1. Modern CPU chips have one, two, or even three levels of cache on chip. Why are multiple levels of cache needed?
2. Suppose that a CPU has a level 1 cache and a level 2 cache, with access times of 1 nsec and 2 nsec, respectively. The main memory access time is 10 nsec. If 20% of the ac- cesses are level 1 cache hits and 60% are level 2 cache hits, what is the average access time?