[Drakkon]

I feel like i have fallen behind on the times...I started looking for some new parts and i see all this hype about SLI systems. So i got a couple questions...
What exactly is SLI? Is there any site out there that describes what it is and what it can do?
Are there specific video cards you have to buy with an SLI board? Can i go ATI or Nvidia or am i stuck to nvidia? (it seems like it since every review uses nvidia cards so far)

[ivwshane]

Do you remember the old voodoo cards where you could connect two cards together to get more performance? It's the same thing.

[Mince]

Right now Nvidia is the manufacturer of SLI technology...ATI has the same thing , i dont know if it is out yet...but it is called Crossfire...

If you go to Alienware website you can view a video that explains this technology...

But ivwshane is correct, it is just get higher performance.

[Drakkon]

hmmm so how it looks from reviews of "sli" cards you get maybe a 40-50% gain? not a true 100% gain?

[hans5849]

not untill you hit the higher resolutions with AA/AF

Anandtech BF2 comparison

[Bear]

There is no TRUE 100% performance increase but 40-50% is about right.

Basically how SLI works is, you have 2 video cards in PCI-E slots connect by a bridge. The each card renders half of the screen. I'm assuming bottom for bottom, top for top. Doesn't matter.

Obviously, the stress to render half the load allows for better performance from one video card. While it's a good technology, it's still in its prime. You still can only use the exact same cards together. No mixing and matching Leadteks with eVGAs. (some cards can be mixed matched but they must be identical in terms of video BIOS and specs)

The only really Pro I can think of would be the performance. In my opinion, the cons weigh out the pros.

Cons:

- 2 cards can be pricey
- Some games have issues running with V-sync enabled on SLI
- Still in its first generation, meaning it has a few driver updates to go before it's fully stable (IMO)
- Most likely in 6 months from purchasing the best SLI setup, you'll be beat out by 1 card that's next gen.

Bottom line:

Get it if money is of no concern. Otherwise, I really wouldn't recommend it.

[Drakkon]

makes sense now or actually made sense when mentioned the ol vodoo cards...
I did actually catch the article somewhere that said how a dual 6800 system is not being beat outby 1 7800GTX OC system.
So it looks like purchasing a SLI mobo is a good idea if you got money to waste, otherwise a regular board will be just fine? I'd go socket 939 no matter what since that seems to be the way chips are going but just hoping to get a board that lasts a while.

[Drakkon]

well i had money to waste so got me an Asus A8N - SLI Deluxe /w a A64 3500+ proc. Now the quesstion goes what to get video wise, I gan either get dual 6600 GT's to SLI or one 6800GT or maybe an x800, would rather not get a 7800 GTX just cause frankly its too much $$$ for something new that will be beat out in a couple of weeks and drop in price fast enough anyways :P

[El Sid]

Just wanted to point out that while each card does in fact render half the screen, each of the cards' load can be adjusted. For example, if it's an outdoor scene, the upper video card should only have to render sky while the lower card renders all the tough stuff (ground, vegetation, baddies, etc.).
To even the load, some of the lower parts of the screen can be passed off to the upper video card.

Ati's Crossfire is a little different in that each video card renders opposite checker board patterns. If that's not clear enough, then imagine a checkerboard. One video card renders the "black" squares, while the other board renders the "white" squares.

3dfx used a different approach than either nVidia or Ati. Each video card rendered every other line.

[Da Lucky 1]

3dfx used a different approach than either nVidia or Ati. Each video card rendered every other line.

i heard nvidia's sli renders every other line

[El Sid]

Originally Posted by Da Lucky 1

i heard nvidia's sli renders every other line

Nope. Have a read.

Currently, SLI allows you to accelerate rendering using two effective modes, which map to around four general cases of multi-GPU rendering. The first, SFR or split-frame rendering, has each graphics card render a portion of the screen, split horizontally. One card, the primary device on the PEG host, is responsible for the top section of the screen, the secondary device therefore responsible for the bottom. That situation is then load balanced. More on that shortly.

The second mode is AFR, or alternate-frame rendering. For each graphics device in the system, the driver round-robins the graphics commands and data to each device, forcing each device to render a frame in turn. For a dual-GPU SLI setup, each device renders a frame, waits for a frame, then renders a frame, ad infinitum. Interleaved with the second device doing the same, that's AFR in a nutshell.

[Scooby]

The checkerboard pattern sounds much more effective...

[Drakkon]

Originally Posted by Scooby

The checkerboard pattern sounds much more effective...

I think your right, if you use any of the 3d rendering packages out there, they render by a checkerboard algorithm...but seems like by the time ati comes out with boards/cards for the setups nvidia will have perfected their algorithm and cards such that the preformance will be there to beat them out already. Why is ati taking so long in releasing their "version"?

[El Sid]

You know, I would be happy if Ati didn't even bother with Crossfire as long as they can finally get r520 out the door.
I like Ati, but they've really dropped the ball.

[oblivious_maximus]

They're definitely showing up late, that's for sure. However, I do believe that Crossfire is their first attempt at an entire system chipset (north and south bridges), you have to expect them to take a little time to learn the ropes. The cool thing is that (AFAIK) there's already Crossfire compatible video cards out there just waiting the motherboards to be released.

I saw a very limited article on 3 ECS crossfire motherboards the other day. It didn't include much other than pictures of a p4 model and 1 of their A64 models, and general mobo specs (chipset, expansion slots, ram types, etc). There were 2 athlon64 models in the works but there was only a picture of one of them. I just hope the system chipsets are up to snuff, otherwise people are just gonna wait for the next ones before they even consider not going nf4/SLI. I'll see if I can dig up a link to that limited preview...(edit: seems this site is no longer up-it was pcper.com /edit)



Drakkon: dunno if it's too late, I think you shouldn't consider anything less than a 6800 series card. Get a decent one(ie: GT) now and another in a couple months and you'll be good for a long while methinks.

[Drakkon]

I splurged and went with the 7800GT OC out there for $350 :P oh well this'll be the upgrade that lasts me at least a couple years maybe lol

[hans5849]

GTX GTX GTX

[oblivious_maximus]

I think a GT OC would be a way better deal (but I'm not up on american pricing) - $560 versus $730 for the GTX OC up here (plus 15% tax).

oh well this'll be the upgrade that lasts me at least a couple years maybe

It certainly has the potential to be. Pick up another GT OC in 6 months when the 8800 GT-XX!R comes out. You know you want to.

[El Sid]

They're definitely showing up late, that's for sure. However, I do believe that Crossfire is their first attempt at an entire system chipset (north and south bridges), you have to expect them to take a little time to learn the ropes.

Although I agree that Ati is trying to make sure they have things going properly before release, there is still a problem: with nVidia having released their 7800 series in full force along with working SLI, Ati doesn't have time to learn the ropes. They need to at least get r520 out the door and in consumer hands or they're going to end up like Matrox or even 3dfx in a worst case scenario.
And don't nobody scoff at me and tell me that it can't happen. It happened to the unbeatable 3dfx when everyone said it wouldn't.

[ivanolo]

I think nVidia has resolved some of the issues that were plaguing SLI since its inception. I gotta confirm this, but I believe that you don't need two cards from the same manufacturer, or with identical BIOS versions, anymore. SLI for the 6200 and 6600 is now available, and the special bridge is not required anymore, although performance will decrease without it. It's all done at the driver level. Plus, the nForce 4 SLI x16 was announced recently. That means you get 2 PCIe slots with x16 lanes! ATi's solution may prove to be better when it becomes fully available, but nVidia is working hard to establish itself out there. And, with the GeForce 7, the GeForce 6 line of cards is becoming more and more affordable....