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Thursday, December 17, 2009

CPU Caching

The cache on your CPU has become a very important part of today's computing. The cache is a very high speed and very expensive piece of memory, which is used to speed up the memory retrieval process. Without the cache memory every time the CPU requested data it would send a request to the main memory which would then be sent back across the memory bus to the CPU. This is a slow process in computing terms. The idea of the cache is that this extremely fast memory would store and data that is frequently accessed and also if possible the data that is around it.

CPU's however use a 2 level cache system. The level 1 cache is the fastest and smallest memory, level 2 cache is larger and slightly slower but still smaller and faster than the main memory. The main problem with having too much cache memory is that the CPU will always check the cache memory before the main system memory.

Read cache is used to store copies of data and instructions that are retrieved from main memory or mass storage. If the central processing unit (CPU) needs to access the same data or instructions again, it can use the copy in read cache. This is much faster the going back to main memory or mass storage again. Write cache is a temporary store for data that needs to be written to main memory or mass storage. The CPU can move the data into cache very quickly, and then continue executing instructions. The data is subsequently moved to its permanent location by the cache controller, a process that takes more time because main memory and mass storage devices are much slower to access than cache memory.

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