Why is mapping required? Computer 'Paging' & 'Segmentation'.

Answer Posted / vikram

virtual address concept allows a operation system to execute
a process without having the entire process in the main
memory. That is you have only a part of the process which is
just enough for execution at that point of time. But from
the computers point of view it is thinking that the entire
process is available in the memory. To make this work we
make believe the computer with a bigger memory say 2gb
virtual memory but you are having only 1 gb physical memory.

now the computer as usually tries to get a part of the
process in the the cpu for execution. But the part requested
may be present in the main memory or not because we have
bluffed the computer by giving virtual address. So in
situation where we have the part in main memory we have to
give the computer with that physical address.

so the procedure which gives the physical address from its
virtual address is called paging.


Segmentation is totally a different concept. A segment would
comprise of a function that you have written in your code.
In this case to refer to a function you have to refer to
that function and then to the page that has this segment.
This concept is called segmented paging.

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