# What is “potential speedup” in parallel computing?

There is an example problem from p506 of Computer Organization and Design, Fifth Edition: The Hardware/Software interface by David A. Patterson, John L. Hennessy

I wonder how "potential speedup" is defined? The book doesn't give its definition.

In the example, since speedup with $10$ processors is $55\%$ of the potential speedup, the potential speedup should be $5.5 / 55\% = 10$. it is equal to the number of processors.

Since the execution time before improvement has a part $(10t)$ unaffectable by parallel computing on multiple processors, according to Amdahl's law (outlined in blue box), the potential speedup must be smaller than the number of processors.

So I am puzzled.

Google books has an earlier (4th) edition which has a similar example too.

• Don't use images as main content of your post. This makes your question impossible to search and inaccessible to the visually impaired; we don't like that. Please transcribe text and mathematics (note that you can use LaTeX) and don't forget to give proper attribution to your sources! – Raphael Jan 29 '15 at 17:53

Potential speedup $\equiv$ number of processors. I agree that it is poorly chosen wording. A better term would be efficiency (the average amount of time that the processors are doing useful work.)