With the release of the HD 2900 XT today, the company formerly known as ATI is doing things a little differently. I'm not sure if this is the effect of ATI being a part of AMD now or something else, but different can be good. First of all, the Radeon series has changed the model numbering slightly. Instead of being modelled as X-something, the new GPUs from AMD will now be called HD-something. The one I'm looking at today is the HD 2900 XT. The second thing thats different is that this particular card, which is the first in its series, is not the highest-end graphics card. In the past, ATI and nVidia have always launched their flagship products but AMD is doing things a bit differently. The HD 2900 XT is set to compete against nVidia's 8800GTS and is priced at US$ 399/- for a 512MB version.

Although there is a lot that's new about the HD 2900 XT, it somewhat shares a similar architecture to the X1900 GPU and the Xenos design found inside the XBox 360. For example, the HD 2900 XT features a similar Ring Bus memory controller, however, it is now a 512-bit interface which is a first in the industry- offering over 100GB/sec memory bandwidth. Unlike the x1000 series where the ring bus still featured a central hub, the HD 2900 XT is a fully distributed design with eight 64-bit memory channels.

Also gone are the 48 vector and 48 scalar processing units foud on the x1900XTX- AMD introduces 320 stream processors with the HD 2900 XT that can handle vector or pixel processing. Each of these Superscalar processors can handle 5 instructions/clock cycle pushing a real, measureable 475 GigaFLOPS. Adding two of these GPUs in Crossfire will allow almost a TeraFLOP. Speaking of Crossfire, these HD 2900 XT cards dont need an external dongle and connect internally like the x1950 Pro.

From the Xbox 360 GPU, a programmable tessellation unit makes its way to the HD 2900 XT which allows for geometry data compression that is a lot faster than CPU-based or geometry shader-based tessellation. Basically, this technology applies a sub-division rule to a polygon mesh amplifying animation data/morph targets/deformation models. This allows developers to provide data to GPU at a coarser resolution. Using a Terrain Rendering demo, AMD showed us how 840 triangles were tessellated to 1 million triangles utilizing just 93k memory on the VGA card. If such a terrain was constructed in high resolution using 1.2m triangles, the total buffer size would amount to 55MB!

Lastly, the HD 2900 XT support Direct-X 10 and Shader Model 4.0 for Vista gaming which is now an essential feature for any new GPU. AMD adds a new type of AA called CFAA that is programmable. A future version of DirectX will provide functionality for this. Wrapping it up, the following is a list of specifications for the HD 2900 XT.

Stream Processing Units: 320
Clock Speed: 740 MHz
Math Processing Rate (Multiply-Add): 475 GigaFLOPS
Pixel Processing Rate: 47.5 Gigapixels/sec
Triangle Processing Rate: 742 Mtri/sec
Texture Units: 16
Render Back-Ends: 16
Memory Frame Buffer: 512MB GDDR3
Memory Interface Width: 512 bits
Memory Clock: 825 MHz
Memory Bandwidth: 106 GB/sec
Transistors: 700 million
Process Technology: 80HS
Outputs: D+DL+DVI w/HDCP (HDMI adaptor)

These specs certainly look quite impressive and bring a ton of horse power with them. I feel that one particular screenshot captures the above specs quite nicely and is certainly the most impressive real-time rendering that I've seen. Ruby's lips and skin looked so realistic in this part of the tech demo that AMD showed at their launch event in Tunisia that I was completely blown away.

While the HD 2900 XT GPU is based on the 80nm process, other upcoming members of the family will utilize a 65nm process. Unfortunately, the 700 million transistors on the larger manufacturing process make the HD 2900 XT very hot. Its definitely the hottest card that I've tested in recent times with temperatures hitting over 80ºC under load. I also noticed the fan on the GPU kicking into high gear frequently adding to the noise levels. The good thing is that its a bit shorter in length than nVidia's 8800GTX, although to be fair, AMD is positioning the HD 2900 XT against the GTS which is about the same length as the HD.

Although I've had the card for almost a week, the combination of prior engagements causing me to be out of town as well as the process of building a new testbed based on Vista prevented me from conducting as many benchmarks as I would've liked to. So, using the older testbed that is made up of the X6800 CPU with 2GB DDR2-800Mhz Corsair RAM, I compared the HD 2900 XT in four games. For comparison, I've used the 8800GTX as well as the 320MB and 640MB flavours of the 8800GTS and the X1950XTX.