What is JCL Mainframe?
One IBM manual compares a set of JCL statements to a menu order in a restaurant. The whole order is comparable to the job. Back in the kitchen, the chefs divide the order up and work on individual dishes (job steps). As the job steps complete, the meal is served (but it has to be served in the order prescribed just as some job steps depend on other job steps being performed first).
JCL statements mainly specify the input data sets (files) that must be accessed, the output data set to be created or updated, what resources must be allocated for the job, and the programs that are to run, using these input and output data sets. A set of JCL statements for a job is itself stored as a data set and can be started interactively. MVS and OS/390 provide an interactive menu-like interface, ISPF, for initiating and managing jobs.
In MVS and OS/390, the part of the operating system that handles JCL is called the Job Entry Subsystem (JES). There are two versions, JES2 and a later version with additional capabilities, JES3.
JCL uses a number of IBM utility programs to assist in the processing of data. Utilities are most useful in batch processing. The utilities can be grouped into three sets: (1) Data Set Utilities – to create print, copy, move and delete data sets; (2) System Utilities – to maintain and manage catalogs; (3) Access Method Services – to process VSAM (Virtual storage access method) and non-VSAM data sets.
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