To store and retrieve subsystem-specific information, you can use the IEFSSI macro. A subsystem or a subsystem initialization routine needs to be able to pass information to the subsystem's function routines. If the subsystem code and its function routines are in separate load modules or run in separate address spaces, there may be no direct way for the subsystem to communicate with its function routines. The store and retrieve services provide a way for subsystems to store and retrieve subsystem-specific information and pass that information between subsystem components.