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#### Mem; Port; Ptr; Seg; Ofs; PrefixSeg; etc.

Those few routines in the `System` unit that deal with segmented pointers (e.g., `Ptr`) are emulated in such a way that such ugly BP constructs like

    PInteger (Ptr (Seg (a), Ofs (a) + 6 * SizeOf (Integer)))^ = 42

work in GPC, but they do not provide access to absolute memory addresses. Neither do `absolute` variables (which take a simple address in the program's address space in GPC, rather than a segmented address), and the `Mem` and `Port` arrays don't exist in GPC.

As a replacement for `Port` on IA32 processors, you can use the routines provided in the `Ports` unit, Ports. If you want to access absolute memory addresses in the first megabyte under DJGPP, you can't do this with normal pointers because DJGPP programs run in a protected memory environment, unless you use a dirty trick called near pointer hack. Please see the DJGPP FAQ (see DJGPP FAQ) for this and for other ways.

For similar reasons, the variable `PrefixSeg` in the `System` unit is not supported. Apart from TSRs, its only meaningful use in BP might be the setting of environment variables. GPC provides the `SetEnv` and `UnSetEnv` procedures for this purpose which you can use instead of any BP equivalents based on `PrefixSeg`. (However note that they will modify the program's own and its childs' environment, not its parent's environment. This is a property - most people call it a feature - of the environments, including DJGPP, that GPC compiled programs run in.)