A cache memory needs an access time of 30 ns and main memory 150 ns, what is…
2017
A cache memory needs an access time of 30 ns and main memory 150 ns, what is the average access time of CPU (assume hit ratio = 80%)?
- A.
60
- B.
30
- C.
150
- D.
70
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Correct answer: A
To calculate average access time, use the hierarchical memory model formula: T_avg = H * T_c + (1-H) * (T_c + T_m). Given Hit Ratio (H) = 0.8, Cache Time (T_c) = 30 ns, and Main Memory Time (T_m) = 150 ns. Substituting values: T_avg = 0.8 * 30 + (1 - 0.8) * (30 + 150). T_avg = 24 + 0.2 * 180. T_avg = 24 + 36. T_avg = 60 ns.
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