GATE CSE 2022 | Question: 23

Question

A cache memory that has a hit rate of $0.8$ has an access latency $10 \; \text{ns}$ and miss penalty $100 \; \text{ns}.$ An optimization is done on the cache to reduce the miss rate. However, the optimization results in an increase of cache access latency to $15 \; \text{ns},$ whereas the miss penalty is not affected. The minimum hit rate (rounded off to two decimal places) needed after the optimization such that it should not increase the average memory access time is _______________.

Comments

Answer is 0.85. 

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note: this is done in serial connection but not parallel connection ie parallel doesnot even exist according to standard textbooks refer to go classes lectures by deepak sir for better understanding

 

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AMAT = (Hit Time) + (1 - H) (Miss Penalty) 

Answer 1

original

Tavg=10ns+(1-0.2)*100ns  , Tavg=30ns

after optimization

Tavg=15ns+X*100ns

30ns=15ns+X*100ns

30ns-15ns=X*100ns

15ns/100ns=X

X=0.15  (miss rate)

therefore, Hit rate=1-miss rate = 1-0.15 = 0.85

ans=0.85