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Concept of Virtual memory in Microcontroller

The term 'virtual' refers to something which appears to be present but actually it is not. The virtual memory technique allows users to use more memory for a program that the real memory of a computer. A programmer can write a program which requires more memory space than the capacity of the main memory. Such a program is executed by virtual memory technique and the program is stored in the secondary memory.

The memory management unit (MMU) transfers the current needed part of the program from the secondary memory to the main memory for execution. This part of the program is executed by the processor. After execution, this part of the program is sent back to the secondary memory together with the intermediate results. Thereafter, the CPU takes another part of the program for execution. Thus, the main memory always keeps only the currently needed part of the program.

This type of 'to and fro' movement of instruction and data between the main memory and the secondary memory is called swapping. Thus, a program requiring more memory space than the capacity of the main memory can be executed using swapping technique. This concept is virtual memory technique. The maximum capacity of the virtual memory of a computer system is dedicated by the processor hardware.
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