Swapping - Technique used to temporarily remove non-active programs from memory

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• Nirja Shah   -Posted on 25 Nov 15
  Swapping
  - It is the technique of temporarily removing the inactive programs from the memory of a computer system.
  
  - An inactive program is the one which is neither executing on the CPU, not performing an I/O operation.
  
  - The programs existing in the memory are classified into three categories:
  
  1. Active programs - One active program executes on the CPU while others perform I/O.
  
  2. Programs being swapped out of the memory.
  
  3. Programs being swapped into the memory.
  
  - Whenever an active program becomes inactive, the OS swaps it out by copying its instructions and data onto a disk.
  
  - A new program is loaded in its place.
  
  - The new program is added at the end of the scheduling list; it receives CPU attention in due course.
  
  - Use of swapping is feasible in time sharing systems because the time sharing kernal can estimate when a program is likely to be scheduled next.
  
  - It can use this estimate to ensure that the program is swapped in before its turn on the CPU.
  
  - Swapping increases the OS overhead due to the disk I/O involved.

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