Job Processing

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A job is a unit of work which can be made up of many job steps. job processing goes through a series of steps.


There are 6 phases in job processing:
1. Input
2.Conversion
3.Execution
4.Output
5.Hard copy
6.Purge

INPUT:

  • During this phases job is read from internal reader, terminal and card readers.
  • The Internal Reader is a special system program that is used by programs to submit jobs commands, and control statements to JES2 for processing.
  • JES2 will read the job stream and assign each job an ID, (Job Number). 
  • The job stream will then be Placed into special JES2 spool datasets ready for processing. JES2 will select jobs from the spool datasets for processing.

CONVERSION:
  • The JCL along with the PROC is converted into an interpreted text to be understand by JES and MVS. The text is stored into a dataset, which is called SPOOL.
  • At this stage the JCL syntax is checked for errors.If there are any errors then the job is queued for output processing  and no programs are run.
EXECUTION
  • In the Execution phase JES2 will receive request from MVS initiators for work to process.
  • JES2 selects a job and sends it to be processed by MVS.
  • An initiator is a special MVS system program which starts a job. Jobs are assigned to an initiator based on job classes.
  • Initiators are assigned one or more classes, if a job has the same job class as an initiator,
  • The initiator will build control blocks for the job and allocate the resources (files, tapes, etc) that you specified in the JCL.
  • The initiator will then begin executing the specified program.
OUTPUT:
  • In the output phase JES2 will handle processing of the output from your job. JES2 will check the outputclasses and device setup and queue the output for print or punch processing.
HARDCOPY:
  • In this phase the output is selected for processing. The output will be sent to the printer or punch device. Once the output has been processed the job is placed on the purge (delete) queue.
PURGE:
  • In the purge phase the space allocated on the spool datasets for your job and output is released (ie the output is deleted). Once the space is released, a message is issued to the system log to say that the output has been purged.

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