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With DPMI into protect mode and back | physical memory (Developers)

posted by ecm Homepage E-mail, Düsseldorf, Germany, 11.09.2010, 01:25

> That's exactly how things should NOT be - user having to work around
> application flaws coming from bad standards.
Agreed. It's your turn to travel back in time and establish better standards.

> It works even with XMS host (and maybe even EMM386 ???), [...]
It possibly doesn't work in EMM-remapped UMA space.

With an EMM, but no XMS available (maybe all allocated (maybe by the EMM)) you might go allocate some physical memory in VCPI then access that from the DPMI code. That's more cumbersome than with XMS but should still work.

> but there are only cca 1/2 MiB of low memory available,
I thought that was implicit when I said that DOS-handled memory can only sometimes solve this.

> [...], the other 64 KiB are wasted.
If you can re-use the space (partly), it's not (fully) wasted. Either the part behind or after the 64 KiB buffer will be at least 32 KiB large. Similarly, you can then re-use the remaining space in allocations of 16 KiB, 8 KiB, 4 KiB etc, alternating between the part behind and the one after the buffer as necessary. This requires little code and some pointers stored somewhere to reference where these data chunks are located. Some of these pointers or code could be stored in the "wasted" space, which still wastes some of the space but considerably less of it.

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l

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