Spring 1990-quiz1

# Spring 1990-quiz1 - Computer Science 252 Quiz#1 Name 1 The...

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1 Quiz #1 S90 Answers 9 / 2 4 / 9 Computer Science 252 Quiz #1 Name:_________________ 1. The cost/performance of two microprocessors is to be examined, each running the same instruction set. The first option is a Galium Arsenide (GaAs) microprocessor. A GaAs wafer that is 10 cm ( 4 inches) in diameter costs \$1000. The manufacturing process creates 4 defects per square centimeter. The microprocessor fabricated in this technology is expect to have a clock cycle rate of 250 MHz, with an average clock cycles per instruction of 1.5 if we assume an infinitely fast memory system. The size of the GaAs microprocessor is 1.0 cm by 1.0 cm. (Assume α is 2.0 for GaAs.) The second option is a CMOS microprocessor. A 15 cm ( 6 inch) wafer with 2 defects per square centimeter costs \$500. The 1.0 cm by 2.0 cm microprocessor executes multiple instructions per clock cycle to achieve an average clock cycles per instruction of 0.75, assuming an infinitely fast memory while achieving a clock rate of 50 MHz. (The microprocessor is larger because of on chip caches and executing multiple instructions per clock cycle.) You found that a memory system can be built for either microprocessor, and that the average extra time for memory accesses per instruction (for instructions and data) is the same for each microprocessor: 10 ns. a) What is the cost of an untested GaAs die for this microprocessor? (Use information from the book to supplement the information here if anything is missing.) Show your work. [4 points] Dies per wafer = π * (Wafer diameter/2) 2 Die area π * Wafer diameter f8e5f8e5f8e5f8e5f8e5f8e5f8e5f8e5f8e5f8e5f8e5 2 * Die area – Test dies per wafer Dies per wafer = π * (10/2) 2 1 π * 10 f8e5f8e5f8e5f8e5f8e5 2 * 1 – 5 = π * (25– 10 f8e5 2 ) – 5 = 56 – 5 = 51 Die yield = Wafer yield * { } 1 + Defects per unit area * Die area α α = 90% * { } 1 + 4 * 1 2 2 = 10% Cost of die = Cost of wafer Dies per wafer * Die yield = \$1000 51 * 10% = \$196.08 Forget test die -1 (unless said assume no test die) b) What is the cost of an untested die for the CMOS microprocessor? (Use information from the book to supplement the information here if anything is missing.) Show your work. [4 points] Dies per wafer = π * (15/2) 2 2 π * 15 f8e5f8e5f8e5f8e5f8e5 2 * 2 – 5 = π * (25– 10 2 ) – 5 = 64 – 5 = 59 Die yield = Wafer yield * { } 1 + Defects per unit area * Die area α α = 90% * { } 1 + 2 * 2 2 2 = 10% Cost of die = Cost of wafer Dies per wafer * Die yield = \$500 59 * 10% = \$84.75

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2 Quiz #1 S90 Answers 9 / 2 4 / 9 c) What is the native MIPS rating of each microprocessor? Which is faster and by what percent? Show your work. [6 points] CPI GaAs = 1.5 + 10/4 = 4.0 MIPS GaAs =
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