If you take a double-barreled shotgun and duct tape another double-barreled shot to it, do you get double the performance or do you find your ass planted firmly on the ground with the buckshot scattered? That’s what we wondered when AMD sent us its new Radeon HD 3870X2 running in CrossFireX mode. That’s a total of four GPUs in the system.

For those who don’t know, AMD’s Radeon HD3870X2 is the company’s second generation dual-GPU card. The first, the Rage Fury Maxx, was introduced before the turn of the century. Unlike Nvidia’s GeForce 7950GX2 card which sandwiched two separate PCBs together to form a “single” dual GPU card, the Radeon HD3870X2 features both GPUs on the same PCB. Each GPU features 320 stream processors, a 256-bit memory interface, a unified video decoder and a 512MB of GDDR3 frame buffer for each GPU. The card also supports DirectX 10.1 and Shader 4.1 for future proofing.

For this preview, Alienware supplied its top ALX gaming PC equipped with two Radeon HD 3970X2 cards. Also stuffed into the ALX were: a water-cooled, 3GHz Intel Core 2 Extreme QX9650 overclocked to 4GHz, 4GB of Patriot DDR3/1800, and an X38-based Asus P5E3 Deluxe motherboard. The cards were each clocked at the stock speeds for the HD 3970X2: 825MHz core and 900MHz memory.

We ran three benchmarks: Call of Duty 4, 3DMark06 and Unreal Tournament 3 for our tests. We initially planned to test using Crysis as well, but ended up chucking it as a benchmark due to sporadic stability problems that we couldn’t explain.

What’s the quick verdict? Benchmark results scaled surprisingly well when we moved from two-GPUs (in a single 3870X2 board) to four GPUs (in a pair of 3870X2s).The caveat, of course, is that you’ll need to play your games at ultra high resolutions to really see the difference. But even at 1920x1200 – the standard resolution of most 24-inch flat panels, you can see a frame rate increase of roughly 20 percent by dropping a second 3870X2 board in your rig. When you step up to a 30-inch panel, the four GPUs in the 3870X2 come into play with roughly a 40 percent increase in frame rate.

That’s not too shabby. It also erases reservations we’ve had about quad GPUs since Nvidia tested its dual-GPU GeForce 7950GX2 cards two years ago. Then, buggy drivers and difficulties getting games to support the high resolutions pretty much destroyed Quad SLI. Lack of Vista drivers didn’t help either. Things have changed for ultra-high resolution gaming now though. With the price of 30-inch panels coming down and 3870X2 boards available for an almost affordable $450 each, we’re genuinely excited about the technology.

However, the 3870X2 won’t be the only quad-GPU game in town for long. Nvidia has its own second-generation Quad SLI in the works. Still, the performance of the 3870X2 in CrossFireX makes us feel a bit more comfortable that at least those two extra GPUs aren’t goldbricking—at least at high resolutions.

There’s still work to be done to improve stability with AMD drivers, which is why this is a preview and not a review. The company also freely admits that the scaling is best under DirectX9. DX10 performance currently to top out at three GPUs, the company says. The company says that that problem is a driver issue that it expects to fix. For now, the ball goes back to Nvidia.

A version of the 3870X2 driver enabling CrossFireX will be publicly available March 5th.

BENCHMARKS
	CrossFireX	Single Card	Percent difference
3DMark Overall 12x10, DX9	22,890.0	20,094.0	12.2%
3DMark Overall 25x16, DX9	21,050.0	12,889.0	38.8%
3DMark06 HDR1 Canyon Flight 26x16, DX9	52.7	30.0	43.1%
3DMark06 HDR2 Deep Freeze 26x16, DX9	51.3	26.0	49.3%
3DMark06 HDR1 Canyon Flight 19x12, DX9	85.3	43.7	48.8%
3DMark06 HDR2 Deep Freeze 19x12, DX9	79.9	41.0	48.7%
Call Of Duty 4 25x16, DX9	93.0	73.0	21.5%
Call Of Duty 4 19x12, DX9	140.0	73.4	47.6%
Unreal 3 CTF-OmicronDawn_bot 25x16, DX10	118.0	65.6	44.4%
Unreal 3 CTF-OmicronDawn_bot 19x12, DX10	143.6	105.0	26.9%
Unreal 3 CTF-OmicronDawn_bot 25x16, DX9	120.3	68.5	43.1%
Unreal 3 CTF-OmicronDawn_bot 19x12, DX9	136.0	108.0	20.6%