AMD Radeon HD 6990 4 GB Review: Antilles Makes (Too Much) Noise

Several months late and supposedly only a couple of weeks ahead of Nvidia's own dual-GPU flagship launch, AMD's Radeon HD 6990 has no trouble establishing performance superiority. But does speed at any cost sacrifice too much of the user experience?

In drag racing, they say ‘a chase is a race.’ In other words, if you floor it and the guy next to you follows suit, that’s a race, and you’d better be prepared to pay up at the finish if it’s a money contest.

Both AMD have ridiculous dual-GPU hot rods they’ve been tweaking and tuning for months. Understandably, they want to stay secretive about their respective power plants. But neither one seems willing to mash the pedal and risk an embarrassing second-place finish. It’s a good thing that these two companies don’t live their lives a quarter-mile at a time. I can just see Vin, shaking his head in disappointment.

But come on already, guys! The AMD Radeon HD 6990 was supposed to be a 2010 model, and here we are in March wondering if AMD overpromised during its press briefing last October. We even heard rumours that the 6990 was cancelled.

Au contraire, Pierre. It looks like AMD is making the first move with its blown Charger, daring Nvidia to throw-down with a twin sequential turbo-charged probably know it as the rumoured GeForce GTX 590. We received a single Radeon HD 6990 4 GB one week ago, beta drivers a couple of days later, and updated Catalyst Application Profiles a couple of days after that. Needless to say, the benchmarking marathon that went on in our Bakersfield, CA lab made the 24 Hours of Le Mans look like kart racing at an amusement park.

Meet Radeon HD 6990 4 GB

It just sounds majestic, doesn’t it? 6990. 4 GB. Unlike anything we’ve ever seen from AMD on the desktop. But don’t let naming trickery disarm you like the beautiful rosso corsa of Ferrari’s racecars.

The Radeon HD 6990 follows in the pedigree of Radeon HD 4870 X2 and Radeon HD 5970. It’s a dual-GPU card with graphics processors running, by default, at slightly reduced clock speeds compared to the company’s fastest single-chip board. Its 4 GB of memory are divided between both ASICs. So, you’re essentially looking at two 2 GB configurations on a single PCB, running in CrossFire.

Although it was previously referred to by the code name Antilles, Radeon HD 6990 centres on two of the Cayman-based GPUs found in Radeon HD 6970 and 6950 graphics cards. If you remember from Radeon HD 6970 And 6950 Review: Is Cayman A Gator Or A Crock?, Cayman employs a slightly modified architecture, designed to extract more performance per square millimetre of die space. There are situations where this VLIW4 architecture could underperform AMD's older VLIW5 design, but the company says those situations are rare.

Bottom line: the highest-end Cayman configuration offers fewer ALUs than the most complex Cypress processor (found in the Radeon HD 5800-series cards). However, Cayman’s ALUs are more capable. For a deeper background on Cayman’s architecture, check the second page of our launch coverage.

Each Cayman GPU serves up 1536 ALUs spread across 24 SIMDs. SIMDs are tied to four texture units, totalling 96. Radeon HD 6990 utilizes Cayman in its uncut form, so you get 3072 ALUs and 192 texture units between the pair of GPUs. As mentioned, the 4 GB frame buffer is divided up, 2 GB of GDDR5 per processor, connected via a 256-bit bus.

AMD unifies the two Cayman GPUs using the exact same 48-lane PCI Express 2.0 switch from PLX found on the Radeon HD 5970. Sixteen of those lanes serve the slot interface, 16 go to GPU 1, and 16 go to GPU 2.

Radeon HD 6990
Radeon HD 6970
Radeon HD 6950
GeForce GTX 580
Manufacturing Process
40 nm TSMC40 nm TSMC
40 nm TSMC
40 nm TSMC
Die Size
2 x 389 mm²389 mm²389 mm²520 mm²
2 x 2.64 billion2.64 billion
2.64 billion
3 billion
Engine Clock
830 MHz880 MHz
800 MHz
772 MHz
Stream Processors / CUDA Cores
Compute Performance
Texture Units
Texture Fillrate
159.4 Gtex/s
84.5 Gtex/s
70.4 Gtex/s
49.4 Gtex/s
Pixel Fillrate
53.1 Gpix/s
28.2 Gpix/s
25.6 Gpix/s
37.1 Gpix/s
Frame Buffer
1.5 GB GDDR5
Memory Clock
1250 MHz
1375 MHz
1250 MHz
1002 MHz
Memory Bandwidth
2 x 160 GB/s (256-bit)176 GB/s (256-bit)
160 GB/s (256-bit)
192 GB/s (384-bit)
Maximum Board Power
375 W
250 W
200 W
244 W

Of course, we’re ecstatic that AMD is using fully functional 40 nm Cayman GPUs—the kind you’d find on a Radeon HD 6970. But that product is already rated for up to 250 W maximum board power. Keeping the 6990’s thermal output manageable meant turning down the clocks from 880 MHz (Radeon HD 6970) to 830 MHz (Radeon HD 6990). AMD also uses a lower memory clock (1250 MHz rather than 1375 MHz). The resulting compute power adds up to 5.1 TFLOPS of single-precision math or 1.27 TFLOPS double-precision.

But AMD also arms this card with a couple of surprises that "break the rules" in the name of more muscle.

Create a new thread in the UK Article comments forum about this subject
This thread is closed for comments
Comment from the forums
    Your comment
  • doive1231
    What about 10 display outputs from a Crossfire setup. Yeah!
  • prightiam
    So this thing is actually louder than the dustbuster?!
  • Anonymous
    I'm a bit puzzled by the lack of 580GTX SLi comparison? Once again an incomplete review. Sorry!
  • Sabiancym
    A lot of the people who would get these, including me, would water cool them. So the sound issue is gone.

    These things are beasts.
  • blubbey
    Crysis has finally been conquered. It only took a few years and an absurd amount of power, however =]
  • fruees
    This is why I'd never buy a super-high end card, the ppl that bought the 5990s dropped about £450 4 months ago and now their card isn't even mentioned in the high performance benchmarks!
  • evilgenius134
    frueesThis is why I'd never buy a super-high end card, the ppl that bought the 5990s dropped about £450 4 months ago and now their card isn't even mentioned in the high performance benchmarks!

    The previous card to this is the 5970, and it is mentioned.
  • damian86
    Yes, but still, you can't compare this to nvidias balance between image quality and speed. Radeons balance is unfortunately awful and I cannot see the driver issues getting better,it still need a touch of 'gamer' in software. A few years ago a comparision has been done with both of them and Radeons had a high percentage in causing BSODs.I can still hear people complaining about the drivers...
  • asteldian
    I hate 2 cards in one set ups. This just strengthens my distaste for them. I considered the GTX 480 a monster that should never have hit the shelves, now this beast has turned up, at least it can try and justify itself by being a double carder.
    AMD tend to be a bit sloppy with driver support for games at the best of times, I can only imagine the nightmare these will be
  • Anonymous
    asteldianAMD tend to be a bit sloppy with driver support for games at the best of times

    People say that, but I've never *ever* had a driver issue with ATI/AMD cards in the 10+ years I've been using them.
  • Griffolion
    Impressive stuff but let's wait to see what Nvidia comes out with in the 590. Considering that AMD has broken through the 300W ceiling very considerably, i'd like to see what Nvidia can pull off with a power budget of what the 6990 had.

    I have a 5970, and until games start to slow down that plus my I5 at 4GHz, I won't be buying anything new.
  • Solitaire
    Not just this card but everything based on the same PCB is little better than an engineering sample - its too impractical and I expect most board partners will be cooking up slightly shorter cards and vastly superior cooling solutions. Anyone buying a stock card is either mad or preparing to rip that horrid fan clean off and stick a hugeass waterblock on that card...