Determining whether to use a started task - IBM-JCL

When you determine where and when you want a set of JCL to run, you will consider using batch jobs or started tasks. Batch jobs are scheduled by a job entry subsystem (JES) and are scheduled to run based on the resources they require and their availability, or based on controls you put on the batch system. Controlling where and when a batch job runs is more complex than using a started task. A started task is a set of JCL that is run immediately as the result of a START command. Started tasks are generally used for critical applications. The advantages to using started tasks are:

  • You can control where and when your set of JCL is run. For example, you can have the set of JCL started at each IPL of the system.
  • You can specify both static system symbols and JCL symbols in the JCL. Static system symbols and JCL symbols provide additional control over JCL that is used on different systems. For example:
  • –When access to production data sets is controlled to protect critical business data, you can specify symbols that represent test data sets. After testing the data sets, you can change the values of the symbols to represent production data sets without changing the source JCL.
    –When you need to swap in an older level of a subsystem while diagnosing problems with a newer level, you can change the values of symbols to represent the older subsystem without changing the source JCL.

For more information about system symbols and JCL symbols.

Note: In the past, some users set up batch jobs that controlled their programs. Users allocated a PDS, added JOB JCL to a member of the PDS, and then read the PDS member into an internal reader; these actions initiated a batch job for the started task. While this method afforded some advantages, it did not allow for symbolic support.


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