Cache Memory

It is the smallest and the fastest memory which stores copies of data from most frequently used main memory locations. It is very near to Processor or even in the Processor. The main idea behind the use of Cache memory is to reduce average time to access memory. Its speed approaches to the speed of CPU components.

Operation: -Whenever CPU wants to access the main memory, it first looks the Cache Memory. If the word is found in the Cache then it is read from there. But if the word is not found in Cache it is read from the main memory. Block of word that is read from main memory is transferred to cache memory .Only those words are kept in Cache that are most frequently used.

Whenever CPU finds a word in Cache it is called a hit and if the word is not found in the cache it is called Miss. The performance of Cache is measured in terms of hit ratio. The ratio of number of hits (all hits + all Miss) is divided by the number of CPU references to memory to obtain hit ratio. The Process of transforming words from main memory to Cache is called Mapping.

Fast access time is the main characteristics of Cache Memory. Hence no or little time should be wasted when searching for a word in cache.