What are near, far and huge pointers?

Question

Can anyone explain to me these pointers with a suitable example ... and when these pointers are used?

Answer 1

In some architectures, a pointer which can point to every object in the system will be larger and slower to work with than one which can point to a useful subset of things. Many people have given answers related to the 16-bit x86 architecture. Various types of pointers were common on 16-bit systems, though near/fear distinctions could reappear in 64-bit systems, depending upon how they're implemented (I wouldn't be surprised if many development systems go to 64-bit pointers for everything, despite the fact that in many cases that will be very wasteful).

In many programs, it's pretty easy to subdivide memory usage into two categories: small things which together total up to a fairly small amount of stuff (64K or 4GB) but will be accessed often, and larger things which may total up to much larger quantity, but which need not be accessed so often. When an application needs to work with part of an object in the "large things" area, it copies that part to the "small things" area, works with it, and if necessary writes it back.

Some programmers gripe at having to distinguish between "near" and "far" memory, but in many cases making such distinctions can allow compilers to produce much better code.

(note: Even on many 32-bit systems, certain areas of memory can be accessed directly without extra instructions, while other areas cannot. If, for example, on a 68000 or an ARM, one keeps a register pointing at global variable storage, it will be possible to directly load any variable within the first 32K (68000) or 2K (ARM) of that register. Fetching a variable stored elsewhere will require an extra instruction to compute the address. Placing more frequently-used variables in the preferred regions and letting the compiler know would allow for more efficient code generation.