In the months leading up to the eventual release of AMD's Radeon HD 2900 XT, rumors and pictures surfaced of several mysterious cards which ultimately weren't released on the Radeon HD 2900 XT's launch day last May. Arguably the most remarkable of these prototype Radeon HD 2900 cards was the 12 inch card with 1GB of GDDR4 memory. Many referred to it as the Radeon HD 2900 XTX as its memory was clocked at 2.0GHz; over 150MHz higher than the Radeon HD 2900 XT. At 12 inches long, the card would have been bigger than anything else on the market, including the GeForce 8800 GTX, and as such it would have had a hard time fitting in some cases. - FiringSquad

Diamond Viper 2900 XT 1GB Graphics Board Review

As a result, the card was intended to be sold by system builders only, who would be able to properly house the card in a case that was large enough to accommodate it. Ultimately though system builders passed, it was just too big and ran too hot, despite its unique cooling. Instead they opted to wait for ATI's smaller version. This card runs at the same speeds, only it ships with the same PCB and cooling found on the Radeon HD 2900 XT 512MB. Basically you get all the benefits found in the original 12 inch card, only in the smaller form factor of ATI's existing Radeon HD 2900 XT graphics card.

We recently got our hands on one of these hot little items manufactured by Diamond Multimedia, the Diamond Viper Radeon HD 2900 XT 1GB. Diamond is currently the exclusive manufacturer of these 1GB cards, so you won't find these cards from board partners like PowerColor and Sapphire, in fact, you won't even find these cards being produced by AMD, this is Diamond's baby at the moment. Officially the card will carry a price tag of $549, making it around $150 more than the Radeon HD 2900 XT 512MB card and placing it solidly in GeForce 8800 GTX graphics accelerator territory.

Not only does Diamond's Viper 2900 XT 1GB sport more memory than your typical Radeon HD 2900 XT card, as we outlined earlier, it's packing 2.0GHz effective memory. As a result, the memory subsystem is capable of delivering up to 128GB/sec of peak bandwidth to the graphics core. Thats an impressive figure that no other GPU on the market can match, but this number can be a little deceiving. The graphics chip runs at 745MHz, 5MHz higher than the standard GPU. That's not really a lot honestly, as these GPU's can really be pushed. It's too bad these GPU's weren't pushed to say, 800MHz or so.

Looking over the benchmarks, there are only a handful of cases where the additional memory found in the Diamond Viper 2900 XT 1GB allows it to truly outperform the 512MB version of the Radeon HD 2900 XT card. Our newest DirectX 10 benchmark failed to take advantage of the additional memory provided by the Diamond Viper 2900 XT 1GB, nor did another new game that's proven pretty demanding on graphics cards. Based on this data, it looks like you really won't see any benefits from the 1GB of memory. And what about the competition from NVIDIA?