Pipeline

Question

Suppose that a computer prefetches upto $20$ instructions in advance. on the average four of these are conditional branches, each with a probability of $90 \%$ of being predict correctly. what is the probability that the prefetching is on the right track?

Comments

it should be $0.9 ^{4}=0.6561$

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Can you explain Why Only 0.9 isn't correct.

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$0.9$ is the probability of each conditional instruction being predicted correctly.

Prefetching will be on the right track if all the $4$ instructions are being predicted correctly.

so $0.9 \times 0.9 \times 0.9 \times 0.9$ is correct

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thanks