Many Cores and the Limit on Speedup · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Why ten cores cannot always mean ten times

Computing · Computer Systems · ages 19-20
Name ______________________   Date ____________

  1. What sets the ceiling no core count can lift?

    • Serial work
    • The fan noise
    • The screen size

  2. A tenth of a program is serial. What is the top speedup?

    • Ten times
    • A hundred times
    • Endless times

  3. Data lanes and cores are the same tool.

    Circle one:   True   False

  4. Code marches 8 numbers through one step together. Which tool is it using?

    • A faster clock
    • Data lanes
    • A bigger disk

  5. A tenth serial program runs on nine cores. Type the speedup.

    Answer: ______________

  6. Doubling cores slowed a program. What best explains it?

    • Cores dislike even numbers
    • The code ran too early
    • Overhead outgrew the gain

  7. Buying cores always pays once a program is half parallel.

    Circle one:   True   False

  8. A buyer adds cores past 100 to a tenth-serial program and expects 100 times. What is the flaw?

    • Cores past 100 switch off
    • The serial cap still holds
    • Serial code runs backwards
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Why ten cores cannot always mean ten times W1-mt_dy3-K9dV19-s1

  1. Serial work · Ordered work must run in order.
  2. Ten times · One divided by one tenth is ten.
  3. False · Cores split tasks; lanes march numbers together.
  4. Data lanes · One step over many numbers is lane work.
  5. 5 · One tenth plus nine tenths over nine is two tenths, inverted to five.
  6. Overhead outgrew the gain · Overhead can dwarf parallel gain.
  7. False · Overhead can still eat the gain.
  8. The serial cap still holds · No core count lifts the serial ceiling.
Worksheet · LightMySky