Any of many methods for controlling access to or use of memory. This control may be to prevent inadvertent user interference, to provide for system security, or both.

A mechanism for controlling the types of access permitted to an area of memory is known as a memory protect. In virtual memory systems it may be possible to assign certain areas as being capable of designated modes of access; for example, an area that is known to contain only the code of shared subroutines may be designated as having ‘execute only’ access, and can only be read during the instruction-fetch phase of executing an instruction. The permitted mode of access may differ for different processes. Definition of memory areas may use bounds registers; fixed memory areas may be controlled by locks and keys; individual words may be controlled by tags.

A violation of the memory protection system usually leads via an interrupt to a forced process termination.