Requesting amount and type of storage

The amount of space needed by a job or step can be specified in the REGION parameter of the JOB or EXEC statement. If REGION is on the JOB statement, each step of the job executes in the requested amount of space. If on the EXEC statements in a job, each step executes in its own amount of space. Use the EXEC statement REGION parameters when different steps need greatly different amounts of space.

The REGION parameter differs depending on whether the program uses virtual or central storage.

Region Size for Virtual Storage: When ADDRSPC=VIRT is coded or implied, the system establishes two values from the REGION parameter or the installation-defined default. These values are:

An upper boundary to limit region size for variable-length GETMAINs.
A second limiting value set by the IBM- or installation-supplied routine IEALIMIT or IEFUSI. The system uses this second value to limit:
- Fixed-length GETMAINs.
- Variable-length GETMAINs when the space remaining in the region is less than the requested minimum.
When the minimum requested length for a variable-length GETMAIN or the amount requested for a fixed-length GETMAIN exceeds this second value, the job or step abnormally terminates. See z/OS MVS Initialization and Tuning Guide and z/OS MVS Programming: Assembler Services Guide.

The amount of space requested must include the following:

Space for all programs to be executed.
All additional space the programs request with GETMAIN macro instructions during execution.
Enough unallocated space for task termination.

Region size for central (real) storage: When ADDRSPC=REAL is coded, the system establishes one value from the REGION parameter or the installation-defined default. The value is used as an upper boundary to limit region size for all GETMAINs.

The minimum region size must be:

8K if the program to be executed is reenterable and resides in an authorized library.
12K for all other programs.

Note that this is the minimum region for successful execution, but not necessarily the minimum region size for successful job completion. Programs executed in central storage should perform as much cleanup as possible before terminating.

Example 1:

//J28  JOB  ,'F. GOLAZESKI',CLASS=D
//S1   EXEC PGM=PROGREAL,REGION=20K,ADDRSPC=REAL
//DD1  DD   DSNAME=A.B.C,DISP=OLD
//S2   EXEC PGM=PROGVIRT,REGION=75K,ADDRSPC=VIRT
//DD2  DD   DSNAME=MYDS2,DISP=OLD

This example shows how to request storage for a program that must not be paged and for a program that can be paged. Step S1 executes in central (real) storage, without paging, while step S2 executes in virtual storage, with paging.

Example 2:

//STEPA  EXEC  PROC=MYPROC8,REGION.FIRST=750K,
//          REGION.SECOND=700K

This EXEC statement assigns space requests to two procedure steps, FIRST and SECOND, of a procedure named MYPROC8.

z/OS UNIX system services considerations: In z/OS UNIX System Services, callable service BPX1SRL lets a program modify its REGION size. Note that only superusers can increase their REGION size. See z/OS UNIX System Services Programming: Assembler Callable Services Reference for more information on the BPX1SRL callable service.