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Consider the unpipelined machine with 12ns clock cycles. It uses 4 cycles for ALU operations and branches, whereas 5 cycles for memory operations. Assume that the relative frequencies of their operations are 30%, 20%, 20% repectively. Suppose that the due to clock skew and setup, pipelining the machine adds 1ns overhead to the clock. How much speed up in the instruction execution rate will we gain from a pipleline ?

a) 2.0 times  b) 3.1 times c) 2.8 times d) 3.5 times

1 Answer

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In NonPipeline System

CPI=0.3*4+0.2*4+0.2*5=3

Execution time per instruction=CPI*Clock Duration=3*12=36ns

In Pipeline System

CPI=1=12ns

overhead =1ns more

So execution time foreach instruction = 13ns

So SpeedUp=$\frac{Execution Time of Nonpipeline System}{Execution Time of Pipeline System}$

                    =36/13=2.8

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