GATE Computer Science (CS) 2020 Solved Papers

Question : 21 of 65

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A direct mapped cache memory of 1 MB has a block size of 256 bytes. The cache has an access time of 3 ns and a hit rate of 94%. During a cache miss, it takes 20 ns to bring the first word of a block from the main memory, while each subsequent word takes 5 ns. The word size is 64 bits. The average memory access time in ns (round off to 1 decimal place) is _______.

Your Answer:

Validate

Solution:

Cache Memory

=1 {MB}

Word size

=64

bit

=8 {B}

Block size

=256 {B}

Hit rate,

x=0.94

miss rate

=1-x=0.06

Cache access time,

{Tc}=3 {ns}

Number of words {/} Block

=256 {\/ }8=32

Using Hierarchical Approach,

Tavg=( {x} . {Tc})+(1- {x})[ {T} {c}+ {st}

word access time

+

remaining word access time

]

Tavg=(0.94 × 3)+(1-0.94)[3+20+(31 × 5)]

Tavg

=13.5 {ns}

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