Free Virtual memory lessonsVirtual memory · Stage 1 · Page replacement · Step 3
Approximating LRU: the clock algorithm
Use one reference bit per page and a sweeping hand to get most of LRU's benefit at almost no cost. About 13 minutes.
In the clock algorithm, the hand points at a page whose reference bit is 1. What happens?
- AThe bit is cleared and the hand moves on: the page gets a second chance
- BThe page is evicted
- CThe page is kept for ever
Show the answer
The bit is cleared and the hand moves on: the page gets a second chance. It has been used recently, so it isn't evicted yet.
4 questions on this idea
Short questions that apply the idea to new cases: trace it, work out a number, put steps in order. A wrong answer explains itself.
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