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Re: Help: Install on AMD 64 creates display wash



Rory Gleeson wrote:
> I changed only AGP Mode to 4x and that booted me in!!! Woo Hoo!!!  BUT,
> shouldn't Fedora have been able to handle the 8x with this set-up?  Is this
> something worthy of Alan Cox's/Bugzilla time?  

I understand (from Dave Jones' writings) that 8x takes different
programming (it needs kernel attention). Last I heard, not all vendors'
AGP interfaces were supported at 8x.

No, I don't know why it didn't automatically drop back down to 4x. That
might even be a BIOS oddity (it's set to 8x So It Will Do 8x Or Die
Trying!)

Thanks for the hint, it's worth remembering.

> As well, If my ATI 9200se 128mb can handle 8x AGP, shouldn't my above settings
> actually be 8x and shouldn't I be able to change the Graphics Aperture Size to
> 128mb?  I don't know what either these settings actually means and the UG
> doesn't explain what any of these settings are are or what they do.  So, I
> need to be careful and fully informed as I move forward.
<snip>
>  I would think the 9200 128mb would have been sufficient.  Or maybe it's
> because my Graphics Aperture is set to 64mb??  I can set it as high as 256mb
> in the bios, but could my 128mb card handle that?  I'm not going to tweak
> these settings too much without advice, for fear that I blow something.

Going back to first principles, very briefly:

AGP was designed by Intel when 3D cards were new and the price of memory
was high. All graphics cards need memory to hold the frame buffer (which
holds the contents of the screen)[1]. 3D cards also need memory to store
textures[2], etc.

On PCI cards, those textures are copied across the PCI bus from main
memory into the card's memory, and used from there. AGP allows a card to
apply the textures directly from the computer's main memory[3].

Now if you have a 256 MB machine, and the program tries using most of
the 256 MB for memory, obviously there's going to be less for everything
else. AGP was largely aimed at gaming machines, which in 1998 meant
Windows 9x, which wasn't brilliant at memory management. So Intel came
up with the "AGP Aperture" which is, simply, the maximum amount of main,
system memory that AGP can use for texturing.[4]

If you're not doing 3D graphics, the aperture isn't even used, and its
setting is irrelevant. Even if you are, there's unlikely to be too
much difference between 64 MB and 256 MB.

So the 128 MB refers to your main memory, not the card's memory. And
you can quite happily set the aperture to 256 MB on a 128 MB system:
there's no danger of blowing anything. The worst that could happen,
which I've never seen, would be a system crash or a graphics crash.

And the first AGP graphics cards ran at 66 million transfers per second.
4x just means there are four times as many per second.

Notes:
[1] In games and other fast moving, high detailed visual programs,
there'll normally be two or more buffers to keep things smooth.

[2] Textures are pictures that are painted onto 3D objects. So you might
have a "wall" texture that is painted on a wall. As you move around, the
texture follows the wall, making it look as though the bricks in the
texture are part of the wall.

[3] Which turns out to be much slower: most graphics engineers and
programmers try pretty hard to avoid this in the first place.

[4] There's something called a GART that limits the requirement for
consecutive 4K pages, which makes this much easier.

HTH,

James.

-- 
E-mail address: james@ | "Face" on Mars proves to be optical illusion --
westexe.demon.co.uk    | NASA now investigating "vase" on Mars.




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