The processor operates in one of two modes of privilege: the "Supervisor" mode and the "User" mode. The privilege mode determines:
* which instructions are legal:** User programs are not permitted to execute the stop instruction or the reset instruction.** To ensure that a user program cannot enter the Supervisor State except in a controlled manner, the instructions which modify the whole State register are privileged.** To aid in debugging programs which are to be used as Operating Systems, the move to user Stack pointer (MOVE to USP) and move from user Stack pointer (MOVE from USP) instructions are also privileged.
* select between the Supervisor Stack Pointer (SSP) and the User Stack Pointer (USP) in instruction references
* and may by used by an external Memory Management Unit (MMU) to control and translate memory accesses