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Conclusions
The performance race between NVIDIA and ATI is very tight overall, especially at the very high end, when the GeForce 7900 GTX squares off against the Radeon X1900 XTX—close enough that I couldn't declare a clear overall winner. Both cards are incredible performers, and neither of them has shown any great weaknesses in our tests. The 7900 GTX does seem to scale a little bit better in a dual-GPU configuration with SLI than the X1900 XTX does with CrossFire, but we'll have to test CrossFire performance with ATI's new dual 16-lane chipset before drawing any definitive conclusions.

The value propositions for these products will depend quite a bit on how relative street prices shake out in the coming weeks and months. That's especially true for the GeForce 7900 GT. ATI has positioned the Radeon X1800 XL 512MB and the X1800 XT 256MB against it, and we haven't tested either of those configurations yet. Based on what we do know about the performance of the Radeon X1800 XL 256MB and the Radeon X1800 XT 512MB, I'd say the GeForce 7900 GT is in pretty good shape regardless. At about $299, a non-"factory overclocked" model should offer more card for the money than the incumbent GeForce 7800 GT, until now a favorite of ours at this price point.

If you want to talk about real value, though, move a step or two down to the GeForce 7600 GT and the Radeon X1800 GTO. The GeForce 7600 GT, in particular, looks to be a great performer for the price and the new king of the sweet spot in PC graphics, much like the GeForce 6600 GT was before it. The Radeon X1800 GTO offers higher-grade hardware for another fifty bucks, but the 7600 GT achieves equivalent or better performance overall, raising the question of why the GTO should command a higher price. There is, however, one intriguing point that I'd like to note: the 7600 GT came out ahead in our timedemo tests and in 3DMark, but the X1800 GTO was faster in games we measured with FRAPS. I wish we'd had time to test with a broader range of games in order to establish whether this is a trend. We'll have to keep our eyes on that question.

The efficiency issue
NVIDIA has made much of the fact that they have a more efficient GPU architecture than ATI right now, and it's true that NVIDIA's GeForce 7-series desktop GPUs generally achieve higher performance per watt and more performance per die area than ATI's current desktop graphics processors. That's undeniable. Whether and how much this fact matters to you is something you'll have to decide.

Obviously, someone working to build a super-quiet gaming rig or the like will want to take these things into account. GeForce 7600 GT and 7900 series cards will consume less power and throw off less heat inside your PC than their Radeon counterparts. ATI has addressed this problem to some degree by using a dual-slot cooler on its high-end cards that funnels most out air directly out of the back of the case, but at the end of the day, there are few true substitutes for a cooler-running chip.

NVIDIA's smaller chips might also make for less expensive products from NVIDIA and its partners. I would be surprised if the GeForce 7600 GT doesn't make the same migration over its lifetime that the GeForce 6600 GT did, from $199 down to $149 and below. With its much larger die and 256-bit memory interface, the Radeon X1800 GTO isn't likely to make the same transition. ATI will have to replace it with something else, and the Radeon X1600 XT certainly isn't up to the task.

ATI disputes the importance of arcane issues like GPU die size, and at a pretty basic level, they're right to do so. Most folks just want to buy the best graphics card for the money. But ATI wasn't talking down the importance of die size during the Radeon X800 era when people were asking them why they chose to limit their GPU's precision to 24 bits per color channel rather than 32; they were talking up efficient architectures and best use of die area quite eloquently.

The Radeon X1000 series' die sizes are relatively large, of course, because ATI went and built a new architecture with more precision and other new features. Some of those are pretty cool, like the ability to combine high-dynamic range rendering with multisampled antialiasing, or finer granularity for pixel shaders with dynamic branching. From a tech standpoint, the fact that they've decoupled so many stages of the traditional graphics pipeline from one another is pretty slick, too.

Yet I wonder about whether they have struck the right balance of on-chip resources for today's applications or those coming in the near future. The Radeon X1600 XT, for instance, has three times the number of pixel shader processors that it has texture address units and render back ends, as does the Radeon X1900. The Radeon X1800 series, by contrast, has a 1:1 ratio between these units—including the Radeon X1800 GTO. This leads to the odd situation where the Radeon X1800 GTO technically has less pixel shader power than the Radeon X1600 XT. (Both have 12 pixel shader units, but the X1600 XT is clocked higher.) Neither GPU seems to have an optimal ratio of pixel shader power to pixel and texel fill rate for today's games. Judging by what we've seen, the best mix is probably somewhere in between, at a 2:1 or 3:2 ratio. (NVIDIA is at 3:2 for their architecture, but that's a different animal, so comparisons aren't entirely apt.) ATI seems to be casting about a little bit, trying to find the right mix.

I'm curious to see where they'll land, and whether new GPU revisions or upcoming games will make the Radeon X1000 series GPUs look relatively more efficient over time. Whatever happens, they seem unlikely to catch NVIDIA on the efficiency front in this generation of GPUs. How much that matters, it's tough to say—especially in graphics, where the next gen is always just around the corner. 

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