Choosing the access method for MRO

You can specify ACCESSMETHOD(XM) to select MVS™ cross-memory services for an MRO link. Cross-memory services are used only if the other end of the link also specifies cross-memory.

When you specify ACCESSMETHOD(XM) in a connection definition, a region containing this definition uses one of the 512 available MRO XM logons for the LPAR. A region can contain both ACCESSMETHOD(XM) and ACCESSMETHOD(IRC) connections, but if the region contains one or more XM connections then the region uses an MRO XM logon.

To select the CICS Type 3 SVC for interregion communication, use ACCESSMETHOD(IRC).

The use of MVS cross-memory services reduces the number of instructions necessary to transmit messages between regions. Also, less virtual storage is required in the MVS common service area. However, cross-memory services can be less attractive from the security point of view (see Implementing MRO security).

Cross-memory services also require CICS address spaces to be nonswappable. For low-activity systems that would otherwise be eligible for address space swapping, you might prefer to accept the greater path length of the CICS interregion SVC rather than the greater real storage requirements of nonswappable address spaces.