ISRO 2008-ECE Cache Memory

Question

The advantage of write (copy) back data cache organization over write through organization is

(a) Main memory consistency

(b) Write allocate on write miss

(c) Less memory bandwidth

(d) Higher capacity requirement

Comments

Answer should be B) bcoz for write data is update in cache and when miss occurs write allocate is used then cache update. A) cannot be answer bcoz we update cache and it is possible it can have inconsitent main memory.

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@rahul jain, option A is not the answer as in write bakc plicy,main memory is not updated everytime a write occurs,only when a block is replaced in cache,that block is written to main memory.so,consistency is not always maintained.

and whats the prob with option C??

as we do not need to write to main memory everytime,is'nt less bandwith will be ok??

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Actually I am not able to interpret option C) and B) seems correct, not sure though

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can u elaborate option B a little more if possible?actually i am nt that aware of write allocate policy.
thanks

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https://web.cs.iastate.edu/~prabhu/Tutorial/CACHE/interac.html

Good read☺

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@Akriti you are correct C is the answer. Also it is given in the link I gave and I also verified this question by answer key on a website. Write allocate will actually increase write operation time.

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thanks for the link @rahul :)

Answer 1

Answer would be c option as in write back technique when the block to be replaced is dirty block either due to case of read allocate or write allocate then it is written to main memory however in case of write through technique every time whether it is dirty block or nt when ever it is replaced it is written to main memory simultaneously so lesser memory bandwidth in first case here