What is Virtual Memory?
The term
virtual memory 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 than the real memory of a computer. So,
virtual memory is the concept that gives the illusion to
the user that they will have main memory equal to the capacity of secondary
storage media.
Need of Virtual Memory
Virtual
memory is an imaginary memory, which we are assuming. 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. The program is stored in the secondary memory. The memory
management unit (MMU) transfers the currently needed part of the program from
the secondary memory to the main memory for execution. Movement of instructions
and data (parts of a program) between the main memory and the secondary memory is
called Swapping.
Address space and Memory Space
Virtual
memory is the address used by the programmer and set of such addresses is
called address space. An address in main memory is
called location or physical address. The set of such
locations in main memory is called memory space or physical
Memory (RAM). Thus, the memory space consists of the actual main
memory location directly addressable for processing.
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