Little more than two years have passed since NVDIA first introduced their SLI technology. Short for Scalable Link Interface, SLI is the first solution to be able to connect two PCI-Express video cards based on the same GPU in a way that they will operate parallel to each other. This type of approach allows, at least on paper, to have an increase in performance of up to double what you would normally have with a single video card. In the first months of SLI’s release, it potential was limited by driver problems and other software errors.

However, forwarding two years into the future and with the release of several new driver versions from NVIDIA, SLI technology has really matured as a whole. Stability has been greatly improved and support has been added to an increasing list of games. SLI support has also been made more accessible to the general public with the release of average and entry level video cards that support the technology. Currently, SLI will even be made available on NVIDIA’s most budget level class of GeForce 7 video cards, the 7100 GS, thus making it a solution that is affordable and available to a vast amount of computer users.

At this moment, SLI and Crossfire technologies can be considered the first full phase of maturity for a broader category: multiple GPUs. The next phase is for more than two video cards being linked up to each other in an effort to, yet again, increase performance. As NVIDIA was first to reach the market with a dual video card solution, they have yet again been able to beat ATI in announcing a solution that utilizes more than two GPUs. The technology is, none other than, Quad SLI (the name isn’t very original). Quad SLI has four GPUs operating parallel to each other, theoretically doubling the performance in respect to an SLI setup.

Quad SLI on display by NVIDIA at CES 2006 in Las Vegas

The first public demonstration of this technology from NVIDIA happened January 2006 at the Consumers Electronics Show (CES) of Las Vegas. From that moment on, NVIDIA displayed many more glimpses of Quad SLI at various events, however, its performance at that time was not an accurate example of its true potential due to early driver problems. Initially, Quad SLI was going to be available only in systems of partner OEMs, and NVIDIA, in fact, allowed the technology to be used, exclusively at first, in Dell’s XP 600 Renegade. The XPS Renegade was made available for purchase in March 2006 at the price of $10,000. The system came locked and loaded with a pair of custom NVIDIA 7900GTX 512 MB cards. As can be expected, the systems were extremely limited and available to a very small portion of the public because of their price. Although the XPS Renegade looked cool, we personally preferred going for a solution that wouldn’t have required us to sell our car.

The 7950 GX2 was released for retail June 5, 2006. The 7950 GX2 replaced its predecessor the 7900 GX2, which suffered from many problems including layout, size, noise, power consumption, and price. With the release of the 7950 GX2, much of these problems have been addressed and changed. The PCB has been taken down to the size of a regular 7900 GTX and now only a single PCIe power connector is required. Although the GeForce 7950 GTX was compatible with Quad SLI on release, users could not take advantage of this feature until the release of the Forceware 91.45 drivers. With the release of the new drivers, this technology has been made officially available to customers who are passionate enough to want to assemble a Quad SLI system alone.

Quad SLI, as we will see in the course of this article, is a technology that traces its roots back to SLI. At the moment, driver compatibility and DirectX 9 are the main limiting factors in addition to cost and availability.

sistema Quad SLI con schede GeForce 7950 GX2

In the course of this analysis we will benchmark our Quad SLI setup that utilizes two 7950 GX2 (four GPUs) video cards against a system armed with two GeForce 7900 GTs running in SLI, a system with two ATI Radeon X1900XTX video cards running in Crossfire and one system with an ATI Radeon X1950XTX video card also running in Crossfire.