System interface protocol with optional module cache

Abstract

A computer system includes a plurality of processor modules coupled to a system bus with each of said processor modules including a processor interfaced to the system bus. The processor module has a backup cache memory and tag store. An index bus is coupled between the processor and the backup cache and backup cache tag store with said bus carrying only an index portion of a memory address to said backup cache and said tag store. A duplicate tag store is coupled to an interface with the duplicate tag memory including means for storing duplicate tag addresses and duplicate tag valid, shared and dirty bits. The duplicate tag store and the separate index bus provide higher performance from the processor by minimizing external interrupts to the processor to check on cache status and also allows other processors access to the processor's duplicate tag while the processor is processing other transactions.