Thanks to the GeForce 7950 GX2 at the heart of BFG’s latest offering, you can now build a dual-GeForce rig using any PCI Express-compliant motherboard—including CrossFire and Intel models.
As much as the 7950 GX2 sounds like SLI in a single slot, nVidia pointedly does not describe it as such. The company is also not allowing the do-it-yourself crowd to use two GX2s to build their own quad-SLI systems. And that’s fine with us: The current crop of 30-inch panels that would render quad SLI worthwhile aren’t fast enough for gaming anyway.
Architecturally, the 7950 GX2 resembles the 7900 GTX: It’s outfitted with 24 pixel-shader units and eight vertex-shader units, and is paired with 512MB of GDDR3 memory. In order to maintain reasonable thermals, however, the core is clocked at just 500MHz and the memory runs at 600MHz. Factory-overclocked models were coming onto the market as we went to press, but this BFG card was clocked the same as nVidia’s reference design. Specs like those would have been big news six months ago, but they’ve become commonplace lately. What’s not so common is the fact that every 7950 GX2 card has two of these puppies.
A GX2 card is formed by bolting together two PCBs, but only one has a PCI Express edge connector. A proprietary PCI Express switch on the second PCB handles communication between the two processors and interactions with the host PC’s PCI Express bus. Although each board has its own cooling fan, the GX2 is whisper-quiet. There’s a pair of Dual-Link DVI connectors, but as with conventional SLI, output to the second DVI connector is shut down while running in dual-GPU mode. There is S- and component-video output, but no video input.
DRM COMES TO VIDEOCARDS The 7950 GX2 is one of the first videocards to feature the HDCP technology required to play copy-protected Blu-ray and HD-DVD movies. HDCP requires each component in the digital playback chain—the disc drive, the videocard, and the display—to be outfitted with a crypto-ROM that stores a set of encryption keys. These encryption keys are also stored on each copy-protected Blu-ray and HD-DVD disc. Keys are exchanged at each stage of digital playback: from the disc to the drive, from the drive to the videocard, and from the videocard to the display. If at any point in the path this handshake fails to take place, the sending device can refuse to pass on high-definition data in digital form.
One obvious problem with this DRM scheme is that the vast majority of digital displays in use today are not HDCP capable, which will force users to revert to analog video connections (VGA or component) in order to enjoy high-definition video. But there’s an aspect of AACS that’s capable of blocking that avenue, too: It’s called the Image Constraint Token (ICT). Discs encoded using ICT will restrict video output to a maximum resolution of 960x540 the moment the HDCP chain is broken. There are rumors that the ICT won’t be enabled by Hollywood studios until after 2010, but no official word has come down.
What’s even more troubling about HDCP, however, is the fact that if any device in the playback chain—or even an entire model line—is ever determined to have been compromised, meaning its copy-protection has been hacked or otherwise defeated, it can be placed on a blacklist that gets written to newly manufactured copy-protected discs. These discs will then refuse to send high-definition digital data to any device in that blacklisted family.
SO HOW FAST IS IT? The benchmark chart shows that the 7950 GX2 easily lives up to nVidia’s claim that its the fastest single videocard on the market. Considering it has two powerful GPUs, how could it not be? BFG’s card had no trouble outrunning a solitary overclocked 7900 GT and a single overclocked 7900 GTX. It beat up on a single stock X1900 XTX, too. But the GX2 had a tougher time challenging two high-end cards running in either SLI or CrossFire mode. For instance, it outclassed a matched pair of overclocked 7900 GT cards running in SLI in only one test: Quake 4. Two 7900 GTX cards in SLI, meanwhile, absolutely crushed the single GX2; as did two X1900 XTX’s in CrossFire.
We think the 7950 GX2 is a compelling value, especially if you don’t have an SLI or CrossFire motherboard. The overclocked EVGA 256MB 7900 GT cards (600MHz core, 800MHz memory) used in our comparison were selling for $360 each at press time, so a pair would cost $110 more than BFG’s card and would provide only half the video memory. Meanwhile, the least-expensive 7900 GTX cards we could find were fetching $466 each, or $932 per pair. An ATI X1900 XTX with a matching CrossFire master card costs even more. It’s more difficult to place a value on the GX2’s HDCP feature, however, because it’s unclear whether it will ever be necessary.
Month Reviewed: September 2006
+ TWO BRAINS: The fastest single videocard money can buy.
- TWO HEADS: Can't run two displays in dual-GPU mode; not as fast as two high-end cards in SLI or CrossFire.