Cross memory communication in mvs

There is 2 ways to call service provided by another address space. 

Asynchronous cross memory communication is via SRB. For example, VTAM schedule a SRB to the address space waiting for the terminal data when it arrives  

Synchronous cross memory is via PC call.  Service provider is responsible to save the registers and status of the caller in the processor provided linkage stack, and restore them before returning (called stacking PC). Service provider set up the environment using macros and created a PC number for the caller to call.