JCL refresher#1: What is JCL

1.1 JOB CONTROL LANGUAGE consists of control statements that:

introduce a computer job to the operating system
request hardware devices
direct the operating system on what is to be done in terms of running applications and scheduling resources

JCL is not used to write computer programs. Instead it is most concerned with input/output— telling the operating system everything it needs to know about the input/output requirements. It provides the means of communicating between an application program and the operating system and computer hardware.

1.2 IS JCL DIFFICULT? … NOT NECESSARILY!

The role of JCL sounds complex and it is—JCL can be downright difficult.

JCL can be difficult because of the way it is used. A normal programming language, however difficult, soon becomes familiar through constant usage. This contrasts with JCL in which language features are used so infrequently that many never become familiar.

JCL can be difficult because of its design – JCL:

consists of individual parameters, each of which has an effect that may take pages to describe
has few defaults–must be told exactly what to do
requires specific placement of commas and blanks
is very unforgiving–one error may prevent execution

JCL is not necessarily difficult because most users only use a small set of similar JCL that never changes from job to job.

1.3 HOW DO YOU SEND INFORMATION TO THE COMPUTER?

BATCH PROCESSING VS. INTERACTIVE PROCESSING

Interactive Processing means that you give the computer a command and the computer responds to your command request. It is more like a conversation.

Batch Processing means that you give the computer a whole group of commands, usually in the form of some sort of program you have written, and have the computer process this group of commands. It is more like writing a letter.