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AMD Acknowledges That Geometry Matters

Radeon HD 6970 And 6950 Review: Is Cayman A Gator Or A Crock?
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When Nvidia first briefed us on the gaming-oriented features of its Fermi architecture almost a year ago, it put the emphasis squarely on geometry. The company argued that modern GPUs have tons of shader performance—and we’d agree. For a flagship graphics card, we have to apply resolutions that most folks can’t even support and multiple monitor arrays just to tax performance. We aren't looking at photorealistic representations of our opponents' lower intestines in Call of Duty yet, but we’re certainly getting there.

Unfortunately, the number of triangles per scene has not kept up. A mountain landscape might be peppered with very real-looking trees and grasses blowing in the wind, but the contours of the environment itself are distinctly geometric—not natural at all. The company purported to solve that issue with its PolyMorph engine—a tessellation unit in each Shader Multiprocessor that’d facilitate scalable performance when software developers started exploiting DirectX 11’s ability to dial up the geometric complexity of a scene.

Tessellation Off: The mountains are so...geometricTessellation Off: The mountains are so...geometric

Tessellation On: So much more realisticTessellation On: So much more realistic

At the time, AMD responded that its own tessellation engine was more than capable of competing with Nvidia’s parallelized implementation. At the time, Unigine’s Heaven benchmark proved that to not be the case. Later, HAWX 2 gave us a real-world example of Nvidia’s architecture scaling better (though not as well as we might have expected, given Nvidia's insistence on the unit's scalability).

With its Radeon HD 6900-series, AMD attempts to bridge the gap with a more focused stab at geometry. When we first looked at the Radeon HD 5870 more than a year ago, we observed that what AMD called dual rasterizers in its graphics engine was actually a rasterizer with a twice as many scan conversion units, upping the pixel throughput to 32 per clock. Now, with the 6900-series’ Cayman processor, you’re still looking at 32 pixels per clock from the rasterizer hardware.  However, AMD essentially duplicated its geometry block in the new architecture (handling transform, setup, backface culling, and tessellation subdivision) adding a bit of load-balancing hardware to help with scaling. At the end of the day, Cayman can handle two triangles per clock, where Cypress (5800 series) and Barts (6800 series) could do one. Additionally, should Cayman’s on-chip caches overflow, as can happen when you’re talking about the extreme number of triangles associated with high tessellation factors, the additional vertices spill over to the frame buffer.

Cayman's Dual Graphics EnginesCayman's Dual Graphics Engines

How does this translate into actual performance? Well, let’s start by running these cards through the same synthetic Unigine tests we’ve used in past reviews:

You can see the new cards do well with tessellation turned off—the 6970 even trumps Nvidia’s GeForce GTX 580. Increasing the tessellation factor hits the AMD boards incrementally harder, though, putting us in the eventual position where a GeForce GTX 480 outmaneuvers two 6850s in CrossFire.

Get past the raw frame rates, though, and we can see that, while the Radeon HD 6900-series boards scale better than the 5800-series cards, improvements made to the Radeon HD 6800s seem to make more of a difference, as the Radeon HD 6870 tops the chart for AMD. Unfortunately for Cayman, that means Nvidia’s approach still yields a better scaling story.

The performance in HAWX 2—really the only shipping game that uses tessellation to improve realism—isn’t much better for the 6900-series cards. The Radeon HD 6970 and 6950 bring up the bottom of the range behind cards like the GeForce GTX 570 and 470.

Check out the scaling chart, though. The Radeon HD 6970, despite losing out to all of Nvidia’s competing cards, comes a lot closer to matching the competition’s scaling profile here, and the Radeon HD 6950 does even better.

It’s interesting that none of Nvidia’s GeForce boards scale based on the number of available PolyMorph engines. They all get stuck around 73% of their performance with tessellation turned on. This is almost assuredly what enables AMD’s cards to “catch up.”

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Top Comments
  • 30 Hide
    terror112 , December 15, 2010 3:13 AM
    WOW not impressed.
  • 15 Hide
    iam2thecrowe , December 15, 2010 4:22 AM
    Dissappointed. well i guess anyone that bought a 5xxx series card that couldnt wait can now be content that they made an ok choice. The only thing i got from this review is that i want 2 x gtx460's or 2 x 6850's, not the new amd cards.
  • 14 Hide
    bluekoala , December 15, 2010 4:56 AM
    I also urge people to put more emphasis on MINIMUM FPS as that is when you require high FPS the most.
Other Comments
  • 30 Hide
    terror112 , December 15, 2010 3:13 AM
    WOW not impressed.
  • 11 Hide
    Annisman , December 15, 2010 3:15 AM
    Thanks for the review Angelini, these new naming schemes are hurting my head, sometimes the only way to tell (at a quick glance) which AMD card matches up to what Nvidia card, is by comparing the prices, which I think is bad for the average consumer.
  • 13 Hide
    rohitbaran , December 15, 2010 3:25 AM
    These cards are to GTX 500 series what 4000 series was to GTX 200. Not the fastest at their time but offer killer performance and feature set for the price. I too expected 6900 to be close to GTX 580, but it didn't turn out that way. Still, it is the card I have waited for to upgrade. Right in my budget.
  • 3 Hide
    tacoslave , December 15, 2010 3:25 AM
    imagine when this hits 32nm?
  • 7 Hide
    notty22 , December 15, 2010 3:27 AM
    AMD's top card is about a draw with the gtx 570.
    Pricing is in line.
    Gives AMD only hold outs buying options, Nvidia already offered
    Merry Christmas
  • 11 Hide
    microterf , December 15, 2010 3:27 AM
    Why drop the 580 when it comes to the multi-gpu scaling??
  • 4 Hide
    IzzyCraft , December 15, 2010 3:28 AM
    Sorry all i read was this
    "This helps catch AMD up to Nvidia. However, Intel has something waiting in the wings that’ll take both graphics companies by surprise. In a couple of weeks, we'll be able to tell you more." and now i'm fixated to weather or not intel's gpu's can actually commit to proper playback.
  • -3 Hide
    andrewcutter , December 15, 2010 3:28 AM
    but from what i read at hardocp, though it is priced alongside the 570, 6970 was benched against the 580 and they were trading blows... So toms has it at par with 570 but hard has it on par with 580.. now im confused because if it can give 580 perfomance or almost 580 performance at 570 price and power then this one is a winner. Sim a 6950 was trading blows with 570 there. So i am very confused
  • -1 Hide
    sgt bombulous , December 15, 2010 3:30 AM
    This is hilarious... How long ago was it that there were ATI fanboys blabbering "The 6970 is gonna be 80% faster than the GTX 580!!!". And then reality hit...
  • 2 Hide
    manitoublack , December 15, 2010 3:35 AM
    I'd have to say wait until the christmas new years dust settles
  • 8 Hide
    andrewcutter , December 15, 2010 3:36 AM
    sry i take back what i said earlier. most reviews agree with what toms says. So my apologies..:) 
  • 6 Hide
    tpi2007 , December 15, 2010 3:36 AM
    Not bad, but not very impressive either. It's hard to be impressed at 40nm by now.

    But it is quite ironic that AMD has had a tesselator in their cards way before anybody supported the feature (let alone Nvidia), and now Nvidia does better tessellation than AMD.. they should really address that problem.. well, now the only way is to redesign the chip... at 28nm.

    28nm it is then, the next big excitment.

    What I would really like, now that the HD6xxx lineup is here (dual GPU still missing, but that is a niche product), is that AMD now focuses on fixing bugs in their drivers.
  • 4 Hide
    namelessonez , December 15, 2010 3:39 AM
    It's always the same story! nVidia pulls out a new product and then the wait begins for AMD to release its products! Ultimately, the difference isn't worth the wait. We know that AMD's winning factor is its price, but nVidia's is the quality....imho!

    As rightly stated, 'reality hits'.
  • 0 Hide
    yyk71200 , December 15, 2010 3:50 AM
    AndrewCutterbut from what i read at hardocp, though it is priced alongside the 570, 6970 was benched against the 580 and they were trading blows... So toms has it at par with 570 but hard has it on par with 580.. now im confused because if it can give 580 perfomance or almost 580 performance at 570 price and power then this one is a winner. Sim a 6950 was trading blows with 570 there. So i am very confused

    Actually, in Hardocp review overall 580 has some edge over 6970 as well. Only in F1 6970 is ahead. 6970 is great value though.
  • 8 Hide
    joytech22 , December 15, 2010 3:52 AM
    IzzyCraftSorry all i read was this"This helps catch AMD up to Nvidia. However, Intel has something waiting in the wings that’ll take both graphics companies by surprise. In a couple of weeks, we'll be able to tell you more." and now i'm fixated to weather or not intel's gpu's can actually commit to proper playback.


    If intel entered the graphics market and provided a half-decent dedicated GPU, that would definitely make ANY GPU company shake in their boots.

    But in all honesty i hope Intel does enter the market for graphics, making AMD and Nvidia push harder and faster for better products.
  • 1 Hide
    Stardude82 , December 15, 2010 3:53 AM
    So the answer to the question posed in the title is that it is neither really a gator nor a crock. It works on so many levels! Well, maybe just one since caimans are more closely related to alligators than crocodiles.
  • 10 Hide
    Tamz_msc , December 15, 2010 3:54 AM
    I wonder if Nvidia will reduce the prices on the GTX 580 and 570.
  • 6 Hide
    Lamiel , December 15, 2010 4:02 AM
    About the only good news I can see in this for AMD is how much they've increased their multi-GPU scaling, making the 6850's in Crossfire a great bargain. That's great, sure, but the new 6900 cards leave me completely underwhelmed. It doesn't make a whole lot of sense to follow up the 6800's in this way. I'm an Nvidia user, but I was still looking forward with curiosity to seeing how much stronger the 6970 would be than the GTX 580. Looks like the hype-machine broke down this time... My guess is that a lot of the AMD/ATI fanatics will be scrambling to salvage some dignity after all their talking up of Cayman and how it would eat Nvidia's lunch.
  • -3 Hide
    fstrthnu , December 15, 2010 4:16 AM
    This reminds me a lot about the recent release of the updated AMD processors - a temporary holdout while the company plans to release new ones ahead. Except these graphics cards don't even have value going for them. Nvidia was behind just a couple months ago, but now they're ready to crush AMD/Radeon. AMD better have something new coming, and FAST. Holding procedures will only do so much when your competitor is already developing their next-gen GPUs.
  • 15 Hide
    iam2thecrowe , December 15, 2010 4:22 AM
    Dissappointed. well i guess anyone that bought a 5xxx series card that couldnt wait can now be content that they made an ok choice. The only thing i got from this review is that i want 2 x gtx460's or 2 x 6850's, not the new amd cards.
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