oEach entry also has a Diagramwhich memory cache tag, of a CPUspecifies the identity of the datum inthe backing store of which the entry isa copy.oWhen the cache client needs toaccess a datum presumed to exist inthe backing store, it first checks thecache.oIf an entry can be found with a tagmatching that of the desired datum,the datum in the entry is usedinstead. cacheoThe percentage of accesses that Diagram of a CPU memoryresult in cache hits is known as cache memory cachethe hit rate or hit ratio of the cache.percentage of accesses that result in cache hits is known as the hit rate or hit ratio of the cache.
When a system writes a datum to cache, it must at some point write that datum to backing store as well. The timing of this write is controlled by what is known as the write policy.There are two basic writing approaches: Write-through - Write is done synchronously both to the cache and to the backing store. Write-back- Writing is done only to the cache. A modified cache block is written back to the store, just before it is replaced.
More expensiveConsumes more power Low density