Fastest memory in your PC..

Cache memory(read as “cash” and not “ache”) holds frequently used instructions/data which the processor may require next and it is faster access memory than RAM, since it is on the same chip as the processor. Cache Memory is a special very high-speed memory. It is used to speed up and synchronizing with high-speed CPU. It lies in the path between the processor and the memory. The cache memory therefore, has lesser access time than memory and is faster than the main memory .

It acts as a high speed buffer between CPU and main memory and is used to temporary store very active data and action during processing since the cache memory is faster then main memory, the processing speed is increased by making the data and instructions needed in current processing available in cache.This reduces the need for frequent slower memory retrievals from main memory, which may otherwise keep the CPU waiting.The cache memory is very expensive and hence is limited in capacity.

Cache Performance

The performance of the cache depends on the cache hits and the cache misses, which are the factors that create constraints to the performance of the system.

When the processor needs to read or write a location in main memory, it first checks for a corresponding entry in the cache.Cache hits are the number of accesses to the cache that actually find that data in the cache, whereas Cache misses are those that do not find the block in the cache. For a cache miss, the cache allocates a new entry and copies in data from main memory, then the request is fulfilled from the contents of the cache.

These cache hits and misses contribute to the term Average Access Time (AAT) also known as AMAT (Average Memory Access Time) which, as the name suggests, is the average time it takes to access the memory.The performance of cache memory is frequently measured in terms of a quantity called Hit ratio.

Hit ratio = hit / (hit + miss) = no. of hits/total accesses