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NVIDIA's Quad SLI: Demystifying the rumors February 16, 2006 |
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Summary: Without a doubt, one of the most talked about new technologies that debuted at the Consumer Electronics Show last month was NVIDIA's Quad SLI technology showcased in the Dell XPS 600 Renegade PC. In today's article we go over the technology behind it as well as answer some of the more common questions -- when will Quad SLI make its debut on the PC, and most importantly to the DIY market, when will cards hit retail? All those questions and more are answered! We've also conducted a Q&A session with Dell complete gameplay video footage of the system up and running F.E.A.R. in full 2560x1600 glory on a Dell 3007WFP monitor. Check it all out inside!
 Introduction | Page:: ( 1 / 4 ) |
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Quite a few new technologies made their debut at Consumer Electronics Show this year. In the mobile world, Intel’s Core Duo processor made a big splash, while multimedia mavens no doubt were excited to see the first crop of HD-DVD and Blu-Ray players from Sony, Toshiba, Pioneer, and many others on display.
For the PC gamer or hardware enthusiast though, the big news from the show was no doubt the Dell/NVIDIA Quad SLI announcement.
Up to now NVIDIA’s SLI technology has been limited to just two GPUs. Two GPUs running in SLI has been just fine and all for gaming at say 1280x1024 or 1600x1200 with 4xAA and 16xAF, but as any gamer with a high-end 21”+ CRT will tell you, 2048x1536 has been the holy grail of gaming for quite some time now. In addition, thanks to rapidly falling LCD prices, an increasing number of gamers are running 24” LCDs like Dell’s highly popular 2405FPW at resolutions as high as 1920x1200, and a new crop of 30” LCDs are flooding the marketplace driving resolution demands even higher. The Dell 3007WFP and Apple Cinema display both run at a native res of 2560x1600. In fact, Dell proudly proclaims that the 3007WFP boasts "over three times the resolution of so-called 'high-def gaming' that comes with an Xbox 360."
To game at resolutions this high with adequate frame rates, two graphics cards just aren’t enough. We’ve also discovered that even NVIDIA’s fastest GeForce 7800 GTX 512MB card begins to chug with NVIDIA’s 16x SLI AA mode. This is where NVIDIA’s Quad SLI technology comes in.
As its name implies, Quad SLI doubles up on the SLI goodness, combining four GPUs to provide double the performance of a conventional SLI setup. NVIDIA also includes a new 32x SLI AA mode that’s unique to Quad SLI.
How it works
Quad SLI is much more complicated than just combining four cards into one system though. In order to make Quad SLI compatible with as wide a range of PCs as possible, NVIDIA combines two GPUs onto one physical card. More specifically, each Quad SLI card combines two PCBs onto one board.
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In the case of the Dell demonstration launched at CES, the PCBs for two GeForce 7800 GTX 512MB GPUs were grafted onto one board, requiring one x16 PCI Express graphics slot. You must then combine this card with a second board to enable Quad SLI. The whole setup only requires two x16 PCI Express graphics slots, even though it looks like four cards at first glance.
| Installation | Page:: ( 2 / 4 ) |
How it works (cont’d)
The PCB used for each GPU is longer as well. This is necessary in order to house the larger cooler as well as provide room for the additional circuitry NVIDIA adds to Quad SLI cards. This added circuitry is comprised of an additional chip that is used to provide both GPUs on the Quad SLI card with 16 PCI Express lanes despite the fact that only one physical x16 PCI Express graphics slot is used. How does it do this you ask?
It turns out that the chip acts as a PCI Express “splitter” of sorts. From one x16 PCI Express graphics slot, the chip splits it into two x16 connections, enough for one full x16 connection per GPU on the card. The chip is also responsible for merging the data back from both GPUs into one x16 connection.
Compatibility
We’ve been told that NVIDIA’s Quad SLI solution is only compatible with their nForce4 SLI X16 chipsets. Older nForce4 SLI chipsets aren’t compatible with Quad SLI.
In addition, just to clarify some of the confusion, while the Quad SLI platform at CES was demonstrated on an nForce4 SLI X16 Intel Edition motherboard, NVIDIA’s Quad SLI card solution won’t be unique to Intel – both X16 nForce4 SLI chipsets are supported. In fact, considering AMD’s high adoption rate among gamers, NVIDIA expects Quad SLI to be just as popular on the AMD platform as Intel.
It’s important to note however that pseudo-Quad SLI can’t be rigged to run on motherboards with four PCI Express graphics slots by using four different graphics cards.
If you recall, late last year Gigabyte announced an nForce4 SLI X16 Intel Edition motherboard with four PCI Express graphics slots, the GA-8N-SLI Quad Royal. While the board uses NVIDIA’s nForce4 SLI X16 Intel Edition chipset, only two of the board’s four PCI Express graphics slots provide full 16-lane PCI Express capability. Gigabyte hasn’t been specific on how many lanes the secondary graphics slots are capable of supporting, but since the South Bridge that the PCI-E slots are tied to is capped to 20 lanes total, our guess is that you’re limited to just one lane per slot, with the remaining two lanes going to the secondary x1 PCI Express slots on the motherboard (16 lanes for one graphics slot + 2 lanes for the third and fourth graphics slot + 2 lanes for the x1 expansion slots for a total of twenty).
In other words, while two NVIDIA Quad SLI cards should work on the Gigabyte GA-8N-SLI Quad Royal (provided the two Quad SLI cards are running in the board’s two x16 PCI-E slots), running four GeForce 7800 GTX 512MB boards on the Quad Royal for pseudo-Quad-SLI won’t work.
Likewise, you also can’t combine two GeForce cards with dual GPUs on one card together for Quad SLI. As you probably know by now, both ASUS, Gigabyte, and MSI have all developed GeForce 6800 GT and GeForce 7800 GT cards that combine dual GPUs onto one PCB for single-card SLI. NVIDA’s Quad SLI announcement won’t allow you to combine two of these boards together for pseudo-Quad SLI.
| The future | Page:: ( 3 / 4 ) |
We’d guess that NVIDIA likely chose to demonstrate Quad SLI with Dell because NVIDIA knew in advance that Dell was going to launch their 3007WFP LCD at CES. Think of it from NVIDIA’s perspective – what better way to showcase Quad SLI than to show it up and running on a 30” LCD at 2560x1600?
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Also, while this wasn’t made clear on launch day at CES, NVIDIA was quick to reiterate to us that this wasn’t a new product introduction. Instead NVIDIA characterized the Quad SLI announcement as a technology demonstration.
Basically, don’t expect NVIDIA to start selling Quad SLI GeForce 7800 GTX 512MB-based cards tomorrow. In fact it’s most likely that a GeForce 7800 GTX-based Quad SLI card will never see retail shelves. Instead you should expect the first Quad SLI cards to ship with upcoming GeForce GPUs that haven’t been announced yet. After all it wouldn’t make much sense to fork over thousands of dollars for a GeForce 7800 GTX-based Quad SLI solution if a newer GPU were available in just a few months (or less) would it?
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Based on all this, we seriously doubt that the XPS 600 Renegade as it was demonstrated by Dell at CES last month will ever see the light of day. On the contrary, the final Quad SLI solution should be even faster!
| Availability/Conclusion | Page:: ( 4 / 4 ) |
This could be a repeat of the exact same situation that occurred with the GeForce 7800 GTX 512MB late last year, where a limited number of cards could be found on store shelves on launch day before supplies dried up. Since then, we’ve discovered that a large reason why NVIDIA’s had so many nagging retail availability issues with this GPU in particular is because OEMs were just eating them up for use in their flagship PCs. These systems sell for the highest profit margins for manufacturers and bring in lots of buzz due to their extraordinary performance, so the GeForce 7800 GTX 512MB has been in high demand since its introduction.
We’re hoping our sources will be wrong on this point, and that NVIDIA’s board partners will be able to supply the retail and OEM markets with Quad SLI cards equally well, but we’ll just have to wait and see how it all plays out.
In terms of when you can expect the first Quad SLI cards to ship, as the old saying goes, we could tell you, but then we’d have to kill you. All indications are that it won’t be long though. At CES Dell stated they’d begin shipping Quad SLI in the March/April timeframe.
Closing thoughts
Just when you thought two graphics cards was overkill, NVIDIA ups the ante by introducing Quad SLI. The best part about their technology is that NVIDIA doesn’t require anything special to get it up and running – existing nForce4 SLI X16 motherboards should work fine with no problems. Unlike ATI’s CrossFire, no dongles are required while NVIDIA’s ForceWare driver features SLI profiles that can be customized for specific games.
But just how much will a Quad SLI setup set you back? That’s the question that still hasn’t received a specific answer just yet. We’ve got a feeling though that Quad SLI is going to be one of those products that if you have to ask, chances are you can’t afford it. We just hope that those DIY’ers who can afford Quad SLI when it debuts will be able to purchase it without having to buy a complete system. Only time will tell on that particular subject though…
For more on Quad SLI and Dell’s XPS 600 Renegade system, check out our video footage from CES, including gameplay footage of F.E.A.R. running at 2560x1600 on the Dell 3007WFP!