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Radeon HD 6970 And 6950 Review: Is Cayman A Gator Or A Crock?

Radeon HD 6970 And 6950 Arrive

In the world of high-end hardware, waiting for the next great thing means reading about a lot of technology and never actually buying a new piece of gear. That’s no way to enjoy your favorite games though, is it?

Sometimes the wait is worth it, though. Last week was a perfect example. Nvidia launched its GeForce GTX 570, but we already knew AMD’s Radeon HD 6970 and 6950 boards had shipped out, FedEx Next Day Air. How could we not recommend waiting to see how these boards would compare? The very same morning, AMD launched a refresh on its Phenom II and Athlon II processors, incrementing clock rate. But we have Intel’s Sandy Bridge-based CPUs up and running in the lab. Again—why wouldn’t you wait a couple of weeks to see how they stack up?

Anticipating Greatness

I was particularly interested in the performance of the Radeon HD 6970 and 6950, the two cards AMD had shipped so urgently. Whereas the Barts GPUs used to build Radeon HD 6870 and 6850 centered on the same VLIW5 architecture that earned Radeon HD 5870 a place in infamy, the Cayman GPU consolidates functionality into a VLIW4 design, incorporating fewer ALUs per thread processor, but improving performance per square millimeter of die space. How would that translate to the experience you get when you plug a 6900-series card into your system? Well, since Cayman is larger than Cypress, we have to assume it’s also going to be faster.

A market populated by GF100-based boards like GeForce GTX 480 and GeForce GTX 470 would have made this launch so much easier for AMD. But Nvidia has this habit of kicking into gear when it really needs to. The resulting GeForce GTX 580 and 570 demonstrate that, even if Fermi remains a power-hungry architecture, it is possible to contend with more heat using a better sink and finely-tuned fan control. Suddenly, AMD had a much more daunting competitive landscape in front of it.

We’re not sure if that was the real reason AMD’s Radeon HD 6900-series cards were delayed for nearly a month. However, the boards are here now (two of each, actually), and AMD claims that channel availability will be plentiful right out of the gate.

Look familiar? That's the 5870's Cypress

New GPU, Familiar Face

AMD’s GPU team isn’t known for its bold, brash architectural moves—that honor belongs to Nvidia—so it’s hardly a surprise that much of Cayman looks familiar. In fact, there was no fancy press day hosted on an aircraft carrier to herald the improvements, nor were there conversations with chip architects. After the fanfare ahead of Radeon HD 6800, today's 6900-series launch was preceded by surprisingly little commotion. It was almost…refreshing. That gave us plenty of time to dig into the details for ourselves. Fortunately, we know enough about AMD's Cayman GPU to discuss what changes.

Very similar: The 6900-series' Cayman

Fully loaded, the chip features up to 24 SIMD engines (up from Cypress’ 20). Each SIMD still includes 16 thread processors. Except now, each thread processor consists of four ALUs rather than five. So, while Cypress sported as many as 1600 ALUs, Cayman incorporates up to 1536 (that’s 24 * 16 * 4). Each SIMD engine is still tied to four texture units, totaling 96 on a complete Cayman chip (versus 80 on Cypress).

AMD Radeon HD 6970AMD Radeon HD 6950AMD Radeon HD 5870Nvidia GeForce GTX 580
Manufacturing Process40 nm TSMC40 nm TSMC40 nm TSMC40 nm TSMC
Die Size389 mm²389 mm²334 mm²520 mm²
Transistors2.64 billion2.64 billion2.15 billion3 billion
Engine Clock880 MHz800 MHz850 MHz772 MHz
Stream Processors / CUDA Cores153614081600512
Compute Performance2.7 TFLOPS2.25 TFLOPS2.7 TFLOPS1.58 TFLOPS
Texture Units96888064
Texture Fillrate84.5 Gtex/s70.4 Gtex/s68 Gtex/s49.4 Gtex/s
ROPs32323248
Pixel Fillrate28.2 Gpix/s25.6 Gpix/s27.2 Gpix/s37.1 Gpix/s
Frame Buffer2 GB GDDR52 GB GDDR51 GB GDDR51.5 GB GDDR5
Memory Clock1375 MHz1250 MHz1200 MHz1002 MHz
Memory Bandwidth176 GB/s (256-bit)160 GB/s (256-bit)153.6 GB/s (256-bit)192 GB/s (384-bit)
Maximum Board Power250 W200 W188 W244 W

As with the Cypress and Barts GPUs, Cayman is a product of TSMC’s now-mature 40 nm manufacturing process. It probably wouldn’t have been, but TSMC canceled its 32 nm node back in 2009, leaving both AMD and Nvidia to rethink their strategies. The aforementioned specs allowed AMD to keep its die size manageable, while still improving performance, though. Cayman is a 389 mm² piece of silicon composed of 2.64 billion transistors, while Cypress was 334 mm² part made up of 2.15 billion transistors. What AMD didn’t want to do was follow in Nvidia’s footsteps, creating a 500+ mm² behemoth that it’d need to power and then cool. From all angles, Cayman looks to be a compromise based on the hand TSMC dealt.

It seems that the company was able to turn those lemons into something more palatable, though, by getting inventive with a feature called PowerTune, which balances TDP to facilitate higher shipping clock speeds. The two resulting board models, Radeon HD 6970 and 6950 handily outperform AMD’s last at-bat on the 40 nm process. The real question is, can they stack up to the more recent and renewed competition from Nvidia?

Ten points, by the way, if you can figure out the reference in this story’s title.

  • terror112
    WOW not impressed.
    Reply
  • Annisman
    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.
    Reply
  • rohitbaran
    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.
    Reply
  • tacoslave
    imagine when this hits 32nm?
    Reply
  • notty22
    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
    Reply
  • microterf
    Why drop the 580 when it comes to the multi-gpu scaling??
    Reply
  • IzzyCraft
    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.
    Reply
  • andrewcutter
    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
    Reply
  • sgt bombulous
    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...
    Reply
  • manitoublack
    I'd have to say wait until the christmas new years dust settles
    Reply