Question

What is the hit ratio of a cache memory.If cache memory access time is 30ns,main memory access time is 150ns and avg access time is 42ns.

Answer 1

Simultaneous Access for cache and main memory

42= H(30) + (1-H) (150)

So H = 0.9

If hierarchical Access

42 =H(30) + (1-H)(150+30)

H = 0.92

But in question nothing mentioned so simultaneous Access should be the ans...

Comments

default is not simultaneous access.

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Sir can u give some light on this topic ??
About simultaneous or hierarchical ...or any reference ...

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@Arjun if nothing is mentioned in the question then what we should take simultaneous or herarichal access???

Answer 2

Avg memory access time= hitratio(cache access time)+missratio(cache access time+memory access time)

 Because even in case of miss, we first look into cache and then access memory.

here,

42= x(30)+(1-x)(180)

on solving, x=0.92..