Question

A five-stage pipeline has stage delays of 150, 120, 150, 160 and 140 nanoseconds. The registers that are used between the pipeline stages have a delay of 5 nanoseconds each.

The total time to execute 100 independent instructions on this pipeline, assuming there are no pipeline stalls, is ______ nanoseconds.

Answer 1

To calculate the total time to execute 100 independent instructions on a five-stage pipeline, determine the longest stage delay, add the register delays,

Step-by-step explanation:

The correct answer is option 29500 nanoseconds. To calculate this, first, find the longest stage delay in the pipeline, which will be the bottleneck. The longest delay here is 160 nanoseconds. There are four additional registers with a 5 nanosecond delay each, so we add 20 nanoseconds (4 registers * 5 nanoseconds per register) to the longest stage to get the total time for each cycle: 180 nanoseconds.

Since we execute the first instruction completely before bringing in new instructions in a non-overlapping sequence, it would take 5 cycles for that first instruction. This adds up to 900 nanoseconds (5 stages * 180 nanoseconds). However, because this is a pipeline, each subsequent instruction starts executing every 180 nanoseconds after the first. So, for 100 instructions, the execution time is the time taken by the first instruction plus 99 instructions multiplied by the cycle time.

Therefore, the total time for 100 instructions is 900 nanoseconds (initial instruction) plus 17820 nanoseconds (99 instructions * 180 nanoseconds per instruction), resulting in 29500 nanoseconds.