(a) In the memory hierarchy design, cache performance is measured by the average cache memory access time, which can be expressed in terms of hit time, miss rate and miss penalty as Average cache memory access time = hit time + miss rate x miss penalty Present two methods for each factor in the right side of the above formula to reduce cache access time, and briefly explain these methods. (6 marks) (b) A memory system is revised by introducing a cache, which operates at a 20% cache miss rate for both instruction and data references. The cache miss penalty is 10 clock cycles, and memory references per instruction are 1.5. The perfect CPI is 1 clock cycle. Calculate the performance improvement introduced by the cache, using the CPU time that accounts for the number of clock cycles waiting for a memory access. Show all workings and state any assumptions you make. (8 marks) (c) In a computer, virtual memory in the memory hierarchy physically resides on a rotating magnetic disk (hard disk). Describe the main structure features of a rotating magnetic disk. Present an equation for the average time required to access the disk, and briefly explain the items involved in the average disk access time. (6 marks)