Total speedup from parallel effort is capped by the fraction of work that cannot be parallelised.
If 5% of a task is strictly serial, twenty processors yield a theoretical speedup of about 10.3 times, and even infinitely many processors cannot exceed twentyfold. The same arithmetic caps what adding people to a project can achieve.
In practice
- A support team automates 80% of ticket triage and finds handling time barely moves, because the manual 20% was always the slow part.
- Ten people cannot review a document four times faster than four people if the final sign-off is one person.
- Further reading
- Wikipedia
- Subject
- Organizations & Bureaucracy
- Essay
- How organisations behave when nobody is steering