SLI - old 3dfx way & new nvidia way

[imported_hopeless]

I don't know if maybe I've overlooked something, but I have read about the way nvidia is working on sli. Thet have two different rendering methods, which need to be tested to see which will work best for each game. Since they bought 3dfx was/is there something bad about the way they did it back then, just splitting the screen between odd & even lines?

 

[sparkyclarky]

AFAIK, the splitting odd and even lines doesn't result in the same balanced load that NVs new process does. SLI is naturally the most efficient if you can get each individual GPU to take up 50% of the rendering. With the complexities in rendering modern games, I'm guessing that an odd/even split doesn't necessarily result in a very even load balance. But, I could be wrong.

 

[nRollo]

The old alternate line way resulted in an image some deemed grainier. It was noticeable. (but still the thing to have- then and now!)

 

[Schadenfroh]

the thing that makes it so much better is the improved load balancing and that it is digital sli

 

[Rand]

Originally posted by: hopeless
Since they bought 3dfx was/is there something bad about the way they did it back then, just splitting the screen between odd & even lines?

All 3dfx's cards and the implementation did was rasterise textured triangles.
Simple, and straightforward to divide the rendered scene up by scan lines. Easily used on any application across any number of chips.

nVidia could potentially have used a similar implementation but then VS/PS performance wouldn't scale at all, in fact it would be slower in an SLI system with the added overhead.
Clearly we're not about to go back to relying on the processor to do all the geometry work as we did in the Voodoo 2 SLI days and the Voodoo 5, and we obviously don't want to hamper VS/PS throughput at all in an SLI implementation as a GPU's geometry performance is becoming even more important then sheer pixel/texel fillrate in todays applications.

nVidia wants to scale geometry throughput as well as pure rasterization speed, so they need to ensure both GPU's are not calculating the same geometry workload. You can't do that if your dividing by scan lines, as 3dfx did so their stuck with splitting top/bottom half of the screen (Split Frame Rendering/SFR) which is the preferable solution.
It scales the best, but unfortunately it's not compatible with all games depending on rendering techniques used.
They can also use Alternate Frame Rendering (AFR) much the same as ATi did with the Rage Fury Maxx, a viable option though it doesn't scale quite as well as SFR, and it also doubles latency so response time to user actions is cut in half. It is more broadly compatible with applications then SFR however, though there will still be some games in which you'll have to resprt to single GPU mode due to compatibility issues.

The old alternate line way resulted in an image some deemed grainier. It was noticeable. (but still the thing to have- then and now!)

That was primarily due to the pass through cable, nVidia isn't using that so they likely could have used 3dfx's implementation with no impact on image quality at all.
As said, it's not a particularly ideal solution though as geometry performance wouldn't scale at all.... not a big deal in older games and even many current ones but is becoming an increasingly major factor in GPU performance.
The lone plus side to 3dfx's implemtnation is it would be easily compatible with any games though, which won't be true for nVidia's implementation unfortunately.

 

[Xionide]

LONG LIVE VOODOO!

 

[nRollo]

I almost forgot!

I have two 12 MB Creative V2s and SLI cables in storage for the day we all return to Glide!

I could put them in, put the pass through on the XT PE, and be livin large like the big dogs! SLI Jr.

 

[venk]

IIRC the 3dfx meathod renderd half the screen with each card. It was fairly ineffeicent because the top half of the screen generally contained much less graphic data than the bottom in most games.

 

[dug777]

Originally posted by: Rollo
I almost forgot!

I have two 12 MB Creative V2s and SLI cables in storage for the day we all return to Glide!

I could put them in, put the pass through on the XT PE, and be livin large like the big dogs! SLI Jr.

can u do that/has ne one tried it? I guess u'd get massive driver problems(having run a v2 12mb 4 a year or so with windows xp & a 400mhz celeron/sis620- managed 2 get GTA3 running on it!) and if it did work, big time slo-down...

 

[sparkyclarky]

Originally posted by: venk
IIRC the 3dfx meathod renderd half the screen with each card. It was fairly ineffeicent because the top half of the screen generally contained much less graphic data than the bottom in most games.

it was alternate lines (at least for the V2), but that may have been the case for the VSA chips?