CICS main storage areas

CICS® maintains and manages storage by allocating one or more dynamic storage areas at initialization.

Individual DSA size is not fixed. Individual DSA size varies according to demand as CICS allocates new extents for or removes extents from the DSA.

CICS manages dynamic storage as two pools, one above the 16M boundary, and one below. The maximum size of these pools is limited by the values specified on the DSALIM and the EDSALIM SIT parameters respectively.

The CICS subsystem storage protection feature helps to protect CICS storage from being overwritten by applications. CICS provides this function by dividing storage into three key types. These are the key storage types:
READ ONLY
Used to load reentrant programs and cannot be modified (provided reentrant storage protection has been selected in the SIT through the RENTPGM keyword).
USER
User key storage, which is used by applications and is not protected.
CICS
CICS key storage, which is used for CICS and cannot be overwritten by applications running in user key (provided subsystem storage protection has been selected in the SIT through STGPROT and the hardware supports system storage protection).
CICS manages storage for each of the three keys using different DSAs. In CICS Transaction Server on z/OS, there are nine dynamic storage areas. These are the dynamic storage areas:
  • The user DSA (UDSA)
  • The read only DSA (RDSA)
  • The shared DSA (SDSA)
  • The CICS DSA (CDSA)
  • The extended user DSA (EUDSA)
  • The extended read only DSA (ERDSA)
  • The extended shared DSA (ESDSA)
  • The extended CICS DSA (ECDSA)
  • The above the bar CICS DSA (GCDSA)