UPPCL 2018AE

Question

Suppose when there is cache “Miss” then memory Access is 30ns

and when cache “Hit” then memory access time is 3ns

if 80% is cache hit then effective memory access

• A. 9ns
• B. 8.4ns
• C. 3ns
• D. 9.10ns

Comments

Actualy the answer to the given question is 9ns only... but the ques in exam was different .. for that the ans is 8.4ns

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Answer is 8.4 ns.

Because here overall memory access time is 30 ns. Read the question carefully "cache Miss then memory Access is 30ns ".

That means here talking about all included time i.e miss + hit.

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If my memory can recall it correctly , I am certain the question was same as given above ,  in case of cache miss , memory access time was 30ns.

Answer 1

Here the answer is B)8.4

Suppose when there is cache “Miss” then memory Access is 30nsa and when cache “Hit” then memory access time is 3ns if 80% is cache hit then effective memory access

Ans: 8.4ns
0.8*3+0.2*30

A cache memory needs an access time of 3 ns and main memory 30 ns, what is average access time of CPU (assume hit ratio = 80%)?
Ans: 9ns
0.8*3+0.2*33