1. A computer operating system security mechanism including a non-penetrable hardware storage means for storing special privileged instruction identification data for each privileged instruction which it is desired to protect, means for loading said special identification data in said storage means and said non-penetrable storage means being loadable only during the initial program load time of the system, means for recognizing privileged instructions which are presented to the system for execution, means for determining if a privileged instruction presented to the system for execution has proper identification data associated therewith, prior to execution of said privileged instruction, said last named means comprising comparison means for accessing said non-penetrable storage means associated with said privileged instruction and the identification data stored therein.