Wikipedia:Today's featured article/January 7, 2005

A CPU cache is a cache used by the central processing unit of a computer to reduce the average time to access memory. The cache is a smaller, faster memory which stores copies of the most frequently used main memory locations. So long as most accesses are to the cached copies, the average latency to memory will be closer to the cache latency than to the latency of main memory. When the processor wishes to read or write a location in main memory, it first checks the main memory address against the tags in the cache. If one of the tag entries matches (a cache hit), the processor reads or writes the corresponding data in that entry rather than doing the same to main memory. If none of the tag entries match, the reference is a miss. Misses are slow because they require the data from main memory, and the slowness of that memory is, of course, the reason for the cache in the first place. The proportion of accesses that result in a cache hit is known as the hit rate. (more...)

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