GATE 2014 CS (CS3) – Question 54

Computer Organization and Architecture · Memory Interfacing and Hierarchy · 2 marks · Numerical answer

Memory access takes 1 ns for a cache-hit read, 5 ns for a cache-miss read, 2 ns for a cache-hit write and 10 ns for a cache-miss write. An instruction sequence performs 100 instruction fetches, 60 memory-operand reads and 40 memory-operand writes. Cache hit ratio is 0.9. Find average access time (ns).

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Correct answer: 1.68 to 1.68

Explanation

There are160readsincluding instruction fetches and40writes. Mean read time0.9×1+0.1×5=1.4ns; mean write time0.9×2+0.1×10=2.8ns. Overall(160×1.4+40×2.8)/200=**1.68ns**. Reads and writes do not have equal weights.