AMD has launched the ATI Radeon HD 4870 X2 graphics card that is widely expected to outperform rival nVidia's top-end graphics card, the GeForce GTX 280.

Priced at $549 (£275) in the US, the 4870 X2 is currently available and will be followed by release of the $349 (£175) ATI Radeon HD 4850 X2 in September, AMD said. Both cards have dual graphics processors that are linked using the company's CrossFireX technology and a dedicated bridge chip. CrossFireX allows multiple graphics processors to work in tandem, offering a significant boost in graphics performance.

"We did some driver work, along with this bridge chip, to make this somewhat seamless," said Pat Moorhead, vice-president of advanced market at AMD. "That took a lot of work."

The graphics chips used on the 4870 X2 run at clock speeds of 750MHz, while the chips used on the 4850 X2 run at 625MHz. Another difference lies in the graphics memory used on the two cards. The 4870 X2 has 2GB of GDDR5 memory, while the 4850 X2 has 2GB of GDDR3 memory.

AMD offered a taste of the graphics capability of the 4870 X2 in June, showing reporters at the Computex exhibition a brief, but very realistic-looking, clip of the company's female mascot, Ruby, being chased down a city street by a four-legged robot. The clip was rendered in real time, AMD executives said.

The use of two GPUs is what gives the 4870 X2 an edge over nVidia's GTX 280, which was released in June and has a single graphics chip.

The technology used in the 4870 X2 will likely find its way into other AMD products. One possibility is that a similar graphics processor could be used in Fusion, a family of chips that AMD plans to release starting next year. Fusion processors will incorporate a graphics core into a microprocessor, a feature that AMD is counting on to increase the competitiveness of its future products. However, AMD has yet to reveal what graphics technology will be used in Fusion.

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