A certain microprocessor requires either 2, 3, 4, 8, or 12 machine cycles to per

Question

A certain microprocessor requires either 2, 3, 4, 8, or 12 machine cycles to perform various operations. Twenty-five percent of its instructions require 2 machine cycles, 20% require 3 machine cycles, 17.5% require 4 machine cycles, 12.5% require 8 machine cycles, and 25% require 12 machine cycles.


a) What is the average number of machine cycles per instruction for this microprocessor?

b) What is the clock rate ( machine cycles per second) required for this microprocessor to be a "1 MIPS" processor?

c) Suppose this system requires an extra 20 machine cycles to retrieve an operand from memory. It has to go to memory 40% of the time. What is the average number of machine cycles per instruction for this microprocessor including its memory fetch instructions?

Explanation / Answer

5.8 cycles/instruction. It's probability of it * number of cycles so 2*.25+3*.2+4*.175+8*.125+12*.25=5.8 5.8 MHz so we can get the 5.8 cycles per instruction * 1 million instructions per second gets us 5.8 million cycles per second (2*.25+3*.2+4*.175+8*.125+12*.25)+20*.4=13.8. I was checking my answers with a key and I see it is 13.25. If the second is right, I'll relook at it in a bit.

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