Page size, internal fragmentation, I space, D Space, mapped file

Internal fragmentation: Internal fragmentation refers to the wasted space in a page. For s segments in memory with a page size of p bytes, sp/2 bytes will be wasted on internal fragmentation. For average process size a bytes and if each page entry requires b bytes, then,

Approximate number of pages needed per process = a/p

Page table space occupied = ab/p

Wasted memory in last page of the process due to internal fragmentation = p/2

Total overhead = ab/p + p/2


p = sqrt(2ab)

In some 16 bit computers there are separate address spaces for instructions and data.

I space: It is a separate address space for program text and instructions.

D Space: It is a separate address space for data.

Mapped file: A process can map a file in its virtual address space for I/O. Two or more processes can map the same file. When they have mapped a file processes can communicate over shared memory.

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