ITPEC FE Morning April 2019 Question 11
ITPEC FE Morning April 2019 — Question 11 of 80
Cache Hit Rate and Average Access Time — identify what increases average memory access time.
Formula: effective_time = hit_ratio × cache_time + (1 - hit_ratio) × main_time
- •A decrease in hit rate means more accesses go to slow main memory → average time increases
- •A decrease in cache access time → average time decreases
- •A decrease in miss penalty → average time decreases
- •A decrease in miss rate = increase in hit rate → average time decreases
Why not others:
- (a) Faster cache access → lower average time
- (c) Lower miss penalty → lower average time
- (d) Lower miss rate = higher hit rate → lower average time
Key rule: Only changes that shift more accesses toward slower memory (or make that slower memory even slower) will increase average access time.
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