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GeForce 7900 GX2/7950 GX2 Quad SLI Performance Update July 27, 2006 Brandon Sandman Bell |
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Summary: With Alienware's top-of-the-line GeForce 7900 GX2 Quad SLI-powered ALX Quad SLI system in hand, and a pair of GeForce 7950 GX2s, we figured it was time to take another look at the performance of NVIDIA's Quad SLI platform. Fortunately we can report that a lot of the issues that we ran into a few months ago have now been resolved. So how do the Quad SLI cards compare to the GeForce 7900 GTX SLI and Radeon X1900 XTX CrossFire? Find out in today's article!
 Introduction | Page:: ( 1 / 12 ) |
On the opposite end of the spectrum are NVIDIA’s halo products. These are the graphics cards that showcase all the strengths of NVIDIA’s latest technologies, many of which can be found in their lower priced products. These high-end parts are the ones that make all the headlines and draw all the buzz. Basically, they’re responsible for getting consumers excited about the brand: there may not be as long a line of people looking to purchase these flagship graphics cards, but they’re the ones that get people in line in the first place. Because of this, these more expensive products play an important role for NVIDIA as well.
We witnessed this most dramatically at the Consumer Electronics Show earlier this year. NVIDIA’s Quad SLI technology was arguably the most talked about hardware debut at the show, trumping Intel’s Core Duo CPU introduction and snagging CNET’s “Best of CES” award before the final product was even ready for public consumption. That’s precisely the kind of buzz you can generate with the right high-end product.
NVIDIA isn’t the only one that reaps the benefits when this occurs, their partners do too. Case in point would be the Alienware ALX Quad SLI system that sat on the frontpage of Alienware’s website for some time; quite a few of you guys asked us if we’d take a look at this system in particular, and you guys are enthusiasts who typically build your own rigs – imagine the lust on the part of the public (and previous Alienware owners) when they saw the ALX system!
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Now that NVIDIA and Alienware have had a bit more time to work some of the bugs out of Quad SLI, a fully-equipped Alienware ALX Quad SLI system sits on our desk for testing. As a result, we figured this would be a good time to take another look at the platform.
A note on performance
With four GeForce 7900 GPUs running in tandem, NVIDIA’s Quad SLI packs quite a bit of punch. However, in order to truly realize the full potential of a Quad SLI system, you’re going to need a very high-end monitor capable of running mega resolutions like 2048x1536 or even better, 2560x1600. For those of you with a 20” LCD who are stuck at 1600x1200 or 1680x1050, Quad SLI probably isn’t for you if you plan on gaming at 4xAA/16xAF. We’ll show you the benchmarks as proof a little later.
According to NVIDIA, this is due in part to the limitations of DirectX 9, NVIDIA’s Nick Stam tells us: “The fact that DX9 limits the number of back buffers that can be queued, it doesn't allow 4-way AFR, so we fall back to AFR of SFR in some cases or 2-way SLI in others with D3D apps.” Basically what he’s saying is that NVIDIA’s preferred SLI technique, alternate frame rendering (AFR), doesn’t scale well with Quad SLI in all cases when running Direct3D apps. Apparently due to limitations in DX9, NVIDIA’s not able to queue up enough frames to drive the four GPUs in a Quad SLI setup with high performance, so instead of running 4-way AFR mode, they have to fallback to slower modes, such as AFR of SFR, or 2-way SLI as Nick mentions above.
Fortunately 4-way AFR works better in OpenGL apps, and this problem has been resolved in DirectX 10.
Complicating matters are the clock speeds of Quad SLI cards. Since Quad SLI boards run at slower clocks than a GeForce 7900 GTX, (500MHz GPU/600MHz memory versus 650MHz GPU/800MHz memory on a 7900 GTX) this means that there are cases where a Quad SLI setup may be no faster than a 7900 GTX SLI rig, in fact it may actually run closer to the performance of a pair of 7900 GTs running in SLI, which is a little slower.
As you can imagine, it’s important to have the fastest CPU possible to drive Quad SLI as well. After all, you wouldn’t want to drop $1,100 on a pair of GX2 graphics cards only to be held up by your CPU.
When you do have Quad SLI up and running properly though, it’s a sight to behold, especially at 2560x1600 on a 30” monitor. This is where Quad SLI really shines…
| Image quality | Page:: ( 2 / 12 ) |
NVIDIA supports three SLI anti-aliasing modes for Quad SLI: the traditional 8x and 16x modes that are provided by all SLI-capable cards, and a special 32xAA mode that’s unique to Quad SLI. With a Quad SLI graphics setup providing up to 96 pixel shaders and over 150GB/sec of peak memory bandwidth on tap, the premise is that you can not only have the sharpest image quality available on the PC thanks to these SLI-AA modes, but you’ve got enough pixel-pushing horsepower to run that eye candy with the highest frame rates available on the PC as well. Let’s take a look at some screenshots so you can see how much better SLI-AA looks over the more traditional 4xAA setting:
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When looking at the above screenshot, the most obvious area to see the difference between 4xAA and 8xSLI-AA is the large tree in the scene above: (note that this is a static tree, i.e. the branches don’t sway in the wind, which could affect direct comparisons of the screenshots)
GeForce 7900 GX2 4xAA
GeForce 7900 GX2 8xSLIAA
Take a look at the very top of the tree. 8xAA does a slightly better job of clearing up the jaggies on the top branches, particularly the top branch on the left. The foliage in the tree looks sharper under 8xAA as well. You’re going to want to download these screenshots and compare directly to see that though.
Another area where you can spot some differences is just to the right of the tree, along the edge of the building just behind it:
GeForce 7900 GX2 4xAA
GeForce 7900 GX2 8xSLIAA
Here the difference is a little more subtle, but the top edge of the building is ever so slightly sharper with 8xSLI-AA. Honestly though it’s a little easier to eyeball the differences up and running inside the game rather than looking at static screenshots.
4xAA vs 8xSLI-AA Performance
Remember how we mentioned on the previous page that Quad SLI isn’t ideal if you only plan on running 4xAA/16xAF? Now we’ll show you benchmarks as proof. On the next few pages we’ll compare the Alienware ALX Quad SLI rig (which runs with a pair of GeForce 7900 GX2 cards) with similarly-equipped GeForce 7900 GTX SLI and Radeon X1900 XTX CrossFire setups.
First let’s look at the system’s we’re testing…
| Test Systems | Page:: ( 3 / 12 ) |
System Setup
AMD Athlon 64 FX-62
ASUS M2N32-SLI Deluxe
2GB Corsair TWIN2X2048-6400C4
ATI Radeon X1900 XTX/Radeon X1900 CrossFire
Catalyst 6.6
GeForce 7900 GTX SLI
Driver version ForceWare 91.31
BFG GeForce 7950 GX2 Quad
1x BFG GeForce 7950 GX2
Driver version ForceWare 91.37
Alienware Aurora ALX Quad SLI System
2xGeForce 7900 GX2
Driver version ForceWare 87.25
Western Digital Raptor 75GB
Windows XP Professional SP2
DirectX 9.0c
Benchmarks
Half-Life 2 Lost Coast
Far Cry 1.33 (1.4 patch for ATI cards)
F.E.A.R. 1.05
Quake 4 1.2
Elder Scrolls IV: Oblivion
Battlefield 2 1.3
Notes
We’re combining quite a mixture of configurations this time around, due in large part to the variation in ForceWare drivers. NVIDIA’s latest driver for the GeForce 7900 GX2 is ForceWare 87.25, so we’re forced to test with a slightly older driver, but those are the breaks. We then used ForceWare 91.37 for the GeForce 7950 GX2 cards, as that’s the only available driver at the moment that enables Quad support for the 7950. Finally, the 7900 GTX setup is tested with ForceWare 91.31, NVIDIA’s latest WHQL driver. The Alienware ALX system is running with a Foxconn nForce 590-SLI motherboard, 2GB CAS4 RAM, and an FX-62 CPU by the way.
Also keep in mind that the 4xAA GeForce 7950 GX2 numbers are with a single card, whereas the 8xSLI-AA numbers are taken with a pair of GeForce 7950 GX2 boards running Quad SLI.
| 1600x1200 4xAA/16xAF results | Page:: ( 4 / 12 ) |
Quake 4 – OpenGL
Battlefield 2 – Direct3D
Oblivion – Direct3D
Half-Life 2 Lost Coast – Direct3D
Far Cry – Direct3D
F.E.A.R. – Direct3D
| F.E.A.R. Performance 1600x1200 | ||
| Card | Min FPS | Max FPS |
| GeForce 7900 GX2 Quad | 49 | 270 |
| GeForce 7900 GTX SLI | 47 | 222 |
| Radeon X1900 XTX CrossFire | 30 | 222 |
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Notes
At 16x12, F.E.A.R. is the only title that takes advantage of our Quad setup. As you can see, everywhere else the GeForce 7900 GX2 Quad is outgunned by GeForce 7900 GTX SLI and Radeon X1900 XTX CrossFire (with the exception of Quake 4), in fact the 7900 GX2 Quad barely outpaces the single GeForce 7950 GX2: in fact performance is tied in Quake 4 and Half-Life 2: Lost Coast. Driver overhead may be playing a bit of a role here, but it’s surprising to see nevertheless. We weren’t able to complete our tests with the CrossFire rig in Far Cry at 1600x1200 for some reason.
| 2560x1600 4xAA/16xAF results | Page:: ( 5 / 12 ) |
Quake 4 – OpenGL
Battlefield 2 – Direct3D
Oblivion – Direct3D
| Oblivion Performance 2560x1600x32 | ||
| Card | Min FPS | Max FPS |
| GeForce 7900 GX2 Quad | 22 | 39 |
| GeForce 7900 GTX SLI | 29 | 51 |
| 1xGeForce 7950 GX2 | 20 | 40 |
| Radeon X1900 XTX CrossFire | 37 | 58 |
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| Oblivion Foliage Performance 2560x1600x32 | ||
| Card | Min FPS | Max FPS |
| GeForce 7900 GX2 Quad | 13 | 19 |
| GeForce 7900 GTX SLI | 17 | 25 |
| 1xGeForce 7950 GX2 | 12 | 19 |
| Radeon X1900 XTX CrossFire | 26 | 33 |
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Half-Life 2 Lost Coast – Direct3D
Far Cry – Direct3D
F.E.A.R. – Direct3D
| F.E.A.R. Performance 2560x1600 | ||
| Card | Min FPS | Max FPS |
| GeForce 7900 GX2 Quad | 26 | 186 |
| GeForce 7900 GTX SLI | 23 | 154 |
| 1xGeForce 7950 GX2 | 21 | 133 |
| Radeon X1900 XTX CrossFire | 25 | 150 |
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Notes
Under the greater demands of 2560x1600, the situation improves a little for Quad SLI, Quake 4 is now showing an advantage of nearly 30% over GeForce 7900 GTX SLI, while the Quad card outruns 7900 GTX SLI by 14% in F.E.A.R.
All isn’t rosy for GeForce 7900 GX2 Quad however, as everywhere else the SLI and CrossFire rigs are still delivering better performance. Again, part of this is due to the Quad cards lower clocks, and extra driver overhead may be playing a role. It also looks like the Quad card may be falling back to 2-way SLI in some tests.
In order to really see where a Quad SLI rig shines, you’ve got to turn the settings up a little higher. Let’s crank the AA up to 8x!
| SLI8xAA HL2 Lost Coast | Page:: ( 6 / 12 ) |
Half-Life 2: Lost Coast – Direct3D
| SLI8xAA Quake 4 | Page:: ( 7 / 12 ) |
Quake 4 – OpenGL
| SLI8xAA F.E.A.R. | Page:: ( 8 / 12 ) |
F.E.A.R. – Direct3D
| F.E.A.R. Performance 2048x1536 | ||
| Card | Min FPS | Max FPS |
| GeForce 7900 GX2 Quad | 26 | 156 |
| GeForce 7900 GTX SLI | 19 | 113 |
| GeForce 7950 GX2 Quad | 25 | 163 |
| Radeon X1900 XTX CrossFire | 16 | 110 |
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| SLI8xAA Oblivion Mountains Bloom | Page:: ( 9 / 12 ) |
Oblivion – Direct3D
| Oblivion Performance 2048x1536x32 | ||
| Card | Min FPS | Max FPS |
| GeForce 7900 GX2 Quad | 34 | 63 |
| GeForce 7900 GTX SLI | 23 | 44 |
| GeForce 7950 GX2 Quad | 33 | 63 |
| Radeon X1900 XTX CrossFire | 19 | 39 |
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| SLI8xAA Oblivion Foliage Bloom | Page:: ( 10 / 12 ) |
Oblivion – Direct3D
| Oblivion Performance 2048x1536x32 | ||
| Card | Min FPS | Max FPS |
| GeForce 7900 GX2 Quad | 24 | 28 |
| GeForce 7900 GTX SLI | 16 | 19 |
| GeForce 7950 GX2 Quad | 24 | 29 |
| Radeon X1900 XTX CrossFire | 18 | 21 |
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| SLI8xAA Battlefield 2 | Page:: ( 11 / 12 ) |
Battlefield 2 – Direct3D
| Conclusion | Page:: ( 12 / 12 ) |
In Quake 4, our GeForce 7900 GX2 setup was up to 33% faster than the GeForce 7900 GTX SLI rig at 2560x1600. That’s a performance improvement of 1.5x. Even at 1600x1200 with 8xSLI AA we witnessed a 26% gap between the GeForce 7900 GX2 Quad SLI and the GeForce 7900 GTX SLI setup. Quad SLI’s performance in F.E.A.R. was equally impressive: at 1600x1200 the Quad SLI setup ran 29% faster than the GeForce 7900 GTX SLI rig did, and by 2048x1536 the gap increased to 31%. Half-Life 2 Lost Coast didn’t quite show the same margins, but by 2560x1600 the Quad SLI setup turned in scores that were 28% faster than the GeForce 7900 GTX SLI. Finally we saw gains of up to 25% in Battlefield 2, while the Quad SLI rig was nearly 30% faster than GeForce 7900 GTX SLI in Oblivion.
The performance picture is reversed with just 4xAA – even at 2560x1600 with 4xAA/16xAF the GeForce 7900 GTX SLI rig is capable of outperforming Quad SLI in many cases. Again, anyone planning to run a Quad SLI setup at 4xAA is just wasting their money.
On the software side, NVIDIA’s latest ForceWare driver has come a long way since we first took a look at Quad SLI in May. Both ForceWare Quad SLI drivers were much more stable, although we’ve got to give the nod to the GeForce 7950 GX2’s ForceWare 91.37 drivers; we didn’t encounter a single lockup or crash with 91.37, and that’s definitely a good thing.
We also have to give NVIDIA major kudos for their work over at slizone.com, listing all the compatible motherboards (and BIOS revisions), power supplies, etc, in fact we believe NVIDIA may be playing it a bit too conservative with their power supply recommendations, we ran all our tests on an OCZ 600W power supply without any problems, although obviously if you’re running a system with multiple drives that will bump up the power requirements.
In closing, we’re encouraged by the progress NVIDIA has made with Quad SLI. With GeForce 7950 GX2 cards selling for a little over $100 more than your typical GeForce 7900 GTX, you can actually make an argument that the GeForce 7950 GX2 is a better value. Sure, you can pick up two GeForce 7900 GT cards and run them in SLI for less money, but the beauty of Quad is that you can buy one card today and get performance similar to the 7900 GT SLI setup, and a second card six months from now. By then GeForce 7950 GX2 cards should be selling for significantly less than they are today, and you’ll be running Quad SLI.
Of course, the biggest argument against spending $500+ on a new graphics card right now is DirectX 10. If you can afford to wait, it certainly wouldn’t be a bad idea. But if you were on the fence about Quad SLI because of the initial performance reports, don’t be. As long as you’re aware of Quad SLI’s limitations and exploit the power of GeForce 7900 GX2/GeForce 7950 GX2 appropriately, Quad SLI gaming can be a very rewarding experience.