A concept found in page swapping algorithms. When using a first-in-first-out method of page swapping, if you increase the number of frames, it is possible that it will increase the number of page faults. This is contrary to the intent of adding more frames, thus the anomaly. This is one reason why a FIFO approach is not recommended.

As an example, take the following list of page references: 123412512345212345.
Here are the frame contents with three frames*:


Now here are the contents with four frames:

So there are fourteen page faults with three frames, but fifteen with four frames. This does not happen with the least-recently-used approach.**

*Emphasized frames represent page faults.
**Incidentally, the lru algorithm for this set of page references would result in 15 page faults with three frames and 12 page faults with four frames.

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