JCL DD statements: Positional and frequently used parameters

In addition to its one positional parameter, the DD statement has well over 50 keyword parameters. But you'll most often use or encounter only this subset of these parameters.

A DD statement may contain only one positional parameter that must precede all keyword parameters. The following list describes the positional parameter values you may code for the DD statement.

* (an asterisk): The * parameter value begins an in-stream data set.
DATA: The DATA parameter value begins an in-stream data set that may contain statements with // in columns 1 and 2.
DUMMY: The DUMMY parameter value tells z/OS® not to perform any input, output, or disposition processing on the data set. Use the DUMMY parameter value when you are not providing input or do not want the output for a data set, or when testing a program.
DYNAM: The DYNAM parameter value is supported only to provide compatibility with previous versions of the z/OS operating system.

Even when you become a JCL expert, you probably will use only a handful of DD statement keywords frequently. Which keyword parameters you use depends on several factors, including whether you want to use an existing or create a new data set, what type of data set you are using or creating, and whether your company uses SMS to manage data sets. Here are the keyword parameters that you are most likely to use or see in existing JCL:

DCB

The DCB parameter defines the format type, length of records, and block size for a new data set.

DISP

The data set disposition parameter, DISP, indicates:

The current status of the data set, and whether the job requires exclusive use of it
How z/OS is to handle the data set after the job step ends either normally or abnormally.

The DISP parameters of DD statements help to prevent unwanted simultaneous access to data sets. In other words, the DISP parameter helps manage the integrity of data sets.

DSNAME or DSN

The DSNAME parameter, or its abbreviation DSN, specifies the actual name of the data set. z/OS uses this name to locate the data set in storage. The DSNAME or DSN keyword must be specified for an existing data set.

LABEL

The LABEL parameter specifies specific information about a tape or direct access data set, including:

The type and contents of the label or labels for the data set.
If a password is required to access the data set.
If the system is to open the data set only for input or output.
The expiration date or retention period for the data set.

SPACE

The SPACE parameter allocates storage for a new data set on a direct access storage device. The allocation of a data set means either or both of two things:

To set aside (or create) space for a new data set on a disk.
To establish a logical link between a job step and any data set.

SYSOUT

The SYSOUT parameter specifies a system output data set and its output class. A system output (SYSOUT) data set contains the job output that is to be printed. This job output is also known is the output stream. Unlike a permanent data set, a sysout data set is disk space that z/OS uses as buffer storage for processing output.

UNIT

When you are defining a new data set, you may use the UNIT parameter to tell z/OS to place the data set on:

A specific device, by specifying a hardware address.
A certain type or group of devices; examples of device types are 3390 for a disk or 3590 for tape.
The same device as another data set.

VOLUME or VOL

When you are defining a new data set, you may use the VOLUME parameter, or its abbreviation, VOL, to tell z/OS to place the data set on a specific volume. You can request:

A private volume
A specific volume by serial number
The same volume that another data set uses