Problem Set 2

Please submit for grading your answers to **2 and 6** in class on Friday,
Oct. 19.

- Discuss why processors based on load-store architectures facilitate access of information from memory in various sizes, but limit the operands in ALU operations to the word size. Also discuss why many high performance architectures require aligned memory access.
- You are considering an enhancement to the implementation of the divide operation in the processor your company is designing for a particular application. Assume that divide instruction takes 30 cycles before enhancement. It has been estimated that divide instructions account for 4% of all instructions, and that the average execution time of all other instructions is 2 clock cycles.
- Calculate the percentage of the total time spent for executing divide instructions.
- You have determined that it is possible to reduce the number of cycles required for division to 8, but that this would require a 12% increase in the clock cycle time. Nothing else will be affected. Would you proceed with this enhancement? Why?
- Calculate the maximum percentage decrease in the clock frequency that would still make the above enhancement (reducing divide time to 8 clock cycles) attractive.
- Suppose you are considering another modification which would cut down the number of clock cycles needed for division to 10 clock cycles, while not imposing any penalty on the clock cycle. Calculate the speedup in this case.

- Assume that we make an enhancement to a computer that improves some mode of execution by a factor of 15. Enhanced mode is used 40% of the time, measured as a percentage of the execution time when the enhanced mode is in use. Recall that Amdahl's law depends on the fraction of the original, unenhanced, execution time that could make use of the enhanced mode.
- What is the speedup we have obtained from fast mode?
- What percentage of the original execution time has been converted to fast mode?

- Textbook problem 2.6
- Textbook problem 2.11
- Textbook problem 2.12

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$Date: 2007-10-12 22:18:35 -0230 (Fri, 12 Oct 2007) $
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