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Diamond's Radeon HD 2900 XT 1GB graphics card

GDDR4 rides again

IF YOU'VE BEEN PAYING attention, you probably already know that AMD elected not to reach for the overall graphics performance crown when it introduced its new generation of Radeons, including the flagship Radeon HD 2900 XT. Instead, the company chose to target the $399 mark, where the 2900 XT would compete against the GeForce 8800 GTS. This was a surprising move, indeed—practically without precedent in the modern GPU race.

AMD did it for solid reasons, of course, including the fact that its new graphics processor wasn't quite up to the task of taking on the GeForce 8800 GTX head to head. That makes the product we're reviewing today all the more interesting, because it's a souped-up version of the Radeon HD 2900 XT with a full gig of screaming fast GDDR4 memory. AMD has practically kept mum on this product, choosing not to point out its existence or highlight it in any way. But Diamond and a handful of other AMD partners have been shipping the cards to PC makers for a few weeks now, and contrary to the initial plan, cards are quietly beginning to show up at online retailers, as well.

This card, with a staggering 128 GB/s of memory bandwidth, raises a number of intriguing questions about the role of memory bandwidth, the question of graphics memory size (how much is enough?) and most of all, the potential of AMD's R600 GPU. Some time has passed since the 2900 XT's debut, drivers have had time to mature, and here we have a faster version of the card. Can this new 2900 XT take on Nvidia's best? Are the matchups altered in DirectX 10 games? And how does the UVD-less 2900 XT really perform in HD video playback? Read on for all of these answers and more.

The card
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 GDDR4, 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.

As I've mentioned, AMD initially planned to sell these cards exclusively through system builders, who would presumably stuff them into $5000 PCs painted metallic green. Fortunately, though, individual cards are already starting to show up at online vendors, and Diamond expects its branded cards to be in stock at Newegg soon. Street prices look to be between $489 and $549, which makes this card a fairly direct competitor to the GeForce 8800 GTX.

Oh, yeah. I took some pictures.

Here's a look at the funky eight-pin power plug on the 2900 XT. This plug will accept a six-pin connector, but AMD's Overdrive overclocking utility isn't available unless an eight-pin power plug is connected. I've never seen an adapter to covert another connector type to an eight-pin one, either, so you're probably looking at a power supply upgrade if you want to overclock this card.

These are the "native" CrossFire connectors on the 2900 XT. In case you didn't see the memo, dongles aren't needed anymore.