Question

Consider a non-pipelined processor with a clock rate of 2.5 gigahertz and average cycles per instruction of four. The same processor is upgraded to a pipelined processor with five stages; but due to the internal pipelined delay, the clock speed is reduced to 2 gigahertz. Assume that there are no stalls in the pipeline. The speed up achieved in this pipelined processor is _____.

Answer 1

Speedup = ExecutionTimeOld / ExecutionTimeNew

ExecutionTimeOld = CPIOld * CycleTimeOld

[Here CPI is Cycles Per Instruction]

= CPIOld * CycleTimeOld

= 4 * 1/2.5 Nanoseconds

= 1.6 ns

Since there are no stalls, CPUnew can be assumed 1 on average.

ExecutionTimeNew = CPInew * CycleTimenew

= 1 * 1/2

= 0.5

Speedup = 1.6 / 0.5 = 3.2