Subject: Re: PNP BIOS brokenness and proposed fix
To: Rafal Boni <>
From: Todd Whitesel <>
List: port-i386
Date: 11/01/2000 00:05:34
> 	The short of the story is: on my GW, the PNPBIOS would occasionally 
> 	find the need to refer to data in the `Extended BIOS Data Area' (at
> 	0x400 in physical memory, 0040:0000 in the wonderful x86 segmented
> 	`architecture' 8-) from within the PNPBIOS code... 

I think you will find in various "undocumented PC" references that this
segment is basically required to be hardcoded because of all the PC code
that assumes it, dating back to the original days of real mode where it
actually did refer to 0x400 linear -- just after the interrupt vectors.

It is practically part of the PC BIOS architecture that this segment has
to be reserved. Barf-worthy to be sure, but I've had to ship code (for
16-bit windows, note) that made this assumption -- no API was provided
to access that information, so you just had to hope that the segment worked,
or somehow convince the system to give you one pointing at the same address.

Todd Whitesel
toddpw @