Maximum PC dual gpu RSS Feed

Gigabyte GeForce 9800 GX2

Michael Brown — Thu, 01 May 2008 16:20:57 -0500

Compared to AMD’s gracefully engineered Radeon 3870 X2, Nvidia’s GeForce 9800 GX2 (represented here by Gigabyte’s implementation) is something of a kludge. But when we consider the performance that Nvidia’s design delivers, it’s hard to complain about elegance.

Both AMD’s and Nvidia’s solutions deliver dual-GPU performance from a single PCI Express slot without requiring chipset support (and in both cases, adding chipset support allows you to run four GPUs in one system). AMD’s solution, however, plants two Radeon 3870 GPUs and two 512MB frame buffers on a single printed circuit board; Nvidia’s design entails taking two PCBs (each with a G92 processor and 512MB of GDDR3 memory), bolting them together, and sticking a ribbon cable in between. It’s a quick-and-dirty brute-force solution, but it delivers frame rates like nobody’s business.

Gigabyte hewed closely to Nvidia’s reference design, clocking the GPU cores at 600MHz, the shaders at 1.5GHz, and the memory at 1GHz. Pay no attention to what Nvidia’s website says, the chip’s memory interface is 256 bits wide, not 512. It seems both Nvidia and AMD have realized that wider interfaces weren’t delivering as much performance as they had anticipated; these days, 256-bit memory interfaces are de rigueur even at the high end.

We’ve given up benchmarking Crysis at 1920x1200, and no card has yet delivered what we’d call acceptable performance even with the 1280x720, 2x AA settings we’ve been using—until now: The 9800 GX2 pumped out 41.4 frames per second.
Maximum PC readers don’t live by games alone, and you obviously don’t need two G92s to watch a Blu-ray movie, but we’re happy to report that the 9800 GX2 includes Nvidia’s excellent PureVideoHD for offloading high-definition video decoding from the host CPU. The HDMI socket on the mounting bracket saves you from having to use an adapter, but getting digital audio to that connector involves another kludge: a cable from your motherboard header to a socket on the card (AMD’s solution routes digital audio over the bus).

But if we can’t have both, we’ll take beast over beauty any day of the week.

MSI R3870 X2 T2DIG

Michael Brown — Mon, 03 Mar 2008 18:54:01 -0600

AMD’s Radeon HD 3870 is a fine GPU for the money. It doesn’t outperform Nvidia’s GeForce 8800 GTX, and it lags far behind the extravagant 8800 Ultra, but it does deliver a phenom— er, make that a tremendous price/performance ratio.

So what happens when you put two of these parts—each with its own 512MB frame buffer—on a single board? You get a Radeon R3870 X2. The result isn’t as spectacular as you’d expect, but MSI’s implementation delivers plenty of bang for the buck. This card isn’t an Ultra killer by any means, but with a price tag of just $450, it doesn’t need to be.

There’s nothing mysterious about the R3870 X2—the two GPUs are exactly the same as those on a single-GPU card. Each one has 320 stream processors, a 256-bit memory interface, support for AMD’s Unified Video Decoder (for offloading HD and Blu-ray video-decoding from the host CPU), and dual-link DVI with HDCP on both links (to support the native resolution of 30-inch LCD panels).

If you care as much about high-definition video decoding as you care about gaming, you probably know that neither Nvidia’s 8800 GTX nor its 8800 Ultra supports those last two features. And unlike Nvidia’s new GPUs that do fully offload HD video decoding, the R3870 X2 supports the incremental updates to DirectX: Direct3D 10.1 and Shader Model 4.1 (although we believe this support to be unimportant right now).

MSI set the GPUs’ cores to run at 828MHz and the memory at 955MHz, a fraction faster than AMD’s reference-design specs of 825MHz and 900MHz, respectively. As with AMD’s 3870 X2 reference design, MSI’s board has two 512MB frame buffers, one for each GPU. AMD’s reference design and MSI’s implementation both use GDDR3 memory, compared to the GDDR4 memory found on single-GPU 3870 cards. AMD tells us there’s nothing about the design that would prevent its board partners from using GDDR4 memory or from increasing the size of the frame buffers (although we suspect there wouldn’t be a tremendous difference in performance from either design change).

A PCI Express 1.1 bridge chip sitting between the two processors effectively creates CrossFire on the card (with 16 bi-directional lanes for each GPU) without the need for a CrossFire chipset on the motherboard. There is, however, a single interconnect that will allow you to build a CrossFireX rig with four 3870 GPUs onboard, but that does require a CrossFire chipset. The board itself supports PCI Express 2.0, but AMD tells us that putting a PCI Express 2.0 bridge chip between the two GPUs would have delayed the product and wouldn’t have yielded much of a performance boost anyway.

Having all the components on a single board strikes us as a much more elegant solution than sandwiching boards together, which Nvidia did with its since-discontinued 7950 GX2. It also allows AMD to use a single cooler, which is located at the very end of the board and exhausts outside the case, for both GPUs and both frame buffers.

You’ll need both the six-pin and eight-pin power connectors if you intend to overclock a 3870 X2 board.

Having a single fan not only renders the card nearly as quiet as a single-GPU configuration but also avoids the need for twice the electrical power. The R3870 has two auxiliary power sockets onboard, one six-pin and one eight-pin, but only the six-pin socket is needed for normal operation. If you intend to overclock the board, you will need to send power to both of them. In our tests, our 3870 X2 test system consumed about 170 watts at idle and around 275 watts under load, compared to the 3870’s 117 watts at idle and 208 watts under load.

We periodically update the games we use for videocard benchmarking, but we’ve stuck with the Shader Model 3.0 tests in the artificial benchmark 3DMark06 as a means of providing continuity. The results we’ve seen with the 3870 X2, however, indicate that the benchmark has finally outlived its usefulness: The 2x performance boost it delivers there doesn’t jibe with the frame rates we saw in actual games. In fact, there was virtually no performance scaling in Crysis at all with the 3870 X2 when compared to a single Radeon 3870.

The 3870 X2 is a good solution, but it doesn’t solve the fundamental problem with dual-, tri-, and quad-GPU systems: Their performance doesn’t scale with every game—including high-profile titles like Crysis that you’d buy these cards for in the first place.

BFG GeForce 7950 GX2

Michael Brown — Wed, 12 Jul 2006 16:06:47 -0500

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.

VERDICT: 9
kickass=yes

URL: www.bfgtech.com