Common service area (CSA/Extended CSA)

This area contains pageable and fixed data areas that are addressable by all active virtual storage address spaces. CSA normally contains data referenced by a number of system address spaces, enabling address spaces to communicate by referencing the same piece of CSA data.

CSA is allocated directly below the MLPA; extended CSA is allocated directly above the extended MLPA. If the virtual SQA space is depleted, the system will allocate additional SQA space from the CSA.

Specified by:

The SYSP parameter at the operator's console to specify an alternative system parameter list (IEASYSxx) that contains a CSA specification.
The CSA parameter at the operator's console during system initialization. This value overrides the current system parameter value for CSA that was established by IEASYS00 or IEASYSxx.

Note: If the size allocated for extended SQA is too small or is used up very quickly, the system attempts to steal space from extended CSA. When both extended SQA and extended CSA are used up, the system allocates space from SQA and CSA below 16 megabytes. The allocation of this storage could eventually lead to a system failure. Ensuring the appropriate size of extended SQA and extended CSA storage is critical to the long-term operation of the system.