Discussion
Cache memory is used in a computer because it
Answer: A
Correct answer: is faster than main memory and holds recently used data
Cache is a small, very fast memory placed between the processor and main memory, holding copies of data and instructions that have recently been used or are likely to be used next. It works because of the principle of locality. Temporal locality means a location just accessed is likely to be accessed again soon; spatial locality means nearby locations are likely to be accessed next, which is why data is fetched in whole cache lines rather than single bytes. A request found in cache is a hit and is served in a few processor cycles; a miss requires main memory and costs hundreds. Because hit rates in practice exceed 90 per cent, the average access time approaches that of the cache. It is built from SRAM, which uses a flip-flop per bit and needs no refreshing, unlike the DRAM of main memory - faster but far more expensive per bit, which is why cache is small. Modern processors use several levels, L1 through L3.
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