The Radeon 9800 XT is based on ATI's R360 chip, which is essentially a minor revision of the R350 chip used in the Radeon 9800 Pro. The chip is still fabbed by TMSC using 0.15-micron process technology. ATI has modified R360 silicon in order to clean up some trouble areas and to allow for higher clock speeds. Beyond that, the R360 has all the familiar R350 features, including support for floating-point pixel formats, programmable shaders, and F-buffer logic that enables longer shader programs without conventional multipass rendering. With the tweaks, the Radeon 9800 XT has reached new highs: a 412MHz core clock speed with an effective 730MHz clock speed on its DDR memory. That's just a step or two up from the 380/700MHz core and memory speeds of the 9800 Pro 256MB.
Other changes from the Radeon 9800 Pro to the XT are similarly simple. The 9800 XT card is a new circuit board design, visibly distinct from the 9800 Pro 256MB. Also, to keep the R360 chip cool at its higher clock speeds, the Radeon 9800 XT comes stock with a fancy new copper cooler, like so:
This new cooler is larger and heavier than the almost-wimpy heatsink/fan combos on previous Radeon 9800 cards, but it's nothing compared to the massive hunks of metal strapped to every GeForce FX 5900 Ultra. The larger fan on the XT's cooler varies its speed according to chip temperatures. It runs a lower speeds during normal use, and kicks up to a faster speed when the R360 chip gets a workout. Running full tilt, the XT's cooler isn't horribly loud, but it's definitely audible. When it's rotating slowly, the fan is nearly silent. Of course, the same could be said for the cooler on the Radeon 9800 XT's primary competitor; the GeForce FX 5900 Ultra's blower is quiet at low speeds, and not too terribly loud going flat out.
With the new cooler, new PCB layout, and tweaked silicon, ATI says the 9800 XT is more overclockable than its forerunner, although we haven't had the card long enough to test that theory just yet.
As you can see in the pictures, the 9800 XT comes with the standard array of outputs: one VGA, one DVI, and one video out. We've long wished to see these top-end cards come with dual DVI outputs and a pair of adapters for VGA, but apparently neither ATI nor NVIDIA has gotten that message yet. Hope springs eternal here at TR, though, so we'll keep mentioning it.
The clock speed equation
The higher clock speeds of the Radeon 9800 XT mean better performance, particularly in the pixel-pushing department. From simple pixel filling to complex programmable pixel shader effects, the primary bottlenecks to all-out performance in graphics today are related to pixel pushing. The Radeon 9800 XT is all about high resolutions and a healthy dose of (both edge and texture) antialiasing in current games, plus fluid frame rates in next-generation games. To get a sense for what the 9800 XT brings to the table, let's bust out one of our world-famous chip charts.
|Core clock (MHz)||Pixel pipelines||Peak fill rate (Mpixels/s)||Texture units per pixel pipeline||Peak fill rate (Mtexels/s)||Memory clock (MHz)||Memory bus width (bits)||Peak memory bandwidth (GB/s)|
|GeForce FX 5800 Ultra||500||4||2000||2||4000||1000||128||16.0|
|Radeon 9700 Pro||325||8||2600||1||2600||620||256||19.8|
|Radeon 9800 Pro||380||8||3040||1||3040||680||256||21.8|
|Radeon 9800 Pro 256MB||380||8||3040||1||3040||700||256||22.4|
|Radeon 9800 XT||412||8||3296||1||3296||730||256||23.4|
|GeForce FX 5900 Ultra||450||4||1800||2||3600||850||256||27.2|
With another 32MHz over the Radeon 9800 Pro, the 9800 XT theoretically improves on its predecessor only a tad, but the 9800 Pro was already a behemoth. I won't go into all the dynamics of it, because you can read the chart yourself, and because we'll be testing things here in a moment.
Note how the Radeon 9800 XT matches up against the GeForce FX 5900 Ultra. With eight pixel pipes, the XT blows it away in pixel fill rate. The 5900 Ultra is faster with multitexturing, however, and has even more memory bandwidth than the XT. In these simple, theoretical measures, it's a tight race.