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 :)

Comments

OT: SiS rocks

[Toasty16]

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.

Re:OT: SiS rocks

[rabidcow]

SiS has been around for a LONG time, tho probably not doing chipsets. I've got an old Hercules monochrome clone here with a bunch of large chips marked "SiS". (dated 8804)

But I had a MB based on the SiS 530 chipset and it was nasty. It was basically a cheapo bargain board. It sounds like they've improved substantially since then.

my Tribes2 + X

[Trevelyan]

I have a ATI AIW 32MB DDR, and my tribes2 can get a lil laggy esp when their are some vehicles on my screen.
reading my X log I notices that DRI was using 1X mode for AGP. after some RTFM, I found the option to kick it into 4x.
Anyway the point being it didn't help speed up the game gfx (well i didn't notice much difference)

In case ur wondering for ATI cards the XF86Config option is:
Option "AGPMode" "4"

Also i noticed:
Option "AGPSize" "32"
But i cant tell if setting this bigger then the ram on the card helps or not (maybe that the buffer size opt?), was hoping to let the card borrow more of my sys ram (which is pc100, slow compared to gfx cards DDR, but better then hdd =)
anyone know any other good opts to help eek more speed?

Re:AGP4x VS AGP8x.

[jtdubs]

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

Re:OT: SiS sucks rocks

[Reziac]

SiS has been doing motherboard chipsets since at least the 486 era, and I/O cards before that. I've also had SiS-based motherboards, and they had bugs and instabilities I'd never even heard of before. I've long since come to associate SiS chipsets with the mobo mfgr cutting corners, and haven't seen anything yet to make me change my mind. (Tho the SiS-based I/O cards for 386/486 machines seemed to be pretty good in their day.)

As to another poster who says he likes SiS because of the "low heat/low power" ... gee, I wonder if that's why SiS chipsets need heatsinks, even when no other chipset in the same class needs 'em.

Re:AGP8X

[Saeger]

Yeah, it's called foveation, but we can't use it effectively because eye tracking hardware isn't cheap enough or accurate enough.

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