Q. Describe Set-Associative Mapping?

A third type of cache organization known as set-associative mapping is an improvement on direct mapping organization in that every word of cache can store two or more words of memory under same index address. Every data word is stored together with its tag and number of tag data items in one word of cache is said to create a set. 

Let's consider an illustration of a set-associative cache organization for a set size of two as displayed in Figure below. Every index address refers to two data words as well as their associated tags. Every tag needs six bits and every data word has 12 bits so word length of cache is 2(6+12) = 36 bits. An index address of 9 bits can accommodate 512 words. So the size of cache memory is 512 × 36. Generally a Set-Associative cache of set size K will accommodate K-words of main memory in every word of cache.

Figure: Two-Way Set-Associative Mapping Cache