The DD statement consists of the characters // in columns 1 and
2 and four fields: name, operation (DD), parameter, and comments.
Do not code comments if the parameter field is blank.
A DD statement is required for each data set.
The maximum number of DD statements per job step is 3273, based on the number of single DD
statements allowed for a TIOT (task input output table) control block size of 64K. This limit can be
different depending on the installation-defined TIOT size. The IBM-supplied default TIOT size is
32K. For information about changing the size of the TIOT, see the ALLOCxx parmlib member information
in z/OS MVS Initialization and Tuning Reference. For
information about how dynamic allocation might cause changes to the task input/output table (TIOT),
see z/OS MVS Programming: Authorized Assembler Services Guide.
In a JES3 system, the installation might further reduce the maximum number of DD statements per
job.