David Niemi wrote: > Just to intrude another question along similar lines: what about for > those systems with an AGP or PCI(-X) card that have their own RAM and > there is also a similar amount of system RAM alocated to AGP/PCI > graphics called "AGP Aperature Size" or similar in the motherboard's > BIOS. To the best of my knowledge, this doesn't affect normal PCI cards, just PCI Express (which is not PCI-X) and AGP. (I doubt it affects PCI-X: PCI-X is aimed at different uses). Modern 3D graphics cards use video for the frame buffer (what's being shown on the display), 3D calculations (especially the Z-buffer, which records how far "into" the picture some 3D object in, and hence whether another 3D object will be in front of it and so should overdraw it), and the textures that are painted onto the 3D objects. So if you have a brick wall, what makes it look like it's made of brick is a brick texture applied to the wall. Textures can take up a lot of memory. On PCI graphics cards, all textures had to be copied to the graphics card memory before they could be used. This limited the amount of textures that could be used. An AGP card can keep textures in main memory, and render them directly onto the frame buffer. This is faster than copying it into the card's memory and then using it, but slower than just having it in the card's memory anyway. There is something called a GART (Graphics Address Remapping Table) that tells the graphics card where the textures are kept in main memory. And the Aperture Size is the maximum amount of textures to which this can refer: the maximum amount of memory that can be used for textures and not for running the rest of the system. It is a maximum: when it's not needed, the memory is available for other purposes. It doesn't have to be the same size as video memory: that's merely due to the relative sizes of graphics card memory and main memory on modern systems. James. -- James Wilkinson | Watch your grammar, teams: the double negative is a Exeter Devon UK | complete no-no. E-mail address: james | -- "I'm Sorry, I Haven't A Clue", BBC Radio 4 @westexe.demon.co.uk |
