Module 2: JCL Structure and Job Card
JCL- What is it?
Language used for Controlled execution of Jobs in a system. It is interface between program and MVS operating system.
Job Entry Subsystem (JES)
JES is subsystem of OS/390 and MVS mainframe. Once you are ready with creation of Job, it should be submitted to JES with use of SUB or SUBMIT command. JES is the job processor of MVS operating system. IBM provides two kinds of job entry subsystems namely JES2 and JES3. JES is responsible for prioritization, scheduling and execution of the submitted jobs.
Below table specifies basic differences between JES2 and JES3
|Multiprocessor or Decentralized environment wherein each processor independently deals with incoming job||JES3 is centralized environment. Using a common JOB queue and centralized control over the local processors, JES3 Subsystem distributes the job inputs to them.|
|Allocation of datasets required by a step are done only just before the step executes.||Allocates datasets for all the steps before the job is scheduled|
|Control statements starts with /*||Control statements starts with //*|