In designing a computer’s cache system, the cache block (or cache line) size…

Answer: A smaller block size incurs a lower cache miss penalty.

Why this is true:

• Miss penalty is largely the time to transfer a cache block from lower-level memory to the cache. A smaller block contains fewer bytes, so the transfer takes less time and the miss penalty is lower.

• Thus, reducing block size reduces miss penalty but does not by itself guarantee better overall performance.

Important trade-offs to keep in mind:

• Spatial locality: Larger blocks exploit spatial locality better by bringing adjacent data with one miss; smaller blocks reduce this benefit and can increase miss rate.

• Tag overhead: For a fixed cache capacity, smaller blocks mean more blocks and therefore more tag entries, increasing total tag storage overhead.

• Hit time: Cache hit time is influenced by tag comparison logic, associativity, and data-path complexity; block size does not directly reduce hit time in the way suggested by the incorrect statement linking larger tags to lower hit time.

Why the other given statements are incorrect:

• The statement 'A smaller block size implies better spatial locality' is incorrect because smaller blocks bring in less contiguous data, reducing the ability to use spatial locality.

• The statement 'A smaller block size implies a smaller cache tag and hence lower cache tag overhead' is incorrect because smaller blocks increase the number of blocks (and thus the number of tag entries) for a fixed cache capacity.

• The statement 'A smaller block size implies a larger cache tag and hence lower cache hit time' is misleading: while smaller blocks increase total tag storage, that does not cause lower hit time. Hit time depends on implementation details such as tag comparison circuitry and associativity.

Summary: Smaller blocks reduce miss penalty but can increase miss rate and tag overhead; selecting block size requires balancing these competing effects based on workload locality and system constraints.