Job Steps: You enter a program into the operating system as a job step. A job step consists of the job control statements that request and control execution of a program and request the resources needed to run the program. A job step is identified by an EXEC statement. The job step can also contain data needed by the program. The operating system distinguishes job control statements from data by the contents of the records.

Jobs: A job is a collection of related job steps. A job is identified by a JOB statement.

Input Streams: Jobs placed in a series and entered through one input device form an input stream. The operating system reads an input stream into the computer from an input/output (I/O) device or an internal reader. The input device can be a card reader, a magnetic tape device, a terminal, or a direct access device. An internal reader is a buffer that is read from a program into the system as though it were an input stream.

Cataloged and In-Stream Procedures: You often use the same set of job control statements repeatedly with little or no change, for example, to compile, assemble, link-edit, and execute a program. To save time and prevent errors, you can prepare sets of job control statements and place, or catalog, them in a partitioned data set (PDS) or partitioned data set extended (PDSE) known as a procedure library. The data set attributes of a procedure library should match SYS1.PROCLIB (record length of 80 and record format of FB). Such a set of job control statements in the system procedure library, SYS1.PROCLIB (or an installation-defined procedure library), is called a cataloged procedure.

To test a procedure before placing it in the catalog, place it in an input stream and execute it; a procedure in an input stream is called an in-stream procedure. The maximum number of in-stream procedures you can code in any job is 15.

Steps in a Job: A job can be simple or complex; it can consist of one step or of many steps that call many in-stream and cataloged procedures. A job can consist of up to 255 job steps, including all steps in any procedures that the job calls. Specification of a greater number of steps produces a JCL error.