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Connect3D's Radeon X1900 GT graphics card

Shake yer pixel shaders

THE RADEON X1900 GT FINDS itself in a precarious situation right about now. Formerly ATI's key offering at $299, the X1900 GT's replacement has recently been announced in the form of the Radeon X1900 XT 256MB. This new hotness is scheduled to hit the virtual shelves of online stores later this week. Meanwhile, ATI is rumored to be preparing a new Radeon model to take on the brand-new GeForce 7900 GS at $199. That leaves the X1900 GT cowering in the shadows of the oncoming wheels of progress.

Fortunately, the turnover in the graphics card market has helped push prices on the Radeon X1900 GT well below three hundred bucks in some places, potentially making it a good value for the sharp-eyed enthusiast who can snag one for the right price. But where, exactly, does the Radeon X1900 GT fit into the performance landscape? We've tested a lot of graphics cards, but somehow, we've never managed to get our hands on a Radeon X1900 GT—until now. The folks at Connect3D were nice enough to let us coax a Radeon X1900 GT out of them on the eve of its replacement, and we've run it through an enlightening gauntlet of synthetic and real-world tests to see how it compares to, oh, fifteen or so competing graphics solutions.

So what really happens when the Radeon X1900 GT shakes its 36 pixel shaders at a very healthy 575MHz? Can it keep up with potent newcomers like the GeForce 7900 GS? We're about to find out.

Radeon X1900 GT: the R580 at 75%
Like a lot of cards in this price range, the Radeon X1900 GT is based on a hobbled version of a high-end GPU. The same R580 graphics processor that powers the uber-fast Radeon X1900 XTX lies under the sleek, single-slot cooler of the X1900 GT, but in this implementation, about a quarter of the R580's functional units have been disabled for the sake of product segmentation. This shader-ectomy leaves the X1900 GT with 36 pixel shader processors, 12 texture address units, 12 Z-compare units, and 12 render back-ends. The X1900 GT can manage a maximum of 384 concurrent threads, down from 512 in the stock R580, as well. One area where the X1900 GT hasn't been hobbled is vertex shader units; all eight of those remain intact.

The end result of ATI's fiddling with its GPU is still a pretty formidable video card. For its version of the X1900 GT, Connect3D clocks the GPU core at 575MHz and mates it with 256MB of GDDR3 memory running at 600MHz—speeds right in line with ATI's recommended specs. That combo leaves the Radeon X1900 GT with 6.9 billion texels per second of fill rate—basically the ability to paint textured pixels on the screen—and 38.4GB/s of memory bandwidth.

Compare that to the GeForce 7900 GS, which can deliver up to 9 gigatexels/s of fill rate and has 42.2GB/s of memory bandwidth at its stock clock speeds. The Radeon X1900 GT has less peak fill rate, but it makes up the deficit in other ways—especially by having lots of computational power in those 36 pixel shader units. As games use more advanced shading techniques, computational throughput tends to matter more than fill rate, so this is no small thing.

Of course, handicapping the comparative power of the Radeon X1900 GT and its competition from the green team can get tricky in a hurry. The current GPU architectures from ATI and Nvidia are sufficiently different that one can't directly compare the 20 pixel shader units in the GeForce 7900 GS with the 36 units in the X1900 GT. Experience tells us that Nvidia's pixel shader units tend to achieve more throughput per clock than ATI's, but that will depend greatly on many things, including the mix of instructions being executed. Also, one of the two main ALUs in the current Nvidia pixel shader unit splits time between executing shader code and handling texturing, while the R580 has separate and independent texture units. Perhaps the best thing one can do in this situation is simply test performance—which is exactly what we've done.

Connect3D's Radeon X1900 GT

Before we move on to the test results, we should take a quick look at Connect3D's version of the Radeon X1900 GT. As you can see, this card comes with the same cooler that also adorns the Radeons X1800 GTO and X1800 XL. This is a much more substantial cooler than the ones you'll find on many new GeForce cards; its blower sends air through the ducted enclosure across an array of very fine copper fins.

The card features dual DVI ports and full video input and output capabilities. Connect3D packages the X1900 GT with a reasonably complete set of cables to take advantage of these abilities, including a composite/S-Video I/O combo cable and a component output cable. They also throw in extender cables for component and S-Video, a power splitter, and a couple of DVI-to-VGA plug adapters. Connect3D hasn't bundled any games with the card, but they haven't skimped on the key hardware accessories, which is the more important thing in my book.