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?

  1. A.

    13.0 ns

  2. B.

    12.8 ns

  3. C.

    12.6 ns

  4. 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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