Question

A two level memory is having 140 ns average access time without the level and 30 ns with level. If the fastest memory access time is 20 ns the what will be the hit ratio?

Answer 1

We can use the formula:
average data access time = Cache access time + (1 - hit ratio) main memory access time;
So if hit ratio will be x, we can write the next:
20 nS + (1 - x) 140 nS = 30 nS
20 nS + 140 nS - 140 nS x = 30 nS
- 140 nS x + 160 nS = 30 nS
- 140 nS x = - 130 nS
x = 0.928
So hit ratio will be 0.928 or 92.8%