Correct Answer - Option 2 : 98%
Concept:
The average memory access time is given by:
Average memory access time = Hit ratio × access time in cache memory + (1 – Hit ratio) × Access time in main memory
Calculation:
Given:
Hit ratio = ? (Let it be h)
Main memory access time = 1200 ns
Cache memory access time = 100 ns
Average memory access time = 120 ns
So, 120 = h × 100 + (1 – h) 1200
120 = 100 h + 1200 – 1200 h
1100 h = 1080
\(h = \frac{{1080}}{{1100}} = 0.9818\)
∴ Hit ratio = 98%