CLASS Parameter in JCL is used to categorize the JOBs that runs in one OS installation. During installation itself all Class parameters are defined and assigned with specific attributes. These attributes decides whether or how to run a JOB.
As we know all the JOBS submitted runs in an Initiator address space and every class is assigned with one or more Initiators during the installation. So depending on the duration and/or number of resources required for a JOB, Class is assigned to different jobs. Generally test environments are given a set of CLASS parameter values and PROD environment are given different set of values.
This is a KEYWORD parameter and is optional to code. When it is not given , OS assigns a default Class for that JOB. This parameter helps to balance the load of JOBS that are executing in an environment. It also helps in prioritizing the JOB execution.System considers PRTY parameter along with CLASS to decide the JOB priority.
Few jobs needs to be given higher priority while other jobs may not require any priority while running the jobs. And in some cases, jobs can be put on HOLD.
It means class parameter tells the system that this JOB is of this Class, so that depending on this system knows that this jobs takes longer time/shorter time & resources required so the system assigns the resources accordingly.
A to Z and 0 to 9
Where to code
This can be given in the JOB card.
//CUSTRPT JOB (0022),’cUSTOMER RPT’,CLASS=A,MSGLEVEL=1,