a) Explain what cache memory is used for and list 3 cache organizations. b) Suppose a computer has a 100 word memory and direct mapped cache with 10 blocks of 1 word each. For the following memory references (in sequence) state what cache block it maps to, and whether it is a hit or miss. Then draw the final contents of the cache indicating the tag fields in each block. Word addresses: 52, 37, 36, 22, 37, 46, 86, 22, 52, 46, 88, 43, 46, 52, 23 c) Explain the difference between a write-back and a write-through cache policy.