Introduction

In our GeForce 7600 GS Comparison article, we explained the importance of the value and mainstream segments of the 3D market to NVIDIA. To make a long story short, these more affordable cards are vitally important to improving NVIDIA’s market share. After all, the vast majority of consumers in the PC market won’t spend $500 or more on the latest and greatest graphics card.

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!

GeForce 7950 GX2 (top), 7900 GX2 (middle), X1900 XTX (bottom)

Alienware ALX Quad SLI system

Water-cooled GeForce 7900 GX2 cards

Inside the Alienware system

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…