form, select them for processing, process their output, and purge them from the system.

In a mainframe installation that has only one processor, JES3 provides tape setup, dependent job control, and deadline scheduling for users of the system, while JES2 in the same system would require its users to manage these activities through other means. In an installation with a multi-processor configuration, there are noticeable differences between the two, mainly in how JES2 exercises independent control over its job processing functions. That is, within the configuration, each JES2 processor controls its own job input, job scheduling, and job output processing. Most installations use JES2, as do the examples in this text.

JES3

JES3 Priced optional feature JES3 accepts the submission of work for the BCP and exercises centralized control over its job processing.

JES3 PDF files z/OS V1R8.0