1. Compare the architectures in terms of total time in nanoseconds. Computer A h
ID: 662424 • Letter: 1
Question
1. Compare the architectures in terms of total time in nanoseconds.
Computer A has a clock speed of 2HGz, a CPI of 2.0, and runs 100 instructions.
Computer B has a clock speed of 1GHz, a CPI of 1.5, and runs 50 instructions.
a. Which is faster? Show your work.
b. If you had to improve one of these, which would you target? How and why (from a high level)?
2. Let's say we have Computer C, where the clock speed is 10GHz, and runs 500 instructions. Of the 500 instructions, 100 have a CPI of 3 and 400 have a CPI of 1.
a. How long does this take?
b. If this is the same program as problem #1, would you choose to use this one?
c. What disadvantage does computer C have compared to A and B?
3. Continuing with Computer C. Let's say when the CPI is 3, we slow the clock speed to 5GHz. Now how long does it take to complete?
4. Let's say we can improve the performance of the multiply function by 5x. The multiply is used 15% of the time.
a. How much faster is the newly designed system?
b. When we improve the multiply unit, the adder, used 30% of the time, is slowed by 50% (time is doubled). What is the new speedup?
c. What is I switch the numbers? The adder is now faster by 5x and the multiplier is slow by 50%, what is the new speedup?
Explanation / Answer
# multiple questions in one question, so answering to question which i know the answer
CPU time = (Instruction count x CPI) / clock rate
For Computer A,
Given clock rate 2HGz, a CPI of 2.0, and runs 100 instructions
Cpu time for A = 100 * 2 /(2* 10^9) = 100ns
Given for computer B, clock rate 1GHz, a CPI of 1.5, and runs 50 instructions
Cpu time for B = 50 * 1.5 /(10^9) = 75ns
So B is faster
If I had to improve one of these, I would you target A computer beacause it runs more instructions
2)
a) CPU time for Computer C = (100 * 3 +400 * 1) / 10 *10 ^9 = 70 ns
b) I would choose Computer C because it is mix diffrent CPI for instructions
3)
CPI =3, Clock rate = 5GHz
CPU time = 3*500/(5*10^9) = 300 ns
4) invalid question more info needed
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