HP Vectra XU 6/XXX HP Vectra XU - Guide to Optimizing Performance, Not Orderab - Page 61

2 Technical Reference The Intel Pentium Pro Processor Dedicated Level-Two Cache Bus The Pentium Pro increases the performance of its level-two cache by accessing it over a dedicated, 64-bit internal bus. This means that accesses to the cache will cause no contention with any operations on the local bus. It also ensures that the level-two cache is able to operate at the full internal clock speed of the processor. Level-two cache bus Level-two cache Processor core Local bus Cache Coherency One important implication of using cache memories is that duplicate copies of data exist in different parts of your PC. With duplicate copies of the same data, a mechanism must be used to ensure coherency between the copies. This is particularly true for dual processor configurations, where duplications can exist not only between a processor cache and memory, but also between the caches in the two processors. The Pentium Pro's level-two data cache is a copy-back cache, meaning that if the processor writes data that produces a cache hit, then that data will be written directly in the level-two cache. The cache will then copy the data back to memory at a later time. Until the cache copies the data back to memory, the copy of the data held in memory is no longer valid. English 55