OT: PC VGA

[Fredrik Tolf]

Hi all!

My apologies for posting off-topic to this list, but I really can't
think of whither I *should* turn this question, and I think there
ought to be people here in the know.

The thing is, I've been wondering for the longest time how PC VGA
really works. In particular, I'd like to know the mechanism that
allows some random PCI card to be accessed through the standard VGA
register addresses (0x3c0 and its ilk) and likewise for the VGA BIOS
and the real mode "framebuffer" memory mapping, and also what software
entity that sets that stuff up. Any links would be highly appreciated!

The practical reason why I'm wondering these things is because I'm
using several video cards in one of my computers, with one X.org
server for each card, and every once in a while, it causes problems
which I'm guessing is because one of the "secondary" (non-VGA-mapped)
card's BIOS is trying to access the card through the normal VGA ports
and accidentally hitting the VGA-mapped card. I am also more generally
curious about what it takes to use several video cards independently
on today's machines. But I'm holding a general interest in these
things, so I'm not just wondering for pragmatical reasons.

Also, in general -- are there any good web resources for these sorts
of things (hardware standards in general)? I've been googling around
quite a bit without being able to find anything good.

I'd appreciate any replies!

Fredrik Tolf