Why does the page-replacement code check the modify (dirty) bit of a victim page?
Correct answer B. A page that has not been modified need not be written back to disk before its frame is reused
Explanation
The hardware sets the modify bit when a page is written. If a victim page's bit is clear, its copy on disk is still current, so the frame can be reused at once, saving one disk write and halving the cost of that fault. Recency of use is tracked by the reference bit, which LRU approximations such as the clock algorithm rely on.
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