Storage Keys Addressed by Logical or Physical Address Bus Under Program Control in IBM System/370
Original Publication Date: 1988-Nov-01
Included in the Prior Art Database: 2005-Feb-15
In IBM System/370 architecture there are four storage key bits assigned for protection of main storage from destruction and misuse caused by erroneous or unauthorized storing or fetching by a program. A key value in the user program status word (PSW) is compared against the key stored in an array on every main store access, and when a miscompare occurs, the access is blocked and notified to the supervisor program by an exception. Normally, the key array is addressed by the physical address bus, i.e., the translated address bus when dynamic address translation (DAT) is on. However, there are some multi-user operating systems that would require these storage keys on logical bus for various reasons.