AP CSP Day 53: Parallel Computing Speedup
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Big Idea 4
Day 53 Practice
Focus: Parallel Computing Speedup
Practice Question
A task takes 60 seconds on one processor. Using 3 processors working in parallel, it takes 25 seconds. What is the speedup?
Why This Answer?
Speedup = sequential time ÷ parallel time = 60 ÷ 25 = 2.4. Less than ideal 3× because of overhead and dependencies.
Why Not the Others?
A) This would be 35 ÷ 25.
C) This would be 3 processors with perfect scaling (no overhead).
D) This is the time saved, not speedup.
Common Mistake
Watch Out!
Confusing speedup with number of processors. Speedup = time ratio, usually less than processor count due to overhead.
AP Exam Tip
Speedup = sequential_time ÷ parallel_time. Perfect speedup = processor count, but overhead reduces this.