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Partitioning of 4TB HDD for legacy OSes (Users)

posted by mceric, Germany, 28.04.2026, 01:35

Hi!

> Physical drive #1 geometry LBA sectors: 3519069872 (1803 GB), sector=512 B
> As you can see LBA sectors: 3519069872 (1803 GB) instead of real
> drive capacity that is exactly 7814037168 sectors. So it's an evident EDD
> bug - 7814037168 mod 2^32 = 3519069872 so BIOS do only 32b arithmetics...
In theory, int 13, ah=48h, dl=drive, ds:si pointer to buffer is supposed to return a 64-bit value at offset si+10h. I can easily imagine a BIOS failing to return all bits here, though. Which tool did you use to view the EDD data?

> Then need to deal with 2TB MBR barrier...
As people already started to work on this, I suggest to contribute to DOS GPT support if you really want > 2 TB for DOS.

Does hybrid GPT-MBR really work? Or is the MBR on a GPT disk just a dummy to keep non-GPT OS from causing problems?

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FreeDOS / DOSEMU2 / ...

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