Memory Protection in Multiprocessing Systems

In a multiprocessor system where a bank of processors share a bank of memories, it becomes necessary to equip a processor with the capability to periodically deny to other processors access to certain memory locations. We call this the memory-protection problem because the processor which has gained access to the data must protect it from others. The type of data contained in the memory locations to be protected dictates the characteristics of the protection techniques which are applicable. This paper outlines the techniques as they apply to four classes of data which are defined for multiprocessor systems. In those cases where special hardware is required, such hardware is described. Furthermore, the programming implications and the error control problems are discussed.