Answer to Question #313977 in Computer Networks for Anna

Question

A 4-stage pipeline has the stage delays as 150, 120, 160 and 140

nanoseconds respectively. Registers that are used between the stages have a

delay of 5 nanoseconds each.

Question: Assuming constant clock rate, calculate the total time taken to

process 1000 data items on this pipeline.

Answer 1

Pipelining requires all stages to be synchronized meaning, we have to make the delay of all stages equal to the maximum pipeline stage delay which here is 160.

Time for execution of the first instruction $= (160+5)\times3 + 160$

= 655 ns (5 ns for intermediate registers which is not needed for the final stage).

Now, in every 165 ns, an instruction can be completed. So, Total time for 1000 instructions $= 655 + 999\times165$

$= 165.49 microseconds$

$=165.5 microsends$