The method used by MVS (OS/390) applications for linking to various operating system services. "Cross memory" means that the called routines reside in different address spaces than the calling program. They can even be in another computer. Rather than using a fixed address, cross memory services use a method of indirection whereby the calling program obtains a token that serves as a pointer to the actual routine. Cross memory services adds a more efficient approach than the supervisor call instruction that was initially the only method applications used to call the operating system.