GATE CS 2017 Set 2 — Question 45

NAT+2 / -0HardCache NumericalsMemory Hierarchy & CacheComputer Organization & Architecture

Computer Organization & Architecture → Memory Hierarchy & Cache → Cache Numericals

Last updated 5 September 2026

Question

The read access times and the hit ratios for different caches in a memory hierarchy are as given below. Cache Read access time (in nanoseconds) Hit ratio I-cache 2 0.8 D-cache 2 0.9 L2-cache 8 0.9 The read access time of main memory is 90 nanoseconds. Assume that the caches use the referred-word-first read policy and the write back policy. Assume that all the caches are direct mapped caches. Assume that the dirty bit is always 0 for all the blocks in the caches. In execution of a program, 60% of memory reads are for instruction fetch and 40% are for memory operand fetch. The average read access time in nanoseconds (up to 2 decimal places) is________.

Cache	Read access time (in nanoseconds)	Hit ratio
I-cache	2	0.8
D-cache	2	0.9
L2-cache	8	0.9

ARAT = 0.6 \times ARAT_{instr} + 0.4 \times ARAT_{data}

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ARAT = 0.6 \times ARAT_{instr} + 0.4 \times ARAT_{data}

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