ALLOCxx (allocation system defaults)

Use the ALLOCxx member of SYS1.PARMLIB to define installation defaults for:

Unit names (dynamic allocation, unit-affinity-ignored, and redirection from TAPE)
Space attributes
TIOT size
Handling allocation requests
Catalog error policies.

These installation defaults for handling allocation requests can be overridden by installation exit routines specified in the EXITxx parmlib member. For information about the allocation exit routines, see z/OS MVS Installation Exits. After IPL, use the SETALLOC command to change any of the defaults (except for 2DGT_EXPDT).