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Computer Org. Lecture 19 Name:_______________ 1. Suppose you are shopping for a new laptop computer, what criteria would you use to compare different models? 2. Chapter 6 deals with performance. In the past, computer performance increases have been due to Moore’s law (Gordon Moore - cofounder of Intel) - observation/prediction that the number of transistors that could be put on a single chip would double every year (later changed to 18 months). a) What kind of curve (# transistors vs. time) does Moore’s law predict? (linear, quadratic, exponential, etc.) b) Why might Moore’s law not be valid in the future? c) As gate density increases on a chip, why would clock speed increase? Computer Performance Terminology: a) Efficiency = total time executing useful work optimal time = actual time total time b) Throughput - amount of work performed per unit time c) Latency - wait time between the activation of an operation and its actual start (alternatively: time from activation of an operation until the completion) performance of A execution time on B d) Relative Performance of Computer A to B = performance of B = execution time on A execution time on reference machine Speedup ratio = execution time on improvement machine Lecture 19 Page 1 Computer Org. Lecture 19 Name:_______________ e) Benchmark - suite of programs and data run on computers to compare execution times f) Rate - rate at which tasks are executed. (e.g., Quake frames per second) 2. Comment on the quality of each metrics used to measure computer performance: a) clock rate b) MIPS (millions of instructions per second) c) MFLOPS (millions of floating point operations per second) d) CPI - (Clock cycles per instruction) 3. On way to speedup a program is to parallelize part of it (e.g., use multiple core on the same program). You can estimate the expected speedup using Amdahl’s law. Let’s develop Amdahl’s law using the above picture: ts is the single processor time fs is the fraction runs on single processor fp is the fraction runs on p processors Tp is the execution time on parallel system with p processors Tp = Speedup, S = Lecture 19 Page 2 Computer Org. Lecture 19 Name:_______________ 4. From the above graph, what architectural improvements seem to have the biggest impact on performance? Lecture 19 Page 3