PDP Chapter 3: Quantitative Principles of Computer Design
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Questions and Answers

What does Amdahl's Law primarily help to determine in computer systems?

  • The cost-effectiveness of a hardware upgrade
  • The total number of operating units in a system
  • The energy consumption of a system
  • The overall performance gain from improvements (correct)
  • In the context of Amdahl's Law, what limits the performance improvement of a computer system?

  • The amount of memory available in the system
  • The speed of the input-output operations
  • The total operational costs of the enhancements
  • The fraction of time the enhanced mode can be used (correct)
  • When calculating execution times, which of the following represents the execution time before any enhancements?

  • Execution time non-enhanced (correct)
  • Execution time before enhanced
  • Execution time enhanced
  • Execution time new-enhanced
  • Which formula correctly represents the definition of execution time after an enhancement according to Amdahl's Law?

    <p>Execution time new = Execution time old-enhanced + Execution time enhanced</p> Signup and view all the answers

    What is the key factor that remains constant when comparing execution times before and after enhancements?

    <p>Execution time non-enhanced</p> Signup and view all the answers

    What is Amdahl’s Law primarily used for in computer science?

    <p>To calculate the overall performance speedup for a system based on its components.</p> Signup and view all the answers

    Using Amdahl's Law, if a processor spends 40% of its time on computation, what fraction remains for other operations?

    <p>0.6</p> Signup and view all the answers

    In the web serving application example, what does a speedup factor of 10 signify?

    <p>The new processor executes computations 10 times faster than the original.</p> Signup and view all the answers

    If a system demonstrates a theoretical maximum speedup of approximately 1.67, what does this imply?

    <p>Performance limitations exist due to a significant portion of non-parallel work.</p> Signup and view all the answers

    Which factor does NOT influence the parallel runtime of a program?

    <p>The amount of random memory access.</p> Signup and view all the answers

    What does wall clock time measure in a parallel computing context?

    <p>The elapsed time from the start to the finish of the overall process.</p> Signup and view all the answers

    In the context of a parallel processing system, which element is emphasized as critical to performance?

    <p>The combination of both algorithm and platform.</p> Signup and view all the answers

    Which of the following statements about performance metrics is false?

    <p>Parallel runtime is independent of the machine's communication parameters.</p> Signup and view all the answers

    What is the formula for calculating the speedup achieved after enhancement according to Amdahl's Law?

    <p>$ rac{Execution time_{old} - Execution time_{enhanced}}{Execution time_{new} - Execution time_{enhanced}}$</p> Signup and view all the answers

    Which of the following parameters is NOT required when applying Amdahl's Law?

    <p>The total execution time of the original program</p> Signup and view all the answers

    How is the overall speedup calculated when a fraction of the program is enhanced?

    <p>$Speedup_{overall} = rac{Execution time_{old}}{(1 - Fraction_{enhanced}) + rac{Execution time_{old}}{Speedup_{enhanced}}}$</p> Signup and view all the answers

    What does the 'Fraction enhanced' signify in Amdahl’s Law?

    <p>The portion of the program that benefits from the enhancement</p> Signup and view all the answers

    In Amdahl’s Law, what is implied if the speedup of the enhanced portion is very high?

    <p>Even with a high enhancement, overall speedup may be limited</p> Signup and view all the answers

    If the execution time of the old program is 100 seconds, and the enhanced part's execution time is reduced to 20 seconds with a speedup factor of 5, what is the fraction enhanced if the total execution time for the new program is 80 seconds?

    <p>0.75</p> Signup and view all the answers

    Which component contributes to the overall execution time in the Amdahl's Law formula?

    <p>The execution times of both enhanced and non-enhanced parts</p> Signup and view all the answers

    What is the implication of a 'Fraction enhanced' value of zero in Amdahl's Law?

    <p>There is no part of the program that can be enhanced</p> Signup and view all the answers

    Study Notes

    Amdahl’s Law

    • Amdahl’s Law calculates overall performance gains from speed enhancements in computer systems.
    • Performance improvement is limited by the fraction of time the improved function can be utilized.
    • Enhancements, like a faster floating-point unit, only reduce execution time for specific operations.

    Execution Time Calculations

    • Old Execution Time Formula:
      • Execution time old = Execution time non-enhanced + Execution time old-enhanced
    • New Execution Time Formula:
      • Execution time new = Execution time non-enhanced + Execution time new-enhanced
    • Execution time for non-enhanced components remains fixed, while enhanced execution time is reduced.

    Fraction Enhanced and Speedup

    • Fraction enhanced is calculated as:
      • Fraction enhanced = Execution time old-enhanced / Execution time old
    • Speedup after enhancement is given by:
      • Speedup enhanced = Execution time old-enhanced / Execution time new-enhanced

    Required Factors for Amdahl’s Law

    • Determine the computation time fraction that can leverage the enhancement.
    • Identify the speed improvement achievable by the enhanced execution mode for the entire program.
    • Overall speedup formula:
      • Speedup overall = Execution time old / [ (1 - Fraction enhanced) + (Speedup enhanced)]

    Example Calculation

    • For a Web server, enhancing the processor results in a 10x speed increase for computation, with the original processor busy 40% of the time.
    • Fraction enhanced = 0.4, Speedup enhanced = 10.
    • Overall speedup can be approximated:
      • Speedup overall ≈ 1.56; theoretical maximum ≈ 1.67.

    Analytical Modeling Basics

    • Sequential algorithms are evaluated by their runtime, typically as a function of input size.
    • Parallel runtime depends on input size, number of processors, and communication parameters.
    • Performance of a parallel system is influenced by both the algorithm and the underlying platform.

    Performance Measures

    • Wall clock time refers to the total time from the initiation of the first processor to the completion of the last processor in a parallel setup.

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    Description

    Explore the impact of Amdahl’s Law on the performance of computer systems with this quiz. Understand how improvements in specific parts of a system can influence overall efficiency. Test your knowledge on quantitative principles related to computer design.

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