It's been over a year since ATI was knocked head-first off its proverbial high-horse, landing in the not-so-soft wake of NVIDIA's total domination (excuse the mixed metaphors). However, with the launch of the Radeon HD3870, and now the HD 3870 X2, ATI has at last begun to claw its way back into the graphics race.

You'll quickly notice the product name has been cleverly chosen; not because it has an X (and we all know X stands for EXTREME!), or that it implies double performance, rather it's because this monster of a card has been installed with two GPUs (graphics processing unit) on the one PCB (printed circuit board). It's not the first time this light-bulb has exploded above the head of a GPU manufacturer. In fact, graphics card manufacturers were trying to double the performances with multi-GPU boards as far back as the Rage Fury Maxx or even the Quantum 3D Obsidian2 X-24 single-board Voodoo 2 SLI. It's a simple philosophy, but hey, it works.

We took a look at a Sapphire Radeon HD3870 X2 that's so fresh off the factory floor it arrived without official packaging. Beyond that, it's in perfect reference condition. At around 266mm, the board rivals NVIDIA's 8800 Ultra, requiring either a larger-than-average PC case or at least some additional space behind the PCIe x16 slot.

Although we're not overly impressed by this fairly bland stab at innovation, it does the job pretty well, rivalling NVIDIA's 8800 GTX bad-boy for performance. What we're essentially talking about here are two RV670 GPUs crammed side-by-side onto one PCB. A PCIe x16 1.1 bridge connects the two GPUs, allowing them to talk in a Crossfire-like manner, effectively making this card a single-board Crossfire configuration. As an added bonus, you can get yourself a motherboard based on the 790 chipset and put two of these behemoths together for a quad-CrossfireX configuration.

The RV670 is the same 55nm (nanometre) GPU that was found on the highly successful Radeon HD3870, such as Sapphire's own Radeon HD 3870. However, there are a few minor changes. For instance, the HD3870 offered a core clock speed of just 775MHz, while the HD3870 X2 offers a more potent 825MHz core clock. On the other hand, the memory clock has been muzzled a little, dropping from 2250MHz (effective) to 1800MHz (effective).

Beyond that, it's just double or nothing. The 320 stream processors are now numbered at 640, there are twice as many texture processing units (32) and there's now a solid TeraFLOP of computer power on demand. However, each GPU has its own 512MB of GDDR3 RAM (there's no plan for a GDDR4 version at this stage) and each GPU uses its own 256-bit memory bus, so don't be fooled by any grand 1GB of memory, with 512-bit memory bus slogans, it's not entirely correct.

Despite there being two fairly high-performance GPUs running a total of 225watts of power in close quarters, the Sapphire HD3870 X2 manages to maintain a fairly respectable temperature. Two heat sinks are made from a blend of copper and aluminium, and they benefit from one fan, which vents its exhaust out through the rear of the case. You'll need two PCIe power cables to power this card. Of course, this card supports DirectX 10.1, which will come into effect with Windows Vista SP1 and also includes all the normal perks of the Radeon HD3870, such as the universal video decoder (UVD), a dedicated video decoder, ATI's tessellation processor and also supports display port, a high-bandwidth solution similar to HDMI. Let's not forget the card is fully HDCP compliant.

In performance tests we got promising results. In DirectX 9 games it was impressive. In Half Life 2, running at the native resolution of our Samsung SyncMaster 245B - 1920x1200, with all settings turned up to the max we got 116fps (frames per second). In FEAR we got 144fps using a resolution of 1600x1200 and all settings at max, and in 3DMark06 the Sapphire Radeon HD3870 X2 scored a solid 13436.

In DirectX 10 tests, we also saw more impressive results than the single GPU solution. In the Call of Juarez DirectX 10 demo it averaged 50.9fps at the default settings (1280x1024) and we saw a reasonably healthy 26fps in the DirectX 10 edition of Lost Planet: Extreme Condition benchmark using 1920x1200 and with all DirectX 10 features turned on. The only test that failed to improve over the single GPU card was Crysis, which even managed to drop a few frames to 10fps.

Overall, it was some impressive scaling and a good challenger for NVIDIA's current monopoly. We're still not convinced by ATI's method of choice (simply doubling the hardware), but for now it works and works well.