Pointer Sizes
Pointers formats are known as near, far, or huge.
- Near pointers refer to the current segment, so neither DS nor CS must be modified to dereference the pointer. They are the fastest pointers, but are limited to point to 64 KB of memory (the current segment).
- Far pointers contain the new value of DS or CS within them. To use them the register must be changed, the memory dereferenced, and then the register restored. They may reference up to 1 MiB of memory. Note that pointer arithmetic (addition and subtraction) does not modify the segment portion of the pointer, only its offset. Operations which exceed the bounds of zero or 65535 (0xFFFF) will undergo modulo 64K operation just as any normal 16 bit operation. The moment counter becomes (0x10000), the resulting absolute address will roll over to 0x5000:0000.
- Huge pointers are essentially far pointers, but are normalized every time they are modified so that they have the highest possible segment for that address. This is very slow but allows the pointer to point to multiple segments, and allows for accurate pointer comparisons, as if the platform were a flat memory model: It forbids the aliasing of memory as described above, so two huge pointers that reference the same memory location are always equal.
Read more about this topic: Intel Memory Model
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