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For this question, they’ve solved it using the formula AMAT = H1T1 + M1(H2T2 + M2 ...) and so on.

However, since the question has directly given the hit time of the cache, I thought it’d be more appropriate to use the formula: 

AMAT = HitTime(cache) + MissRate(Cache)*(HitTime(MM) + MissRate(MM)*(HitTime(Secondary)))

So, which one is more appropriate and how would you differentiate between the two use cases? 

in CO & Architecture by (377 points) | 16 views

@shashin If you could help, that'd be great. 


if it is found in main memory access time is xxxx and access time of secondary storage is yyyy

This statement seems inconsistent and so I would interpret it either way. Either they should say "access time in case of cache miss is xxxx", or "access time of main memory is xxxx", or something along those lines. 

As long as you have the approach right, you shouldn't worry.

Fair enough, but what is the more obvious case where we have to use the former formula i.e H1T1? I mean, what particular phrasing gives it away that we'll use it?
Well, pretty much something that says "access time in case of cache miss....".

But the best answer to this would be to go through all the previous year questions on cache, and digest the language they've used. There shouldn't be any sort of ambiguity here - so better look at the source itself.

@goxul Cache memory problems on testbook are erroneous, so I suggest not to spend too much time on them.

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