Editing Job Control Language (section)

===Jobs, steps and procedures===
For both DOS and OS the unit of work is the [[job stream|job]]. A job consists of one or several steps, each of which is a request to run one specific program. For example, before the days of [[relational database]]s, a job to produce a printed report for management might consist of the following steps: a user-written program to select the appropriate records and copy them to a temporary file; [[Sorting algorithm|sort]] the temporary file into the required order, usually using a general-purpose utility; a user-written program to present the information in a way that is easy for the end-users to read and includes other useful information such as sub-totals; and a user-written program to format selected pages of the end-user information for display on a monitor or terminal.

In both DOS and OS JCL the first "card" must be the JOB card, which:<ref>McQuillen, ''System/360–370 Assembler Language'', pp. 380–382.</ref> 
* Identifies the job.
* Usually provides information to enable the computer services department to bill the appropriate user department.
* Defines how the job as a whole is to be run, e.g. its priority relative to other jobs in the queue.

Procedures (commonly called ''procs'') are pre-written JCL for steps or groups of steps, inserted into a job. Both JCLs allow such procedures. Procs are used for repeating steps which are used several times in one job, or in several different jobs. They save programmer time and reduce the risk of errors. To run a procedure one simply includes in the JCL file a single "card" which copies the procedure from a specified file, and inserts it into the jobstream. Also, procs can include ''parameters'' to customize the procedure for each use.