2377	 A Hardware Architecture for Implementing Protection Rings	 Protection of computations and information is an important aspect of a computer utility. In a system which uses segmentation as a memory addressing scheme protection can be achieved in part by associating concentric rings of decreasing access privilege with a computation. This paper describes hardware processor mechanisms for implementing these rings of protection. The mechanisms for implementing these rings of protection. The mechanisms allow cross-ring calls and subsequent returns to occur without trapping to the supervisor. Automatic hardware validation of references across ring boundaries is also performed. Thus a call by a user procedure to a protected subsystem including the supervisor is identical to a call to a companion user procedure. The mechanisms of passing and referencing arguments are the same in both cases as well. protection protection rings protection hardware access control hardware access control computer utility time-sharing shared information segmentation virtual memory Multics
