SWAPPING

  • Swapping is a technique of removing a process from main memory and storing it into secondary memory, usually a hard disk temporarily and then bringing it back into main memory for continued execution.

  • Swapping is a memory management technique used in multiprogramming environments which have limited memory capacity.

  • Thus, in Multiprogramming swapping may be used to increase the number of process sharing the CPU.

  • However, in Multiprogramming, there may arise a situation when all the active processes cannot be accomadated in the main memory.

  • In this case, one of the process may be moved out temporarily from main memory to secondary memory so as to create a sapce for another active process.

  • This action of moving a process out of main memory is called Swap out and the action of moving a process into the main memory is called swap in.

  • The area on the disk where the swapped out processes are stored is called Swap Space.

  • Backing store is a usually a hard disk drive or any other secondary storage which fast in access and large enough to accommodate copies of all memory images for all users. It must be capable of providing direct access to these memory images.

  • Swapping concept comes in terms of process scheduling.

  • Swapping is basically implemented by Medium term scheduler.

  • Medium term scheduler removes process from CPU for duration and reduce the degree of multiprogramming.

  • And after some time these process can again be reintroduced into main memory.

  • Swapping can be implemented in various ways. For example, swapping can be priority based. That means if a higher priority process arrives and wants service, the memory manager can swap out the lower priority process to the secondary memory so that it higher priority process can be loaded to main memory for execution.

  • As soon higher priority process finishes, the lower priority process will be swapped back to main memory and execution will be continued. Sometimes swapping is also called roll out, roll in.

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