The main point of this article was to analyze the performance of a Quad SLI system while benchmarking it against other Multi-GPU solutions from NVIDIA and ATI. All of the video cards we chose for testing offered the best performance for their class. The speed at which they rendered scenes and the image quality they offered were unbeaten by other video cards. In addition, these video cards also allowed for resolutions to be set at very high levels.

The tests that were run at a resolution of 1280x1024, the native size for most 19 inch TFT screens, shows us that that a Quad SLI system has very little chance to be fully being taken advantage of at lower resolutions. It is necessary for a configuration of this type to be used at higher resolutions with AA and AF being turned on in order to show its true potential.

The first element of the Quad SLI system that is necessary to discuss is the cost. Before actually discussing the price involved for buying two GeForce 7950 GX2 video cards, it is important to discuss the price of the display. In order to take advantage of Quad SLI, it is necessary to have a monitor that can actually support high resolutions. At the time of this article’s writing, two monitors that fully support a resolution of 2560x1600 pixels are the Dell UltraSharp 3007WFP and the Apple M9179LL/A. Both of these displays retail for $1,709.10 and $1,999.00 respectively. Combined with the cost of all 2 GeForce 7950 GX2 video cards, it is easy to see why a Quad SLI setup isn’t for the everyday user. In fact, it is for users that go a bit beyond even “hard core.”

The price you would spend on a pair of GeForce 7950 GX2 video isn’t far behind the costs for the display. Currently, a single 7950 GX2 card is retailing for around $500. For a Quad SLI setup, it would naturally be required for you to buy two 7950 GX2 cards, coming in for a total cost of around $1,000. Add this to the cost of a high end processor (you don’t want your performance to be CPU limited) in addition to the cost of a high-end power supply unit, and you can see why a budget with a lot of overhead is considered necessary to build this kind of system.

If you are considering purchasing a Quad SLI system, you might also want to put into consideration that DirectX 9 cannot fully take advantage of Quad SLI. DirectX 9, at the moment, hinders performance by not supporting queuing of enough back-buffers when working in AFR mode. This is a serious limitation to Quad SLI’s and doesn’t allow us to fully exploit it power. As can be seen in our tests, the 7950 GX2 performed the best out of all single slot solutions nearly every time when being tested against other single slot video cards. Despite this, in the section dedicated to scaling performance from one to two video cards, our results showed that with many titles Quad SLI was not able to scale performance as well as the other SLI and Crossfire configurations. It is not possible, at least at the present moment, to bypass the performance limiting problem DirectX 9 places us in. For now, we will have to wait until Microsoft releases DirectX 10 in order to fix this issue. At that time, NVIDIA’s G80 GPUs, and possibly a G80 Quad SLI solution, will most likely already be available on the market.

At this early stage of its release, Quad SLI seems to be suffering from the same limitations that plagued SLI when it first debuted. As can be expected, we are still waiting for Quad SLI drivers to mature. At the moment, driver problems often have Quad SLI performing slower than other SLI or Crossfire configurations. In time, optimizations to the drivers’ code will most likely allow us to take much more advantage of the presence of four GPUs. Also, when Quad SLI is fully compatible with more games, we should begin seeing it scale performance similar to how it did with Prey in many more situations.

Quad SLI is an excellent technological demonstration from NVIDIA. However, because the drivers are still at a very early stage and because DirectX 9’s limitations on its performance, we are not able to presently take full advantage of the theoretical performance a system with four GPUs would have. We believe that when the G80 architecture debuts, we will see Quad SLI technology undergo a large improvement. For the moment, however, in consideration to the extremely high cost of building a Quad SLI system and also because the release of the G80 is very near to us now, we see it as very difficult to actually advise you to purchase a Quad SLI system right now.

We believe that further optimizations to Quad SLI’s driver code and the release of DirectX 10 will greatly increase the performance and value of Quad SLI. Quad SLI is a technology that has a lot of potential and although it doesn’t currently offer enough performance to justify its cost, in the coming months we will most likely see many improvements be made to the technology.