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Can someone tell me what is the actual meaning of cache access / memory access time ?

Is it the time to fetch a word/byte from cache or is it the time to search the cache or is it the sum of both?

If it's the time to fetch a byte then why do we add this time in hierarchical access ? It's not the searching time right?
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Its the sum of both

Yes, search time is implicit in access time. When we mention access time it includes search time unless specified  explicitly ...


In general access time in hardware, storage means the average time interval between a storage peripheral (usually a disk drive or semiconductor memory) receiving a request to read or write a certain location and returning the value read or completing the write.


Now the question is why we add this time in hierarchical access ?

That's because in case of hierarchical access when there is a miss in level 1 then only we move to level 2 . So there some time needed to reach in level 1 and some time needed to search if that required block is found in level 1 or not !

if not found we have to go to level 2 and search again .. so this (  reach to level 1 + first time search in level 1 ) time is need to add in case of hierarchical access .

If this is simultaneous access then this time is not needed because in case of simultaneous we can reach level 1 and level 2 at the same time .

Hope i am clear to you.
Sir, suppose there is a miss in L2 cache and a hit in main memory then can we access the word directly from main memory or should be transfer it to cache and then access?


If there is a miss in L2 cache and hit in Main memory then we bring back the word in cache as it requested by CPU and then access. 

We don't access that word directly from memory , it should be bring into cache because cache is close to cpu .memory access is take large time so for large data block each memory access takes long time ..hence we need that data block in cache so that time to access is less .

After access if it again need in near future then keep in cache , if not require then keep in memory .

0 votes
it is the time required to fetch a byte from cache . search time generally mention explicitly . if not mention we ignore search time.

we can say search time is implicit in access time , it is there but not mention.
edited by

Also read what Memory access time means , it is how long it takes for a character in memory to be transferred to or from the CPU , so it is same as fetching a byte from memory .

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