XMEMOPT parameter

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Cross-memory PC options


Default value
X'02' if M204XSVC is linked into the nucleus (as of V7.5, M204XSVC is linked into the nucleus by default)
X'00' if M204XSVC is not linked into the nucleus
Parameter type
Where set
On User 0's parameter line
Related products
Model 204 V2.1 or earlier


This parameter sets the Model 204 cross-memory services options that can be invoked during execution of Model 204.

This parameter applies only to z/OS.

Prior to Model 204 7.5, nonzero settings of XMEMOPT enabled features whose execution was accomplished with a system supervisor call (SVC), and the SVC number was specified as the XMEMSVC parameter value in the Model 204 CCAIN. Under the default installation of Model 204 as of version 7.5, the M204XSVC module is not installed as an SVC, and specifying an XMEMSVC value is not necessarily required for the XMEMOPT features.

Valid settings of XMEMOPT are:

X'80' Activates CRAM-XDM.

If the Online and CRAM-XDM load modules are not APF authorized, the X'80' bit is turned off.

X'20' Use SUSPEND/RESUME instead of WAIT/POST for communication between Model 204 real subtasks. This option may reduce operating system overhead slightly.

If the Online load module is not APF authorized, the X'20' bit is turned off.

X'04' Forces initialization of cross-memory environment (M204XSVC).

This bit might be useful for the UL/DB2 feature.

X'03' Invokes both Timer PC and IOS Branch Entry.
X'02' Invokes IOS Branch Entry (recommended for z/OS) to handle all database and CCATEMP I/O.
X'01' Invokes Timer PC.

Note: As described in the Timer PC section, this bit is automatically turned off as of version 7.4 of Model 204 if your system supports the ECTG instruction.

X'00' Disables Model 204 cross-memory services.

Note: VIO is incompatible with IOS Branch Entry and EXCPVR.