Overlay in Memory Management

Overlay in memory management:

Overlay is a technique to run a program that is bigger than the size of the physical memory by keeping only those instructions and data that are needed at any given time.

Divide the program into modules in such a way that not all modules need to be in the memory at the same time.

The main problem in Fixed partitioning is the size of a process has to be limited by the maximum size of the partition.

Overlay is a solution for such problems.

The concept of overlays is that whenever a process is running it will not use the complete program at the same time, it will use only some part of it.Then overlays concept says that whatever part you required, you load it an once the part is done, then you just unload it, means just pull it back and get the new part you required and run it.


“The process of transferring a block of program code or other data into internal memory, replacing what is already stored”.
Sometimes it happens that compare to the size of the biggest partition, the size of the program will be even more, then, in that case, you should go with overlays.

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      1. Andrew S. Tanenbaum, David J. Wetherall, “Computer Networks” Pearson Education.
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      3. KavehPahlavan, Prashant Krishnamurthy, “Networking Fundamentals”, Wiley Publication.
      4. Ying-Dar Lin, Ren-Hung Hwang, Fred Baker, “Computer Networks: An Open Source Approach”, McGraw Hill.