17. FIFO Page Replacement
The chapter covers various page replacement algorithms used in operating systems, emphasizing the mechanics and effectiveness of FIFO, Optimal, and LRU strategies. It addresses the challenges and solutions surrounding these algorithms, particularly in tracking page usage to minimize page faults. It also discusses approximation techniques for LRU and introduces the modified clock replacement algorithm, highlighting their practical applications and limitations.
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What we have learnt
- The FIFO algorithm replaces the oldest page in memory regardless of its usage.
- The Optimal Page Replacement algorithm gives the best possible fault rate but is impractical as it requires knowledge of future requests.
- The Least Recently Used (LRU) algorithm is a better approximation for replacement based on past usage but requires special tracking mechanisms.
Key Concepts
- -- FIFO
- First-In-First-Out is a page replacement algorithm that replaces the oldest page in memory.
- -- Optimal Page Replacement
- This algorithm replaces the page that will not be referenced for the longest time in the future, minimizing page faults but impractical to implement.
- -- Least Recently Used (LRU)
- An algorithm that replaces the page that has not been accessed for the longest time in the past, based on usage history.
- -- Dirty Bit
- Indicates whether a page has been modified (written to) and needs to be saved to disk before replacement.
- -- Clock Algorithm
- An approximation of LRU that gives pages a second chance for retention if they have been recently used.
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