ITPEC FE Morning April 2022 Question 13
ITPEC FE Morning April 2022 — Question 13 of 80
Cache Effective Access Time — rank systems by weighted memory access time.
Formula: effective = hit_ratio × cache_time + (1 - hit_ratio) × main_time
If no cache, effective time = main memory access time.
Calculations:
- A (no cache): 15 ns
- B (no cache): 30 ns
- C (hit=60%): 0.6 × 20 + 0.4 × 70 = 12 + 28 = 40 ns
- D (hit=90%): 0.9 × 10 + 0.1 × 80 = 9 + 8 = 17 ns
Sorted (shortest first): A (15) → D (17) → B (30) → C (40)
Why not others:
- (a) A, B, C, D — alphabetical order, ignores calculations
- (c) C, D, A, B — reversed (slowest first)
- (d) D, C, A, B — incorrect ordering
Key rule: Cache doesn't always help — a low hit rate with slow main memory (system C) can be worse than no cache with fast main memory (system B).
AI-generated — may contain errors
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