No, you’re not seeing double. The Radeon HD 4870 x2 is the latest ATI graphics card to take the contentious ‘two-up’ gamble. As its name rather heavily implies, this behemoth of a card is essentially two HD 4870s rolled into one; providing a significant boost in raw processing power. It’s a concept we’ve seen plenty of times in the past, including last generation’s Radeon HD3870 X2 (which this model is a spiritual successor to). Whether the coins of fate come down in your favour will largely depend on the kind of games you like to play. As it stands, most punters would be better off plumbing for NVIDIA’s single-GPU GTX 280; which offers a bigger bang for a similar asking price.

Based on the same 55nm RV770 chipset as the standard HD 4870 card, the HD 4870 x2 comes with a core clock speed of 750MHz, memory and shader clock speeds of 3600MHz and 750MHz, and a 256-bit memory bus. Beyond that, all major components have been effectively doubled — that’s 1.9 billion transistors, 1600 stream processors, 2.4 teraFLOPS of processing power and 2GB of GDDR5 memory.

Of course, all these specification are slightly misleading, as they are actually spread over two separate GPUs. A PCI express bridge connects the two processors; effectively providing a Crossfire configuration on a single printed circuit board. In short, this means you don’t get double the performance, although the improvement is still significant. ATI has also overhauled its PCI-Express bridge chip, allowing faster data transfer rates of up to 6.8GBps.

We ran our benchmarks on a Vista 32-bit machine equipped with 1GB of DDR2 RAM, a 750GB Barracuda ES hard drive and a 2.66GHz Intel Core 2 Quad CPU. We then compared the results to Asus’ ENGTX280 TOP (HTDP/1G/A) — a factory overclocked card based on NVIDIA's latest GTX 280 graphics chip. (GTX280-based cards retail for around the same price as the Radeon HD 4870 x2, and are currently its chief rival).

The results garnered by the HD 4870 x2 were a bit of a mish-mash to be honest, but we were still quite impressed by its overall performance. In 3DMark 06, the HD 4870 x2 received the highest score we have ever seen when using this test bed — a truly phenomenal 14,430 marks. Asus’ ENGTX280 TOP (HTDP/1G/A) managed a score of 12,724.

In our Half-Life 2 performance test, the HD 4870 averaged a frame rate of 171.2 frames per second, which was eight frames faster than the ENGTX280 TOP (HTDP/1G/A). The game F.E.A.R also fared better on the Radeon card, averaging 194fps (compared to the ENGTX280 TOP’s 154fps). However, when it came to Lost: Extreme Conditions (which happens to be the most recent and graphically demanding game of the bunch), the HD 4870 was seven frames slower than its NVIDIA rival (110fps vs. 117fps).

Our DirectX 10 gaming benchmarks also returned varied results. In Lost Planet: Extreme Conditions (DX10 Edition), the card chugged along at a respectable 56fps; which was eight frames faster than the ENGTX280 TOP. However, the power-hungry Crysis averaged a not-very-playable 23.9fps. This was significantly slower than the ENGTX280 TOP, which averaged 37.32fps.

Our Call of Juarez demo fared a lot better, returning a result of 84.8fps. By contrast, the ENGTX280 TOP averaged 50.9fps — a difference of over 30 frames per second. Despite its average showing in Call of Juarez, the ENGTX280 TOP (HTDP/1G/A) is still the clear winner when it comes to high-end gaming (unless you really dig Call of Juarez, that is).

In terms of design, the HD 4870 x2 is suitably big and chunky. It requires two PCI-E power connectors (6-pin and 8-pin) to run, and has a maximum power rating of 280W. This is definitely on the high side, and can be attributed to its multiple GPUs.