Cache Memory

Question

Consider the following statements:
S₁ : Doubling the line size halves the number of tags in the cache.
S₂ : Doubling the associativity doubles the number of tags in the cache.
S₃ : Doubling the line size usually reduce compulsory misses.
Which of the above statements is always true?

Comments

@Arjun Sir plz confirm point S2 and S3.

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this question has different answers for the number of tags vs. the number of tag bits.

Many institutes just create unnecessary confusion. They write one thing and answer for the other context.

Answer 1

1) Doubling the line size decreases no of lines by half  so , since tags are attached with each line then no of tags will also get

    halved.

2) it is not true since associativity just group no of lines together so data can be randomly stored in a line unlike direct mapping , no of      lines remain same  , tags remain same.

3) its true since compulsory miss occurs when we dont find requested data in cache lines for first time after that if its requested it

    will be either conflict or capacity miss, so increasing block size means increase in capacity of line of cache and due to property

    of locality of refrence which cache utilizes wil fetch the data along with data around and chances are the we might find next to          be requested data in this extra fetched data, usually

Comments

no , compulsory misses occurs due to first time access of a block

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@srestha

@Lone Wolf

pls check S1

doubling the line size halves the no. of tags  ===> no. of tags gets halved or no. of comparators gets halved??

 

 

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Answer is s1 and s3 ... Yes number of lines are reduced by half and tags attached to it are reduced by half ... comparators depends on associativity of cache and even tag bits are also depends on associativity as well...

" no , compulsory misses occurs due to first time access of a block " -- It is correct .. It happens if we increase block size since it improves spatial locality which decreases first time visits of extra words that are included bcz of increased size...

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Concept: to reduce compulsory misses  prefetching should be done.

So, if we increase the line size that means we are prefetching extra words .

Hence, we can say that it reduces compulsory misses.

Answer 2

Doubling the line size wont reduce the compulsory misses.

Compulsory miss occur due to first acces of the block.

Total no. of diffrnt block requests = no. compulsory miss

Comments

Doubling line size reduces compulsory misses