[Architecture Simulator]

Which statement most accurately describes sectored cache and small cache block size?

Question

[Architecture Simulator]

Which statement most accurately describes sectored cache and small cache block size?

BlackTom AI · Accepted Answer

Sectored caches group multiple small data sub-blocks under a single tag, and using smaller cache block sizes reduces the amount of data fetched on each miss—together these effects can lower memory bandwidth use.

1) Relevant knowledge points and concepts
- Memory bandwidth is consumed when the processor misses in cache and the cache fetches data from main memory; the number of bytes transferred per miss matters.
- Cache block (line) size determines how many bytes are transferred per miss; larger blocks exploit spatial locality but can waste bandwidth if locality is low.
- A sectored cache keeps one tag for a larger sector but stores data as smaller sub-blocks. This reduces tag storage overhead associated with small blocks and enables sub-block fetches or more effective use of capacity.

2) Step-by-step reasoning
- If block size is reduced, each miss fetches fewer bytes, so for the same miss count memory bytes transferred drop proportionally.
- Without sectoring, making blocks smaller increases tag overhead (more tags per capacity), which may force reduced data capacity or higher miss rate; that can negate bandwidth savings.
- Sectored caches remove that penalty by sharing one tag across multiple small sub-blocks (a sector), so you can keep small block granularity without prohibitive tag cost. That yields both lower bytes-per-miss and preserved or improved hit rate.

3) Calculation example (intermediate steps)
- Compare 64 B vs 16 B block size for 100 misses:
  - 64 B: 100 × 64 B = 6,400 B transferred
  - 16 B: 100 × 16 B = 1,600 B transferred → 4× less bandwidth
- Tag overhead example (8 B tag):
  - 16 B blocks without sectoring: tag/data = 8/16 = 50%
  - 16 B blocks with sectors of 64 B (one 8 B tag per four 16 B blocks): tag/data = 8/64 = 12.5% (same as 64 B lines)

4) Why the correct answer is correct
- Small block size directly reduces bytes transferred per miss. Sectored caches make small blocks practical by lowering tag overhead and by allowing selective fetching of sub-blocks, so together they can reduce total memory bandwidth demand.

5) Why other options are incorrect
- No alternative options were provided in the prompt; common incorrect claims would be that sectoring or small blocks always increase bandwidth—this is false because the combination above reduces wasted prefetch and tag overhead, lowering bandwidth in many workloads.

6) Conclusion
- Therefore, the statement "Sectored cache and small cache block size could reduce the memory bandwidth requirements." is correct and matches the provided answer.

[Architecture Simulator] Which statement most accurately describes sectored cache and small cache block size?单项选择题

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