GeForce 7950 GX2 Hands-On Preview

Board analysis (cont’d)

Multimedia users will be glad to hear that all GeForce 7950 GX2 cards are HDCP-compliant. For the first time NVIDIA’s requiring all their board partners to include the crypto-ROM chip that carries the HDCP key that’s required for encoding protected high-definition content. If you recall our HDCP Fiasco article, both the graphics card and monitor must be HDCP-compatible in order to play HD-DVD and Blu-Ray movies at full 1980x1080 resolution. Prior to the GeForce 7950 GX2, only a handful of NVIDIA-based graphics cards shipped with the crypto-ROM chip (which is an extra chip external of the GPU that stores a special crypto HDCP key) mainly in a line of OEM Sony media center PCs as well as an ASUS GeForce 7600 GS card. As we said earlier, this marks the first time NVIDIA has required this of all their board partners. Prior to the GeForce 7950 GX2 this was an optional feature that most board partners elected not to support.

Like previous GeForce 7900 cards, the GeForce 7950 GX2 sports two dual-link DVI connectors.

New cooling

Besides the revised board design, another change NVIDIA’s implemented in the GeForce 7950 GX2 is a new cooling solution. The previous cooler NVIDIA used on the GeForce 7900 GX2 was rather large, and could generate a lot of noise when the board was running under load. The new cooler is considerably smaller and generates less noise than its predecessor, all while keeping the GPU cool.

New cooler on the 7950 GX2

Cooler from an opposite angle

2 Dual-link DVIs

One aspect that’s a little deceiving about both the GeForce 7900 GX2 and the GeForce 7950 GX2 is that while the backplate on these cards have vented holes on it, suggesting that hot air from the GPU exhausts out these holes, this actually isn’t the case, the vents on the back of the GeForce GX2 cards are merely decorative, hot air from the card’s cooler doesn’t exit here. The ducted enclosure NVIDIA uses simply isn’t long enough for hot air to escape through, instead the air passes out the top and left side of the card’s cooler.

Two single slot heatsink/fan units

Another shot of the 7900 GTX and 7950 GX2

Here’s a summary of what’s changed with the GeForce 7950 GX2:

Shorter board design: The GeForce 7950 GX2 measures in at just 9”; about the same length as a GeForce 7900 GTX card. As you’ve no doubt seen in our pictures, this is considerably shorter than the GeForce 7900 GX2.

Running a pair of 7900 GX2 cards for Quad SLI

Note all the cables required to hook everything up...

...In comparison to the 7950 GX2

One power connector: Whereas the original GeForce 7900 GX2 had two 6-pin PCI Express power connectors – one per PCB – NVIDIA’s managed to reduce the number of power connectors to just one total. The result is that less cabling is necessary to power the GeForce 7950 GX2 card, so you don’t have to run multiple power cables to one graphics card anymore.

One SLI bridge connector: On previous GeForce 7900 GX2 cards, two SLI bridge cables were required to run Quad SLI, for the GeForce 7950 GX2 only one SLI bridge cable is needed. NVIDIA mentions that performance is unchanged from the two-connector approach used on GeForce 7900 GX2.

New cooling: The new cooler used on the GeForce 7950 GX2 is smaller and runs quieter than the 7900 GX2 cooler. It seems to do a pretty good job of keeping the GPU cool as well in our opinion.

HDCP: The GeForce 7950 GX2 is the first GeForce GPU to ship with cards that feature out-of-the-box support for HDCP. Previously the GPU supported the technology, but the cards didn’t ship with the crypto-ROM chips that were required to store the HDCP keys. As a result HD-DVD and Blu-Ray discs wouldn’t run at full resolution. NVIDIA’s requiring all their board partners to include the crypto-ROM chip on their GeForce 7950 GX2 cards.

Same clock speeds: The GeForce 7950 GX2 ships with the exact same GPU as the one used in the older GeForce 7900 GX2 Quad SLI cards. The graphics core on each GPU runs at 500MHz, while the memory runs at 600MHz. That’s 150MHz slower on the graphics core than the GeForce 7900 GTX, and 200MHz slower on the memory, so one GeForce 7950 GX2 card will never match the performance of a fully-fledged dual-GPU GeForce 7900 GTX SLI setup, but with two GPUs onboard each GeForce 7950 GX2 card, it’s more than enough performance to best the performance of a single GeForce 7900 GTX card, particularly at high resolutions. With an upcoming ForceWare driver, you can then combine a second GeForce 7950 GX2 card in the future for Quad SLI support. That’s the plan at least.

Keep in mind that you’ll still need an nForce SLI motherboard to support SLI with the GeForce 7950 GX2. If you plug a GeForce 7950 GX2 card into an nForce4 Ultra or nForce 570 Ultra motherboard, the card will work, but only one of the GPUs on the board will function. You’ll need to upgrade to an SLI motherboard if you want both GPUs on your GeForce 7950 GX2 card to operate in SLI mode.

GeForce 7950 GX2 Quad SLI

Quad SLI is still exclusive to OEMs, for now at least

The motherboard’s BIOS

One aspect that NVIDIA’s been stressing concerning the use of the GeForce 7900 GX2 and GeForce 7950 GX2 is that it’s critical that your motherboard have a GX2-compliant BIOS installed prior to use for optimal results. The GeForce 7900 GX2 and 7950 GX2 have a special internal 48-lane PCI Express switch that essentially splits one x16 PCI Express signal into three pieces, 32 lanes are split between the two GPUs present on the GX2 board, while the remaining 16 are used for the PCI Express interface. This allows each of the GPU’s on the GeForce 7950 GX2 to operate at full PCI Express bandwidth while physically only using one PCI Express graphics slot, without this switch you’d need an SLI motherboard with four x16 PCI Express graphics slots to perform this. Not to mention that the nForce chipset would need more PCI Express lanes for Quad SLI.

In any case, the system BIOS of most motherboards is not used to seeing this switch, and while the system may technically work, it may not run with optimal performance and/or stability may be compromised. (This is what we saw with our GeForce 7900 GX2 setup a month ago.) This includes many of the nForce 590 SLI motherboards that were just launched by NVIDIA a few weeks ago. You’ll need to update your motherboard’s BIOS in order to run the GeForce 7950 GX2 card properly. NVIDIA is maintaining a list of GX2-compatible motherboards and the proper minimum BIOS required in order for the technology to work properly at http://www.nvidia.com/gx2, so you’ll want to check this site out if you plan on running a GX2 card in the near future.

Now that we’ve gone over what’s new with the technology, let’s see how it performs…