All requests sent to a CICS® region are handled by the CICS BAC request server, which runs as a standard CICS application program initiated by a CICS distributed program link (DPL) request using the external CICS interface (EXCI). Requests can originate in a CICS BAC communication server or a batch job step running the CICS BAC batch request utility. The updates to the CICS region control file are performed by the CICS BAC request server subtask, which is started by the CICS BAC startup procedure and then runs in the CICS address space as long as CICS BAC is active in the CICS region.