Importance

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Abstract

A cached multiprocessor system operated in an ordered pipeline timing sequence in which the time slot for use of the cache is made long enough to permit only one cache access. Further, the time slot for data transfers to and from the processors succeeds the time slot for accessing the cache. The sequence is optimized for transactions that require only one cache access, e.g., read operations that hit the cacgenerally require a second cache access in order to update or allocate the cache. These transactions are entered into a queue with order preserved prior to permitting a second access to the cache. Also, a duplicate tag store is associated with the queue and maintained as a copy of the tag store in the cache. Whenever a cache tag is to be changed, a duplicate tag in the duplicate tag store is changed prior to changing the cache tag. The duplicate tag store thus always provides an accurate indication of the contents of the cache. The duplicate tag store is used to determine whether a second access to the cache for an update is necessary.

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First Claim