Nvidia 9800 GX2 Quad SLI

We ended our preview of Nvidia's new 9800 GX2 video card with a little teaser about an upcoming article comparing 9800 GX2 Quad SLI setup against a PSU knee shattering 8800 GTX Tri SLI configuration. In this article we will offer a small Quad SLI setup guide, take a gander at some new software available with the configuration and, most importantly, check out the performance gained with this new offering by Nvidia. Join Rage3D as we put on our protective gear, call in a warning to our local power company, and see what these babies can do!

Operating System Considerations

The concept of Quad SLI was first introduced with Nvidia's Geforce 7950 GX2. The design was undermined in many games by scaling issues due to a Windows XP issue imposing a three frame store limit. Windows Vista, however, does not have this problem, and Nvidia has worked closely with Microsoft to ensure that Windows Vista provides the best multi GPU experience, and recommends users download Service Pack 1 for Windows Vista.

Power Supply requirements

In our 9800 GX2 Performance Preview, we detailed the performance requirements of a single 9800 GX2, mentioning that an 850W PSU is recommended for Quad SLI. We recommend reviewing those requirements as well as taking a look at Nvidia's list of Compatible Power Supplies for more information. In summary, however, these are the PSU requirements for official Quad SLI support:

• PSU must pass all requirements for a single 9800 GX2 for backwards compatibility.
• PSU must have two 8 pin capable power connectors and 2 6 pin connectors. The 8 pin power connectors are a requirement for the 9800 GX2 cards to run.
• Have a total peak power of 880Watts.
• Hybrid Power support.

Test Setup

Vista Ultimate x64 SP1
Intel Core2Duo e6300 @ 3.2 GHz
XFX Nforce 790I Ultra @ 1828 FSB
2 Gigs Crucial Ballistic @ 2000 MHz
Geforce 9800GX2 Quad SLI
PC Power and Cooling 1.2 Kilowatt PSU
Olevia 27 Inch Widescreen HDTV
Forceware 174.53

Tested Configurations

9800 GX2
9800 GX2 Quad SLI
8800 GTX
8800 GTX SLI
8800 GTX Tri SLI
8800 GT SLI

2006 AFR to SFR

Due the restriction in place by Windows XP, previous Quad setups were forced to render AFR and SFR separately, with AFR on two GPUS and SFR on the other two GPUS. While this method was effective for games requiring only one or two rendering passes for simple tasks like multi-texturing, it is not uncommon to see 6 to 8 rendering passes occur on a single scene for things like HDR and other modern rendering techniques in modern games, effectively nullifying SFR's scaling abilities. As a result, users often saw that the Quad under Windows XP was incapable of scaling beyond dual GPU performance in worse case scenarios.

2006 AFR to SFR

Nway AFR 2008

Nvidia introduced Nway with 3 way SLI, with results showed similar scaling between 2 way and 3 way SLI. CPU bottlenecks aside, Nway 4 way SLI should scale well too since it shares the same pattern and simply builds off what Tri SLI started.

4 way SLI allows for 4 GPUs to be used in AFR mode, and Nway is fully backwards compatible with 2 way and 3 way AFR. As such, you wont need separate profiles to enable it: if it works in 2 way or 3 way it should also work in 4 way. With few exceptions, this will allow for a single driver for all SLI solutions. 4 Way AFR will not suffer from the many limitations that existed under Windows XP and should provide far more optimal scaling. Due to this Windows XP limitation, Quad SLI is only supported under Windows Vista platform.

Nway AFR 2008

Nway in Application

Talk is one thing, but lets see the performance differences by testing the new Nway 4way AFR verses AFR-SFR in Bioshock and Crysis.

Performance Thoughts: The results are conclusive, with Bioshock receiving no scaling with AFR-SFR. Likewise, the Crysis results are a disaster, with its complex rendering engine causing major performance loss when enabling AFR-SFR. Nway AFR, however, scales perfectly under both titles, offering a very good example of the dramatic changes Nway brings to performance scaling under Windows Vista.

Oblivion Performance

Performance Thoughts: As in the 9800 GX2 preview, Oblivion becomes CPU bound with 16xCSAA enabled. With 16xQ, many of the solutions become GPU bound again. In this case, the 9800 GX2 Quad SLI solution pulls ahead of the 8800 GTX Tri SLI solution, but starts hitting the same CPU barrier that effects the other systems with 16xCSAA enabled. All configurations tested are more than capable of playing Oblivion at high settings with 16xAA enabled.

Oblivion 1920x1080 16xaa

Bioshock Performance

Performance Thoughts: While a single 9800 GX2 holds up very well against an 8800 GTX SLI configuration, the Quad SLI configuration completely thrashes every other config in this test suite. Quad SLI pulls far ahead of the 8800 GTX Tri SLI Configuration in both 16xQ and 16xAA.

Serious Sam 2 Performance

Performance Thoughts: As seen in previous tests, 16xCSAA mode tends to end up in a CPU bottleneck. 16xQ once again shifts a pure GPU bottleneck back onto the hardware. In this case, 9800 GX2 Quad SLI comes up very slightly behind Tri 8800 GTX SLI, an event that may very well be memory related. Regardless, both solutions are very capable of providing stellar frame rates.

Unreal Tournament 3 Performance

Performance Thoughts: With Unreal Tournament 3, we implemented several configuration changes from the prior tests in order to make the testing more GPU limited. We used the most GPU limited map available and disabled the frame smoothing option in the .ini folder. The results were rather surprising, with most configuration able to stay above the 30 FPS mark but none able to hit the magical 60 FPS mark. The 9800 GX2 Quad SLI configuration performed the best with the 8800 GTX Tri SLI following behind by a fairly large margin. Only truly high end systems will be able to play at these settings with 16xAA enabled.  Do note that the results are different from those obtained in our previous tests since we retested all the configurations using the new test settings.

Crysis Performance

Performance Thoughts: Every Crysis player on the planet has been waiting for a configuration that can play this game at max settings and maintain enjoyable experience. Can the 9800 GX2 Quad SLI do that at this resolution? The answer is no. However by making a few sacrifices such as changing shadow volumes to medium and keeping everything at high, the game did remain playable with 4xAA/16xAF @ 1920x1080. The 9800 GX2 Quad SLI system was the only system able to provide a stable gaming experience at these settings. With the current hardware available on the market I found this to be an impressive feat.

Notes: Enabling Shadow Volumes to High causes the 9800 GX2 and 8800 GT SLI solutions to drop down to 5 FPS due to memory limitation. The 8800 GTX SLI fell to 15 FPS and the 8800GTX SLI system was able to pull out 22 FPS. Under these circumstance, the 8800 GTX's extra 256MB of memory gave it an advantage. Even with this advantage, however, the results remained largely unplayable and the mouse lag was intolerable.

nVidia 9800 GX2 Quad SLI

8800GTX Tri SLI verses 9800GX2 Quad SLI

The 9800 GX2 Quad SLI configuration held the advantage in most situations, and in those situations the advantage was considerable. There were certain scenarios where 8800 GTX Tri SLI was able to outperform the 9800 GX2 Quad configuration, the most notable being Crysis with shadow volumes at high. However the victory loses meaning when the results were unplayable. There were also some situations where the 9800 GX2 Quad SLI and 8800 GTX Tri SLI washed for performance such as Oblivion and Serious Sam 2. However both systems were able provide a solid gaming experience.

9800 GX2 Pros

• Consistently higher or equal performance than 8800 GTX Tri SLI
• Significantly less heat and thermal management than 8800 GTX Tri SLI
• Wider range of chipset support. 8800 GTX tri SLI requires a TRI SLI capable motherboard
• Lower Power requirements. The 8800 GTX Tri SLI requires a 1.1KW PSU vs. the 9800 GX2 Quad SLI configuration requirement of under 900W.
• Advanced PureVideo Tech for a better HD video experience.

8800GTX Tri SLI Pros

• An Additional 256 megs of available framebuffer, which in some scenarios can provide a benefit.
• Only requires 6 pin power connectors.

Conclusion

With the advancements to Nway and AFR scaling under Vista, the Geforce 9800 GX2 Quad SLI system is a force to be reckoned with and is able to provide the most consistent performance and gaming experience yet encountered. Quad SLI scaling is no longer hit and miss like it was back in the days of the 7950 GX2 and, unlike Tri SLI, thermal management shouldn't be as much of a concern using this setup. With SLI compatibility with any Nforce SLI capable board on the market, many more users will have the option to experience 9800 GX2 Quad SLI performance. With Nway providing a more consistent scaling experience, the 9800 GX2 is able to stand on its own and as an SLI solution.

9800 GX2 Quad SLI remains an expensive solution, the most expensive currently available. But with that expense comes the ability to use your High Definition displays at playable performance and immediate results in most applications. And those finding themselves CPU limited can enable the hidden Quad SLIAA routines in the drivers from the 7950 GX2 days that to provide a completely different experience.