Effective Reference Bit And Change Bit Recording
Original Publication Date: 1979-Mar-01
Included in the Prior Art Database: 2005-Feb-20
The illustrated circuit serves to improve virtual storage addressing in data processing systems comprising a main storage, subdivided into pages, and a key storage which stores a storage key for each page (P), a reference (R) bit and a change (C) bit. The reference and change bits serve to detect whether a page is being used. For storage accessing, i.e., for reading and writing, the reference bit has to be set to 1, whereas the change bit has to be set to 1 only when information is written into storage. For each storage access in such a data processing system, the corresponding word has to be read from key storage to effect the storage protection check and to provide the priority bits when the reference and change bits are subsequently written.