These are some old concepts used in 16 bit intel architectures in the days of MS DOS, not much useful anymore.

Near pointer is used to store 16 bit addresses means within current segment on a 16 bit machine. The limitation is that we can only access 64kb of data at a time.

A far pointer is typically 32 bit that can access memory outside current segment.  To use this, compiler allocates a segment register to store segment address, then another register to store offset within current segment.

Like far pointer, huge pointer is also typically 32 bit and can access outside segment. In case of far pointers, a segment is fixed. In far pointer, the segment part cannot be modified, but in Huge it can be

See below links for more details.

http://www.answers.com/Q/What_are_near_far_and_huge_pointers_in_C

https://www.quora.com/What-is-the-difference-between-near-far-huge-pointers-in-C-C++

http://stackoverflow.com/questions/8727122/explain-the-difference-between-near-far-and-huge-pointers-in-c

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