Consider a system with 2 level caches. Access times of Level 1 cache, Level 2…
20042016
Consider a system with 2 level caches. Access times of Level 1 cache, Level 2 cache and main memory are 1 ns, 10ns, and 500 ns, respectively. The hit rates of Level 1 and Level 2 caches are 0.8 and 0.9, respectively. What is the average access time of the system ignoring the search time within the cache?
Answer: C. 12.6 ns — Average Memory Access Time (AMAT) AMAT = h1 × t1 + (1 − h1) × h2 × (t2 + x1) + (1 − h1) × (1 − h2) × (tm + x1 + x2) Here, x1 and x2 are the search times for…
- A.
13.0 ns
- B.
12.8 ns
- C.
12.6 ns
- D.
12.4 ns
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Correct answer: C
Average Memory Access Time (AMAT)
AMAT = h1 × t1 + (1 − h1) × h2 × (t2 + x1) + (1 − h1) × (1 − h2) × (tm + x1 + x2)
Here, x1 and x2 are the search times for L1 and L2 caches respectively. As per the question, these search times can be considered as 0.
Substituting the given values:
AMAT = 0.8 × 1 + 0.2 × 0.9 × 10 + 0.2 × 0.1 × 500
AMAT = 12.6 ns
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