Board analysis

Top view of the 7900 GX2 Quad SLI cards

A closer shot of the board

What’s in a name?

One of the more confusing aspects of Quad SLI is the actual name of the product. Over the past few months we’ve seen it referred to by multiple product names, ranging from “GeForce 7900 Duo” to the “GeForce 7900 GX2” and “GeForce 7900 Quad”. Judging by the EVGA graphics cards used in our ABS Quad SLI system, it looks like NVIDIA’s board partners are equally confused, as the back of both cards was clearly labeled “e-GeForce 7900GTX QUAD”.

This label suggests that NVIDIA’s Quad SLI cards are based on NVIDIA’s recently released GeForce 7900 GTX GPU, but actually NVIDIA’s first Quad SLI card is more of a hybrid of the GeForce 7900 GT and GeForce 7900 GTX: while NVIDIA’s Quad SLI boards ship with 24 pixel shaders, 8 vertex shaders, and 16 ROPs just like a GeForce 7900 GT or 7900 GTX, NVIDIA clocks their Quad SLI boards at 500MHz on the graphics core while the memory runs at 605MHz. That’s about 50MHz faster than a GeForce 7900 GT on the graphics core, but 55MHz slower on the memory than the 7900 GT. This means a single Quad SLI card should run somewhere between a GeForce 7900 GTX SLI and GeForce 7900 GT SLI setup in terms of performance. NVIDIA says that they selected these clocks in order to “enable maximum performance within the power and thermal envelope that we are allocating.” In other words, if they cranked up the clock speeds any higher, the additional power requirements and higher thermals required would have been too high for what they were targeting.

Because of this, NVIDIA ultimately settled on the name GeForce 7900 GX2 for their Quad SLI cards.

The 7900 GTX looks tiny in comparison to the 7900 GX2

One long PCB

Physically, the GeForce 7900 GX2 looks like no other graphics card on the market. The card features an extremely long PCB that’s just over 1 foot in length, making it the longest graphics card we’ve seen in recent memory. At first glance, one GeForce 7900 GX2 card looks like two distinct graphics cards, as NVIDIA literally uses two separate PCBs on one card – each PCB complete with one GPU and its associated memory, as well as the corresponding heatsink/fan unit – but it’s actually one graphics card. If you look closely you’ll see that only the PCB on the bottom has a PCI Express interface; the two PCBs are attached together with six screws.

Both cards are pretty close in height

Mmm...Quad SLI

The heatsink/fan unit on each GeForce 7900 GX2 is a single-slot unit, somewhat similar in design to the cooler used for the GeForce 7800 GTX 256MB but elongated for better performance. An aluminum heatpipe/heatsink combination is used to draw heat off the GPU and its memory modules while a small fan is used to keep everything cool. It’s important to note that while the backplate on the GeForce 7900 GX2 has vented holes on it, suggesting that hot air exhausts out the back of the system’s chassis, this actually isn’t the case, the vents on the back of the GeForce 7900 GX2 are merely decorative, hot air from the card’s cooler doesn’t exit here. The ducted enclosure NVIDIA has employed simply isn’t long enough for hot air to escape through.