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Suppose you design a computer with a ten-stage Pipeline to execute one instruction, with each stage taking 5nsec

A)how long will it take to execute a program that has 30 sequential instructions. Answer: 195nsec

B) how long will it take to execute a program that has 30 sequential instructions in a non-pipeline computer Answer: 1500nsec

can some one please help me to understand how was the answer achieved.

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    $\begingroup$ I suggest that you read up on how pipelines work. These are very simple calculations once you understand that. $\endgroup$
    – David Richerby
    Commented May 31, 2017 at 9:52

2 Answers 2

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Suppose the first instruction enters the pipeline at time $0$. Each successive instruction enters $5$ ns after the previous one. The first instruction exits the pipeline at time $10\cdot 5$ ns and each of the other $29$ instructions exits $5$ ns after the previous one. In sum, $10 \cdot 5 + 29 \cdot 5 = 195$ ns.

For the non-pipelined processor, the somewhat pessimistic assumption is made that each instruction takes $10\cdot 5$ ns to execute; then, $30 \cdot 50 = 1500$.

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An instruction needs 10 times 5 nsec to execute. With pipelining, the next instruction can start when the previous one is in the next pipeline stage, that is 5 nsecs after the previous one started. Without pipelining, the next instruction starts only when the previous one has finished, that is after 10 times 5 sec. The rest is basic arithmetic.

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