DSAs in 64-bit storage: GCDSA, GUDSA, and GSDSA
CICS® dynamic storage areas above the bar are collectively called the above-the-bar dynamic storage area (GDSA). This storage is 64-bit storage. The z/OS® MEMLIMIT parameter limits the 64-bit storage in the CICS region, including the GDSA.
The MEMLIMIT value that the z/OS operating system assigns to the CICS address space controls the upper limit for 64-bit storage in the CICS region. This 64-bit storage includes both the GDSA, and MVS™ storage in the CICS region outside the GDSA.
In contrast, the 24-bit storage specified by the DSALIM value and the 31-bit storage specified by the EDSALIM value relate only to the CICS DSAs.
The GDSA does not preallocate an amount of guaranteed storage.
The GDSA contains the following dynamic storage areas:
- GCDSA (above-the-bar CICS DSA)
- The storage area for all CICS-key task-lifetime storage in 64-bit (above-the-bar) storage, and for CICS facilities that use 64-bit storage. See CICS facilities that use 64-bit storage. The GCDSA is always allocated from CICS-key storage.
- GUDSA (above-the-bar user DSA)
- The storage area for all user-key task-lifetime storage in 64-bit (above-the-bar) storage. If you specify the system initialization parameter STGPROT=YES for the CICS region, which is the default, the GUDSA is allocated from user-key storage. If you specify STGPROT=NO, the GUDSA is allocated from CICS-key storage.
- GSDSA (above-the-bar shared DSA)
- The storage area for any storage that programs obtain by issuing a EXEC CICS GETMAIN64 command to obtain 64-bit storage with the SHARED option. If you specify the system initialization parameter STGPROT=YES for the CICS region, which is the default, the GSDSA is allocated from user-key storage. If you specify STGPROT=NO, the GSDSA is allocated from CICS-key storage.