On Sat, 12 Feb 2022 at 01:52, Travis Siegel <tsie...@softcon.com> wrote:
>
> Not true.
Sometimes true.
> If both of the partitions are primary partitions, and the bootable flag is
> swapped from one to the other, then when one boots, the second will be drive
> d:, and vice versa.
It depends on the OSes in use.
The formal DOS schema is:
[1 primary and then one extended containing multiple logical drives] x per drive
Letter allocation is complicated:
DOS and DOS-based OSes:
[1] iterate through physical drives assigning letters to primary
partitions in drive order, starting at C
Then
[2] iterate through all logical drives on each drive assigning letters
So if there is:
1:[(primary){extended(logical 1)(logical 2)}]
2: [(primary){extended(logical 1)(logical 2)}]
Then you will get this:
1:[(primary C:){extended(logical 1 E:)(logical 2 F:)}]
2: [(primary D:){extended(logical 1 G:)(logical 2 H:)}]
Drive letters are not in physical drive sequence.
Note: there is only 1 permitted primary per drive.
If you have >1 visible primary per drive, Win NT 3-4 would fail with a BSOD.
Win95B and on, which support FAT32, might handle it, but might also
fail to boot. I've never managed to pin down all variations.
Win2K could handle it but would BSOD if the partitions were not in
numerical order:
1:[(primary){extended(logical 1)(logical 2)}] <- fine, works
1:[(primary){extended(logical 2)(logical 1)}] <- BSOD on boot-up
XP could handle it.
Vista and on dump all the old DOS-based logic and use a new system.
But DOS is tricky these days. Many people have extracted "MS-DOS 7.1"
from Win98 and use it standalone. I *think* these variants *can*
handle >1 visible (unhidden) primary, but I have a suspicion that the
old FAT16-only versions can't.
But you're not meant to do this; it wasn't in the DOS design.
Additional primaries were for non-DOS OSes with formats that DOS can't
read: back then, Netware, Xenix, etc.
It may work in later versions, but I advise against totally relying on it.
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