Fig. 10. A protection system using access controllers containing access control lists. In this system, every segment has a single corresponding access controller with its own unique identifier for addressing purposes; pointer registers always contain the unique identifiers of access controllers. Program A is in control of the processor, and it has already acquired a pointer to the library catalog. Since the access control list in the access controller for the library catalog contains Doe's name, the processor can use the catalog to find the pointer for the shared math routine. Since his name also appears in the access control list of the math routine, the processor will then be able to use the shared math routine.