ITPEC FE Morning October 2020 Question 10
ITPEC FE Morning October 2020 — Question 10 of 80
Cache Hit/Miss — Average Memory Access Time — calculate effective access time using hit/miss ratio.
Given:
- Miss ratio = 0.2 → Hit ratio = 0.8
- Cache access time = 75 ns
- Main memory access time = 1500 ns (includes cache check time)
Formula:effective_time = hit_ratio × cache_time + miss_ratio × main_memory_time
Calculation:= 0.8 × 75 + 0.2 × 1500= 60 + 300= **360 ns**
Why not others:
- (a) 315 — incorrect formula or wrong ratio application
- (c) 1,215 — swapped hit/miss ratios: 0.2 × 75 + 0.8 × 1500
- (d) 1,260 — incorrectly adds cache time on every access plus miss penalty
Key rule: When the problem states main memory access time includes cache check time, do NOT add cache time again on a miss — use main memory time directly.
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