4. In a computer system, the memory has 16 blocks and the cache has 4 blocks. Assume there is only one word per block with 4 bytes in one word. The reference sequence in terms of word location is: 2, 4, 7, 8, 1, 9, 4, 14, 2, 8, 2. (a) [7%] How many bits are there for the index and the tag if this is a direct-mapped cache, fully associative cache, and 2-way set associative cache, respectively? (b) [7%] If the cache is a direct-mapped cache, how many misses do we have if the cache is initially empty? Give the hit or miss sequence for each reference. (c) [7%] If the cache is a fully associative cache, how many misses do we have with LRU replacement policy if the cache is initially empty? Give the hit or miss sequence for each reference. (d) [7%] If the cache is a two-way set associative cache, how many misses do we have with LRU replacement policy if the cache is initially empty? Give the hit or miss sequence for each reference.