AMD overclocks new Phenom II X4 to 7GHz

While 7GHz was achieved with extreme cooling, AMD says overclocking up to 3.8GHz for the 3.2GHz X4 955 is safe at home

AMD on Thursday introduced the latest member of its Phenom II X4 family of high-performance quad-core CPUs, which the No. 2 chip maker said it had run as fast as 7 GHz in extreme overclocking tests.

Out of the box, the new X4 955 Black Edition, which is aimed at gamers and hobbyists, runs at 3.2GHz, giving it similar performance to Intel's fastest desktop chips at lower cost, AMD says.

However, AMD was able to more than double the CPU's speed during its tests, said Brent Barry, an AMD product manager.

The Web site notes that hobbyists with early access to the X4 955 chip have been able to clock it at up to 6.7GHz.

At the International CES in January, AMD demonstrated its then top-of-the-line X4 940 running at 6.5 GHz. ( Watch the YouTube video.)

Key to achieving such speeds is the use of exotic cooling materials, primarily liquid nitrogen and liquid helium.

Barry said liquid nitrogen can help bring PC systems down to about -140 degrees Celsius. Liquid helium is even more potent, able to bring systems down to about -240 degrees Celsius, which starts to approach absolute zero (-273 degrees Celsius).

Liquid helium, however, is much trickier -- and more dangerous -- to work with than liquid nitrogen and other more conventional coolants used by home overclockers, including water or air, said Davis.

The amount of helium required is huge. To cool a PC for 90 minutes requires 250 liters of liquid helium inside a aluminum vat the "size of a VW Beetle," Davis said. The helium is kept under such high pressure that a leak has the potential to push all of the other gases out of the room and asphyxiate anyone inside.

"This is fairly insane, science experiment stuff," Davis said.

Technically, AMD's warranties don't cover chips damaged by overclocking. But AMD offers software such as its OverDrive application to make it easier for their chips to be safely overclocked. And the company says that the 3.2GHz X4 955 should be able to easily operate at up to 3.8GHz using conventional fan cooling.

The X4 955 will cost $245, which AMD says is about 10% cheaper than Intel's 2.83 GHz Core 2 Quad Q9550 processor, which costs $270; and 15% cheaper than the Nehalem-based 2.66 GHz Core i7 920, which costs $289.

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