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NVIDIA GeForce 7900 GX2 1GB Quad SLI Review |
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Written by Mavke
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Monday, 01 May 2006 |
Coming from techPowerUp! is a review on the NVIDIA GeForce 7900 GX2 1GB Quad SLI graphics card. At this year's CeBIT the most controversial and most debated new hardware was NVIDIA's Quad SLI, which was awarded best product of CES earlier this year. By now everybody should know about SLI which combines the rendering power of two video cards to achieve greater performance, or better image quality through higher Anti-Aliasing levels. The logical evolution of this dual solution is using four GPU's. However, since there are no chipsets and/or motherboards which support PCI Express x16 on four slots, NVIDIA had to come up with a way to make their idea happen.
 NVIDIA GeForce 7900 GX2 1GB Quad SLI Review
In the past we have seen dual GPU solutions on one PCB from manufacturers like Gigabyte or ASUS. But these were just GeForce 6600 designs which were not using such complex PCB's. The GeForce 7900 GTX is the biggest and baddest NVIDIA card around, of course it has a completely different range of requirements when it comes to power and signal stability. So putting two GPU's on one PCB was out. The clever people at NVIDIA worked up a rather simple but ingenious solution, just stack two video cards, let them use only one slot connector and interconnect them with an own PCI Express bus.
This brings us to another problem. Since the consumed power does not do any physical work, well except for the fans, it is dissipated as heat. And there's lots of it. NVIDIA uses a low-profile fan on each GPU. This means that each video card has its own fan, so the total number of coolers is four. But to stay within their thermal budget NVIDIA had to reduce the clock rates of the GeForce 7900 GX2 down to 500MHz core and 1200MHz memory from the GeForce 7900 GTX's original 650/1600MHz. Each SLI card has 512MB of memory per GPU, which means that one GX2 card has 1GB memory onboard.
Obviously one GeForce 7900 GX2 card is a double-height card. Because of its length it may be hard to install in some cases because there's very little space. What is important with the PCB design is that the two card parts are interconnected by its own PCI Express bus and its own SLI connector. We could overclock our GeForce 7900 GX2 cards to a maximum of 585MHz core and 1460MHz on the memory which is very good. Considering the design it may be possible that some waterblock vendors come out with GX2 water blocks soon, from an engineering perspective it seems not too hard to do.
When I first heard about the opportunity to play with Quad SLI versus CrossFire I expected Quad SLI to have a significant advantage over CrossFire but at an equally significant price difference. Now I am very disappointed. The driver installation seems to be very unstable. Also it seems nobody tested these cards on an ASUS board, where you have to change a BIOS setting to get the cards stable. The performance is absolutely not what you would expect from a technology leader, best of CES product. In some benchmarks two ATI video cards were a great deal faster.
Even more humiliating was that one single GeForce 7900 GX2 often runs faster than two GX2 cards in Quad SLI. Over the years NVIDIA's has greatly improved their SLI drivers to be rock stable and very performance efficient. If they can do the same to their Quad SLI drivers I think we will see a winner. But until then you better wait till the quirks are sorted out. Quad SLI seems to be a very promising solution. Hats off to the engineers who managed to put so much GPU power into so little space without any thermal or power issues.
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