Yi-Ning-Cache Memory.ppt

Cache Memory Yi-Ning Huang Principle of Locality A phenomenon that the recent used memory location is more likely to be used again soon. What is cache memory? According to locality principle, Scientists designed cache memory to make memory more efficient. Cache contains the information most frequently needed by the processor. Cache memory is a small but fast memory module inserted between the processor and the main memory. Example of grocery shopping If you buy one single item you need immediately in the grocery store. Then you might have to go to grocery store again soon. It is waste of time and waste of gas ( suppose you drive to grocery store) Example of grocery shopping Most of people will do: You buy any items you need immediately and additional items you will most likely need in the future. Example of grocery shopping Grocery store is similar to main memory Your home is similar to cache. To speed up access time, cache would stores information the computer will need immediately and will most likely need in the future. What is cache memory? According to locality principle, Scientists designed cache memory to make memory more efficient. Cache contains the information most frequently needed by the processor. Cache memory is a small but fast memory module inserted between the processor and the main memory. 3 general functions in cache Address translation function Address mapping function Replacement algorithm Mapping Cache Determines where the blocks are to be located in the cache. 3 types of mapping Fully associative mapping Direct mapping Set associative mapping Mapping Cache: Direct mapping Each primary memory address maps to a unique cache block. If cache has N blocks, then block address X of main memory maps to cache block Y = X mod N ( Cache block = block address mod number of blocks) Mapping Cache: Direct mapping Mapping Cache: Direct mapping Mapping Cache: Direct mapping Use least significant b bits of the tag to indicate the ca