GATE CS 2025 Set 1 — Question 53
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Computer Organization & Architecture → Memory Hierarchy & Cache → Cache Numericals
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Question
A computer has a memory hierarchy consisting of two-level cache (L1 and L2) and a main memory. If the processor needs to access data from memory, it first looks into L1 cache. If the data is not found in L1 cache, it goes to L2 cache. If it fails to get the data from L2 cache, it goes to main memory, where the data is definitely available. Hit rates and access times of various memory units are shown in the figure. The average memory access time in nanoseconds () is ________. (rounded off to two decimal places)
Correct answer
11.83 to 11.87
Solution
The average memory access time () in a multi-level cache hierarchy can be calculated as follows:Given:
- L1 cache: Hit rate () = , Access time () = ns
- L2 cache: Hit rate () = , Access time including L1 miss penalty () = ns
- Main Memory: Access time including L1 and L2 miss penalties () = ns
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