There are several important points to remember about cross memory communication:

1. Cross memory facilities enable the service provider to provide services to some or all users.
2. The service provider code and the user code can execute in the same address space or in different address spaces.
3. The service provider uses MVS™ macros to establish and maintain the environment needed for cross memory communications.
4. The service provider supplies services through PC routines. For each PC routine, the service provider supplies the user with a PC number that identifies the routine.
5. To obtain a service from the service provider, the user issues a PC instruction. The instruction specifies the PC number of the PC routine that the user wants to invoke.
6. The stacking PC provides more capability and better performance than does the basic PC. IBM® recommends using the stacking PC.
7. To store data into or retrieve data from other address spaces or from data spaces, IBM recommends using ARs. The service provider can, if necessary, access data in the user's address space without using ARs. To do this, the service provider can use the MVCP instruction to retrieve data from the user's address space and the MVCS instruction to move data into the user's address space.