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AGP4X vs. AGP8X
An anonymous reader writes "With upcoming chipsets such as the SiS648 claiming support for the latest AGP8X standard, we asked ourselves if there were any performance benefits. We took the SiS648 and Xabre 400 reference boards, modified them and compared the results." I can't even get 4x stable under XP, so I figure 8x is
half as likely to let me play NWN :)
Basically, SiS has come out of nowhere with motherboards that absolutely trash the competition in regards to performance and features. It started last year with the SiS 735, the best performing Athlon mobo of the year. Sadly, it was a poor overclocker, so it was shunned by AMD fans. But this year SiS has had a string of hits. It's the only 3rd party with a P4 license, which makes it the only choice for mobo manufactures in terms of 3rd party P4 mobos (obviosuly they're ansty about Intel frowning upon their Via-based P4 boards, seeing as Via doesn't have a valid P4 license). The SiS 645, 645DX, and now the 648 have consistently been of high quality with features no one else has. The 645 introduced MuTIOL which doubled the bandwidth between north and south bridges, to 533MB/s. The 645DX introduced unnofficial, rock solid DDR400 support. Now the 648 again doubles bandwidth between north and south bridges to 1 GB/s, it introduces AGP 8x, and it probably will officially support DDR400. SiS 648 boards also have Serial ATA support. This is a far cry from a decade ago, when everyone knew SiS=shit.
With 3D Games, screen resolution isn't really an issue. The screen resolution and how much you need to saturate the AGP bus are completely independant. The only thing that determines the AGP bus saturation is how much geometry you need to send and how efficiently you can send it. How many textures you need to send and how efficiently you can send them.
With texture memory creeping upwards in 3D cards we should eventually see a point where all textures can be stored on the card and sending textures over AGP should be rare.
However, sending geometry is usually done per-frame in most 3D games, and you'd be surprised how much all of those triangles can add up.
1M triangles, with 3 vertecies, 3 texture coordinates, 3 normal vectors and sometimes more per vertex with each vector being comprised of 4 floats and each float of 4 bytes.
1,000,000 * (3 + 3 + 3) * 4 * 4 = 144,000,000
That's 144MB per frame. At 60 frames per second that's 4.22GB per second.
Now, granted, 1M tris per frame is way high for today's games. Most current games push around 30k per frame, never more than 60k. My friend and I are doing closer to 300k and are already starting to become AGP-bandwidth-limited.
Anyway, you are right. You can't have too much bandwidth to your video card. I'd love to be able to push a full 1M tris/frame, and I'm sure I will be able to soon. Just not yet. And not even with AGP 8x in all likelyhood.
Justin Dubs