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ATI X1900 CrossFire


ATI X1900 CrossFire

Less than four months since we reviewed the Radeon X1800 XT, ATI has followed up with a successor, the R580, now bestowed with the title X1900. This means that the X1800 has had one of the shortest ever runs as a flagship graphics product, beaten only by NVIDIA’s ill-fated and ill-rated, GeForceFX 5800. However, as ATI would have had two teams working on new products, it’s likely that the R580 team were simply on-time, whereas the R520 team, were clearly very late. Even more remarkably, it seems as though ATI hasn’t entirely paper launched and its cards should be available to buy as you read this. Two cards are available today: the X1900 XTX and the X1900 XT. However, clearly the old ways are hard to part with and no retailers have any X1900 XT CrossFire Editions on their virtual shelves, so our CrossFire test setup is not yet available to buy.

Looking at the spec of the new cards, it really brought home the fact that the computer industry growing up. Just a few short years ago it was all about the Megahertz; now everyone’s getting all touch-feely with talk of ‘Performance per Watt’ and ‘efficiency’. At the launch of the R520, ATI was very much stressing the latter, claiming that it wasn’t how many pixel pipelines you had but what you did with them that counted. Of course, it was rather too easy to be cynical about the reason it was taking up this position. After all, its competitor’s top-of-the-line card, the GeForce 7800 GTX, had 24 pixel pipelines, while its card had only 16.

However, judging from the specs of its new flagship product it seems to have stuck to its guns. Instead of keeping up with the Jones’s and offering 24 pixel pipelines, it’s rearranged them internally to make them a lot more, well - efficient. The part is again built on TSMC’s 90nm process, but the figures that will be taking the headlines are the massive total transistor count of 380m and the fact that the pixel processors have increased from 16 up to a massive 48. However, the X1900 can’t be simply labelled a 48 pixel pipeline part.

To understand this, lets first take a simplified look at the pixel pipeline. This consists of the pixel shader processors, the texture units, the vertex shaders, and the raster operators, ROPs, the latter being the part that deals with rendering the pixels onto the screens. Up to now the 7800 GTX has been the widest part internally, with 24 pixel processors combined with 24 texture units.

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