Please Help!!! The CPU design team is choosing between two implementations of th

Question

Please Help!!!

The CPU design team is choosing between two implementations of the same instruction

set each with three classes of instructions. Parameters for the two possibilities are given in the

following table.

a) For a program with 20% ALU instructions, 10% control instructions and 70% memory

instructions, which design will be faster? Give a quantitative CPI average for each case. Show all work

b) For a program with 70% ALU instructions, 10% control instructions and 20% memory

instructions, which design will be faster? Give a quantitative CPI average for each case. Show all work.

CPU-1 CPU-2 Clock Rate 500MHz 350MHz CPI for ALU Instruction 1 1 CPI for Control Instruction 2 1 CPI for Memory Instruction 2.5 1

Explanation / Answer

a)

Average CPI for Pipelined Version = (0.2*1 + 0.1*2 + 0.75*2.5) = 2.27

Average CPI for Non-Pipelined Version = (0.2*1 + 0.1*1 + 0.7*1) = 1.0
CPU execution time for Pipelined version = 2.5/(500 Mhz) = 4.5ns
CPU execution time for Non-Pipelined version = 1.0/(350 Mhz) = 2.8ns
The non-pipelined version is faster.

b)

Average CPI for Pipelined Version = (0.7*1 + 0.1*2 + 0.2*2.5) = 1.4

Average CPI for Non-Pipelined Version = (0.7*1 + 0.1*1 + 0.2*1) = 1.0
CPU execution time for Pipelined version = 2.5/(500 Mhz) = 4.5ns
CPU execution time for Non-Pipelined version = 1.0/(350 Mhz) = 2.8ns
The non-pipelined version is faster.

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