You wouldn't know this Radeon HD 2900 XT was anything special by looking at it. It looks the same as the original 512MB version, right down to the cheesy metallic flame job on its cooler. Underneath that cooler, though, lies an array of GDDR4 memory chips with double the density of the GDDR3 chips on the original 2900 XT. GDDR4 first debuted on the Radeon X1950 XTX, and at that time, ATI claimed this new RAM type could achieve higher clock speeds while drawing less power per clock cycle. We were somewhat surprised, then, to see Nvidia introduce a while new lineup of world-beating graphics cards without using GDDR3, and we were even more startled when AMD didn't lead off with a GDDR4 version of the 2900 XT.

That card is here at last, though, and Diamond is planning two versions: one with a stock 743MHz core clock and 2GHz memory and another, "overclocked" variant with an 825MHz core and 2.1GHz memory. Both offer quite a bit more memory throughput than the original 2900 XT, whose GDDR3 memory runs at 825MHz; over its 512-bit memory interface, the GDDR3 2900 XT has a theoretical peak of 106 GB/s. Our 2900 XT 1GB GDDR4 card is the slower of the two versions, but it still has 128 GB/s of memory bandwidth, well above the stock 2900XT and astoundingly, almost twice the 86 GB/s of the GeForce 8800 GTX

The 1GB GDDR4 version of the Radeon HD 2900 XT wasn't significantly faster than the original in any of the games we tested, including brand-new DX10 titles and new-ish DX9 titles running at very high resolutions and quality levels. That's bad news for this video card, because it costs as much as GeForce 8800 GTX and performs more like a GeForce 8800 GTS-not the best value proposition.

This weakness is underscored by the fact that the 2900 XT doesn't deliver lower CPU utilization than the GeForce 8800 series when playing back HD movies. AMD made it sound like the 2900 XT would benefit from UVD acceleration, but the GPU simply lacks that capability. In fact, the 2900 XT uses more CPU time during HD video playback than a competing GeForce 8800. AMD's noise reduction and post-processing routines for HD video are superior, however.