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GeForce 7900 GX2: Cooling System

The design of the cooling system of the GeForce 7900 GX2 is necessitated by the design of the graphics card itself. The card consists of two PCBs placed one above another, so Nvidia had to use thin, single-slot coolers. Theoretically, the developer might have put a larger cooler at least on the top PCB, but this would make it impossible to install two GeForce 7900 GX2 into one system with closely placed PCI Express x16 slots.

The coolers are a variation of the reference cooler of the GeForce 7800 GTX which we described in our review.

There’s a U-shaped heat pipe on the cooler’s sole that directly contacts the GPU die surface. The two heatsink sections are made of thin aluminum plates. The whole arrangement is covered with a plastic cap that doesn’t let the air stream leave the heatsink.

Airflow is created by a small blower that differs from the one used on the GeForce 7800 GTX only in the color of the blades. Here, it is made of a translucent acid-green UV-reactive plastic. The fans use a 4-wire connection which implies an intelligent fan speed control system. It doesn’t guarantee quiet operation, though.

As we noted above, the cooler on the bottom PCB of the GeForce 7900 GX2 takes its air not from the thin slit between the fan’s blades and the top PCB, but through the special holes in the PCB. This doesn’t help much in a system with two GeForce 7900 GX2: only the bottom card’s top cooler and the top card’s bottom cooler are going to get enough of air for cooling. So, a Quad SLI system needs a well-ventilated system case or the graphics cards may just overheat. This is a problem for computer integrators, though, because GeForce 7900 GX2 aren’t yet selling individually.

The slits in the graphics card’s mounting bracket seems to imply that the hot air is exhausted outside of the system case, but this is not implemented despite the correct orientation of the airflow from the top cooler. The reason is that there’s no air-directing casing on the way between the heatsink and the bracket. We guess they just installed a standard bracket from the GeForce 7900 GTX here.

By the way, it is possible the diagonal placement of the connector that links the top and bottom PCBs is due to cooling efficiency considerations. Oriented like that, the connecting card turns the airflow from the bottom cooler by 90 degrees and drives it away from the graphics card.

There are special projections at the external side of the cooler’s aluminum casing with which it contacts the memory chips, via heat-conductive pads. It also cools the X48 switch chip. The traditional dark-gray and very thick thermal paste is used as thermal interface here.

Overall, the cooling system of the GeForce 7900 GX2 is a compromise between cooling efficiency and compact size. The developers had to work within the limits imposed by the design features of this graphics card. The cooler should do its job well considering the low heat dissipation of the G71 chip, but you are not guaranteed a comfortable level of noise. The fans will probably have to work at increased speeds to cool the graphics processor and the memory chips in such cramped conditions.

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