Belady’s anomaly occur while FIFO Page Replacement Policy - Operating System

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• Nirja Shah   -Posted on 12 Nov 15
  Bélády's anomaly
  - It is the name given to the phenomenon where increasing the number of page frames results in an increase in the number of page faults for a given memory access pattern.
  
  - It is mostly experienced while using the First in First Out (FIFO) page replacement algorithm.
  
  - It was demonstrated in 1969 by László Bélády.
  
  - The information is loaded in specific chunks using the common computer memory management.
  
  - Each chunk is referred to as a page.
  
  - At a time only limited pages can be held by the central processor.
  
  - A frame is required by each page to load.
  
  - A page fault occurs when a page is not found, and might need to be loaded from disk into memory.
  
  - Whenever a page fault occurs and all the frames are in use, one must be cleared to make space for the new page.
  
  - A simple algorithm is FIFO: whichever page has been in the frames the longest is the one that is cleared.
  
  - It was always believed that an increase in the number of page frames would always result in the same number or fewer bpage faults unless the Bélády's anomaly was demonstrated.
  
  

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