DSA Factory
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Operating systems

Free Virtual memory lessons

7 lessons, about 1½ hours in all. Each teaches one idea with a visual, then gives you a problem or a few questions on it. Read the lessons here, then create a free account to practise and keep your progress.

Start free with lesson 1See the full Virtual memory path

Stage 0Demand paging

  1. Why virtual memorySee how running programs bigger than RAM works, and what else the same mechanism gives you.12 min
  2. Page faultsFollow a page fault from the hardware trap to the restarted instruction.12 min
  3. What a page fault costsCalculate effective access time with page faults, and see why the fault rate must be tiny.12 min

Stage 1Page replacement

  1. Choosing which page to evictCompare FIFO, LRU and the optimal policy on a reference string, and see how far each is from the best.15 min
  2. Belady's anomalySee a case where giving FIFO more memory makes it fault more, and why LRU can't do that.11 min
  3. Approximating LRU: the clock algorithmUse one reference bit per page and a sweeping hand to get most of LRU's benefit at almost no cost.13 min

Stage 2Thrashing and the working set

  1. Thrashing and the working setSee why a process with too few frames spends its time faulting, and how the working-set model sets the right number.14 min

All of Virtual memory is free

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