Synchronous cross memory communication, called cross memory, is both more complex and more flexible than scheduling an SRB. Cross memory requires the programmer to use MVS™ macros to establish a cross memory environment. This environment clearly defines the authorization requirements that protect the integrity of the address spaces involved. Once this environment is established, the application can use assembler instructions to transfer control from one address space to another.

Cross memory applications (as well as applications running in a single address space) can use the processor-managed linkage stack to simplify program linkages. In a cross memory environment, the program call (PC) instruction that transfers control to another routine can be either a basic PC or a stacking PC. If it is a stacking PC, the system saves status on the linkage stack before it passes control to the PC routine. When the PC routine returns control, the system automatically restores status from the linkage stack.

The key fact to remember, however, is that cross memory provides synchronous communication or processing across address spaces. When a task issues a PC instruction, control passes to the PC routine. When the PC routine completes, it returns control to the calling routine. Cross memory, for example, allows an application running in one address space to provide services for many users in other address spaces.