DSAs in 24-bit storage: CDSA, UDSA, SDSA, and RDSA

The CICS dynamic storage areas (DSAs) below the line (below 16 MB) are in 24-bit storage. These storage areas do not have a collective name. The CICS system initialization parameter DSALIM specifies the limit on the total size of these dynamic storage areas.

The amount of storage specified by the DSALIM value is allocated as guaranteed storage at system initialization. Within this storage, CICS® manages the following dynamic storage areas automatically, and you do not need to specify their individual sizes:

CDSA (CICS DSA)

The storage area for all non-reentrant CICS-key RMODE(24) programs, all CICS-key task-lifetime storage in 24-bit storage, and for CICS control blocks that reside in 24-bit storage. The CDSA is always allocated from CICS-key storage.

UDSA (User DSA)

The storage area for all user-key task-lifetime storage in 24-bit storage. If you specify the system initialization parameter STGPROT=YES for the CICS region, which is the default, the UDSA is allocated from user-key storage. If you specify STGPROT=NO, the UDSA is allocated from CICS-key storage.

SDSA (Shared DSA)

The storage area for any non-reentrant user-key RMODE(24) programs, and also for any storage obtained by programs issuing CICS GETMAIN commands for 24-bit storage with the SHARED option. If you specify the system initialization parameter STGPROT=YES for the CICS region, which is the default, the SDSA is allocated from user-key storage. If you specify STGPROT=NO, the SDSA is allocated from CICS-key storage.

RDSA (Read-only DSA)

The storage area for all reentrant programs and tables in 24-bit storage. If you specify the system initialization parameter RENTPGM=PROTECT for the CICS region, which is the default, the RDSA is allocated from read-only key-0 protected storage. If you specify RENTPGM=NOPROTECT, the RDSA is allocated from CICS-key storage.