This form of mapping is an enhanced form of direct mapping where the drawbacks of direct mapping are removed. Set associative addresses the problem of possible thrashing in the direct mapping method. It does this by saying that instead of having exactly one line that a block can map to in the cache, we will group a few lines together creating a set. Then a block in memory can map to any one of the lines of a specific set..Set-associative mapping allows that each word that is present in the cache can have two or more words in the main memory for the same index address. Set associative cache mapping combines the best of direct and associative cache mapping techniques.
In this case, the cache consists of a number of sets, each of which consists of a number of lines. The relationships are
m = v * k
i= j mod v
where
i=cache set number
j=main memory block number
v=number of sets
m=number of lines in the cache number of sets
k=number of lines in each set
