Emulated target associative memory system with a multi-digit incrementable validity counter

Abstract

A host computer system, including an addressable main memory storing data pages and a page table, emulates a target computer system which includes an emulated target central processing unit, an emulated target associative memory and an emulated target multi-digit incrementable validity counter. The target associative memory stores a plurality of entries in accordance with a low order virtual address component issued by the target processor when access to a given page in main memory is sought. Each entry in the target associative memory includes fields respectively holding: 1) a high order virtual address component; 2) a real page address; and 3) a multi-digit validity count. The target multi-digit counter stores a current validity count. When access to a data page is sought, comparisons are made: 1) between the high order virtual address component of the data page and the high order virtual address component read from the target associative memory entry; and 2) between the multi-digit validity count read from the target associative memory entry and the multi-digit current validity count in the target counter. If there is a full match, the real page address of the requested page is read from the target associative memory entry. If there is not a match, the page table is consulted to obtain the real address of the requested page, and the target associative memory is updated accordingly.