GATE | GATE-CS-2014-(Set-2) | Question 65

In designing a computer’s cache system, the cache block (or cache line) size is an important parameter. Which one of the following statements is correct in this context?
(A) A smaller block size implies better spatial locality
(B) A smaller block size implies a smaller cache tag and hence lower cache tag overhead
(C) A smaller block size implies a larger cache tag and hence lower cache hit time
(D) A smaller block size incurs a lower cache miss penalty


Answer: (D)

Explanation: Block : The memory is divided into equal size segments. Each segment is called a block. Data in cache is retrieved in form of blocks. The idea is to use Spatial Locality (Once a location is retrieved, it is highly probable that the nearby locations would be retrieved in near future).

TAG bits : Each cache block is given a set of TAG bits to identify which main memory block is present in that cache block.

Option A : If the block size is small, there would be less number of near-by address for future references by CPU to be present into that block. Hence this is not better spatial locality.

Option B : If the block size is smaller, no of blocks would be more in cache, hence more cache tag bits would be needed, not less.

Option C : Cache tag bits are more ( because more no of blocks due to smaller block size ), but more cache tag bits can’t lower the hit time ( even it will increase ).

Option D : If there is a miss at cache memory ( i.e. the needed block by the CPU is not present in the cache memory ), then that block has to be moved from next lower level of memory ( lets say main memory ) in the memory hierarchy, and if the block size is lower, then it takes less time to be placed into cache memory, hence less miss penalty.

Hence option D.


Quiz of this Question

My Personal Notes arrow_drop_up