33 Coverage and Exchange

Covering and swapping: Covering and swapping techniques are two methods used to expand memory in a multi-program environment.
1. Covering: Because the program and data are not accessed at all times when the program is running, the user space can be divided into One fixed area and several coverage areas. Put the active part in the fixed area, and segment the rest according to the calling relationship. First put those segments that will be accessed into the coverage area, and put other segments in the external storage. Before calling, the system will transfer them into the coverage area to replace the original segments in the coverage area.
2. Exchange: Move the program in the waiting state from the memory to the auxiliary memory to free up space. The process of moving programs that are ready to compete for CPU operation from auxiliary storage to memory is called swap-in. Intermediate scheduling is to use switching technology.