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Final Thoughts

Wrapping things up, there’s little we need to say that wasn’t already evident in our graphs. The 6990 is a halo card and succeeds at such – by packing two Cayman GPUs on a single card, it is without question the fastest video card on the market today. At the same time there is and always will be a distinction between single-GPU cards and dual-GPU cards; the former is a threat to the latter, but the latter is rarely a threat to the former.

When we reviewed the Radeon HD 5970 back in 2009, the principle question we ran in to was whether it would be better to have a 5970 or two 5850s in CrossFire, given that the two were nearly identical in performance. The answer was that CrossFire was superior so long as you had a power supply with four readily available PCIe power plugs. With the Radeon HD 6990, we find ourselves asking the same question and an even more direct answer. With but a trio of exceptions, the 6990 doesn’t make sense compared to a pair of cards in CrossFire.

The reasons for this are numerous. The 6990 is so close to the 6950CF in performance that on average at 2560 the two are identical. It’s only in Bad Company 2 and Stalker that we see the 6990 take an advantage, which is then negated by anything from Civilization V to DIRT 2. Meanwhile the 6950CF is cooler, significantly quieter, and less power hungry than the 6990. And finally the 6950CF is cheaper: we can snag a pair of cards for $520, versus $700 for the 6990. Likewise, for $640 you can have a pair of 6970s and enjoy performance at 2560 roughly 8% ahead of the 6990, and that setup is still quieter than the 6990.

This leads us to our exceptions, and why we believe the 6990 is truly a niche product.

  1. Quad-CrossFire; this is going to be the highest performing AMD solution at this time, power and noise be damned. This requires a motherboard with PEG slots three slots apart (lest you choke the first 6990), but it’s achievable.
  2. 5x1P Eyefinity. At five-panel resolutions you’re going need a pair of powerful GPUs, but given AMD’s CrossFire Eyefinity limitations at the time only 2 cards can directly drive five monitors: the 5870 Eyefinity 6, and the 6990. Ultimately MST hubs will allow the 6970CF to do this, but for the time being the 6970CF is limited by the number of displays a single card can drive without a hub.
  3. If you absolutely cannot fit two cards in your computer. This is often the traditional domain of the dual-GPU card, but the 6990’s cooling and power requirements put this in jeopardy. Most micro-ATX cases would simply not be suitable due to cooling needs, meanwhile motherboards with two or more PEG slots are increasingly common. There are very few computers with a single PEG slot that could power and cool the 6990 without a complete overhaul in the first place.

Dual-GPU cards have always been a niche product, but the 6990 really takes this and runs with it. There’s no significant power/noise savings to be found by consolidating two GPUs on to a single card, and as we said earlier with the dual-exhaust cooler the 6990 is effectively two video cards on one PCB. This isn’t a bad thing – the 6990 is the world’s fastest video card after all – but it drives the card in to some very specific niches. If you fall in to these niches, then the 6990 is certainly the card for you. At 22% faster than the 5970 it isn’t a massive performance boost, but it certainly has earned its place.

But if you don't fall into these niches, then there’s nothing the Radeon HD 6990 offers you today that the 6950/6970 didn’t offer in CrossFire mode yesterday. In this case while AMD’s king card is an engineering marvel for its ability to handle so much power in a confined space, as a product on the market it won’t be quite as significant as the title implies.

Power, Temperature, and Noise: How Loud Can One Card Get?
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  • smookyolo - Tuesday, March 08, 2011 - link

    My 470 still beats this at compute tasks. Hehehe.

    And damn, this card is noisy.
    Reply
  • RussianSensation - Tuesday, March 08, 2011 - link

    Not even close, unless you are talking about outdated distributed computing projects like Folding@Home code. Try any of the modern DC projects like Collatz Conjecture, MilkyWay@home, etc. and a single HD4850 will smoke a GTX580. This is because Fermi cards are limited to 1/8th of their double-precision performance.

    In other words, an HD6990 which has 5,100 Gflops of single-precision performance will have 1,275 Glops double precision performance (since AMD allows for 1/4th of its SP). In comparison, the GTX470 has 1,089 Gflops of SP performance which only translates into 136 Gflops in DP. Therefore, a single HD6990 is 9.4x faster in modern computational GPGPU tasks.
    Reply
  • palladium - Tuesday, March 08, 2011 - link

    Those are just theoretical performance numbers. Not all programs *even newer ones* can effectively extract ILP from AMD's VLIW4 architecture. Those that can will no doubt with faster; others that can't would be slower. As far as I'm aware lots of programs still prefer nV's scalar arch but that might change with time. Reply
  • MrSpadge - Tuesday, March 08, 2011 - link

    Well.. if you can oly use 1 of 4 VLIW units in DP then you don't need any ILP. Just keep the threads in flight and it's almost like nVidias scalar architecture, just with everything else being different ;)

    MrS
    Reply
  • IanCutress - Tuesday, March 08, 2011 - link

    It all depends on the driver and compiler implementation, and the guy/gal coding it. If you code the same but the compilers are generations apart, then the compiler with the higher generation wins out. If you've had more experience with CUDA based OpenCL, then your NVIDIA OpenCL implementation will outperform your ATI Stream implementation. Pick your card for it's purpose. My homebrew stuff works great on NVIDIA, but I only code for NVIDIA - same thing for big league compute directions. Reply
  • stx53550 - Tuesday, March 15, 2011 - link

    off yourself idiot Reply
  • m.amitava - Tuesday, March 08, 2011 - link

    ".....Cayman’s better power management, leading to a TDP of 37W"

    - is it honestly THAT good? :P
    Reply
  • m.amitava - Tuesday, March 08, 2011 - link

    oops...re-read...that was idle TDP !! Reply
  • MamiyaOtaru - Tuesday, March 08, 2011 - link

    my old 7900gt used 48 at load
    D:

    Don't like the direction this is going. In GPUs it's hard to see any performance advances that don't come with equivalent increases in power usage, unlike what Core 2 was compared to Pentium4.
    Reply
  • Shadowmaster625 - Tuesday, March 08, 2011 - link

    Are you kidding? I have a 7900GTX I dont even use, because it fried my only spare large power supply. A 5670 is twice as fast and consumes next to nothing. Reply

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