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Meet The 6990

If you recall our coverage on the 5970, we found a few areas where AMD was lacking. The cooling on the 5970 was sufficient to run the GPUs even at 5870 clocks and voltages, however the cooling on the VRMs was lacking, leading to real world programs trigging the VRM thermal protection mechanism; and while this was within safety guidelines, it’s not a comfortable place to be for long term operation. This ultimately led to us writing off the 5970OC as a 100% reliable product, sticking to recommending the 5970 solely at stock speeds.

The design of the 6990 in turn reads very much like a response to our findings in true engineering fashion. Furthermore for the 6990 AMD not only had to take a look at the 5970’s weaknesses, but also how to handle an even greater power load. The result is that the 6990 is distinctly different from the 5970 before it.


Top: 6990. Bottom: 5970.

Compared to the 5970, the 6990 is ever so slightly shorter, thanks in large part to the fact than the 6000 series casing is more squared off compared to the 5000 series’ tapered design. As a result it comes in at 11.5” for the PCB (the same as the 5970), and with casing a full 12” long compared to the 5970’s 12.16”. This means that the 6990 has effectively the same space requirements as the 5970, cooling notwithstanding.

Meanwhile it’s the fan however that is going to catch the most attention and this is where we’re going to dovetail in to cooling. The 5970’s traditional blower had its strengths and weaknesses, the strengths being that blowers are relatively forgiving about a case’s ability to exhaust hot air, and the weaknesses being that the GPU (and VRMs) closest to the fan received better cooling than the farther GPU. The VRMs proved to be particularly problematic, as they could overheat well before the GPUs did and AMD does not spin up their fans based on VRM temperatures.

Correcting for this and at the same time allowing for even greater heat dissipation, the rear blower design is out. Its replacement is a design that we’ve seen in 3rd party cards before such as the Asus ARES 5870X2, but not in a reference design: a center-mounted fan/blower with a GPU to each side. The difference is critical and indeed cannot be understated: a rear blower channels most hot air outside of the case, while a center-mounted blower effectively splits the card in two, with one GPU + supporting chips being exhausted outside of the case, and the 2nd GPU + supporting chips being exhausted inside the case. The design is still enclosed, so everything goes out either the front or back of the card while fresh air is pulled in the center.

With the replacement of the blower, so has gone the heatsink. The 5970’s single large vapor chamber + heatsink design has been replaced in favor of a segmented heatsink, further driving home the concept that the 6990 is closer to 2 video cards sharing 1PCB than it is 2 GPUs on one card. Each heatsink in turn is connected to the GPU via its own vapor chamber, resulting in the GPUs being fully isolated from each other as far as cooling is concerned.

Even the thermal paste connecting the GPUs to the vapor chambers has been changed for the 6990 – AMD has replaced traditional paste with a phase change material. Phase change materials – pastes/pads of material that melt and solidify based on temperature are nothing new, however they’re still exotic; material similar to what AMD is using is not readily available as paste is. AMD even went so far as to suggest that reviewers not directly disassemble their 6990s as it would require a new application of phase change paste in order to achieve the same efficiency as the original material. The net result of all of this by AMD’s numbers is that the phase change material is 8% better than the regular paste they’ve been using.

Rounding out our focus on cooling is the VRMs, which have been relocated in order to correct for the 5970’s limited VRM cooling capabilities. The VRMs and controllers are now at the center of the board – now they’re cooled before the GPUs or RAM modules are. The profoundness of this is twofold: not only is it an improvement on the 5970, but with the 6990’s higher power consumption VRM cooling is even more important. As with the 6970, voltage regulation is supplied by Volterra MOSFETs and controllers.

All told, while the 5970 was designed to handle and dissipate 400W of heat, the 6990 is officially designed for 450W. In practice, at its limits in our test rig this is closer to 500W. To handle and dissipate that much heat in roughly 72in3 of space is nothing short of amazing.

Index Meet The 6990, Cont
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  • Ryan Smith - Tuesday, March 08, 2011 - link

    Yes, using the LateGameView benchmark. Like any other benchmark it's not a perfect representation of all scenarios, but generally speaking it's a reasonable recreation of a game many turns in with a large number of units. Reply
  • jabber - Tuesday, March 08, 2011 - link

    All cards at this level are niche. Very few of us have that much to splash on one component.

    I find it amusing that most of the folks here going "oh wow thats too noisy/power hungry/slow etc. so I wont be buying!", will just then load up Crysis on their 5770/GTX460 equipped PCs.

    Note to 95% of you reading this article...this card isnt/wasnt designed for you.
    Reply
  • araczynski - Tuesday, March 08, 2011 - link

    nice, but it sounds like the 6950CF owns the bang/$ award, this thing is too little for too much $/headache. Reply
  • araczynski - Tuesday, March 08, 2011 - link

    then again my 4850CF/E8500 system just played dragon age 2 demo at 1920x1200 with absolutely no problems, so have no reason to upgrade just yet, still. Reply
  • Gainward - Tuesday, March 08, 2011 - link

    I also just wanted to touch on that comment. Whilst these cards seem excessive to some you have to remember that @ this moment in time they are as I dub it the veyron moment like others in the past the concorde moment. They might not be for most people practical but to its like me saying to my team, look lets see what we can do. Not only that but having the crown of fastest single card (agreed single card but multi gpu) goes a long way to brand loyalty and advertising.
    An example I like to use is the GTX 560. Its a fantastic card and in many ways better… hang with me a second. In terms of actual raw power you get for sub £200 is incredible also factor in its quiet and wont eat through your electricity like a moth through primark. But…. to not produce these high end cards would be criminal. We need people to keep pushing as hard and fast (that sounds so wrong) at the the boundaries(agreed quite crudely in the 6990 case but hey I dont sit in either camp just wait a few days for the 590 for brute but crude).
    with the reduction in nm to 28 the power consumption and heat will be brought down further (dont need pointing out here that a lot of factors at play here it was just a generalisation) but sure we could see just as big and hot cards within practical reason.
    I would not say out of hand I would say its progress and with progress we can lear
    Reply
  • Figaro56 - Tuesday, March 08, 2011 - link

    Roger that. Reply
  • JimmiG - Tuesday, March 08, 2011 - link

    "Water cooled 6990s will be worth their weight in gold."

    They'll probably cost about that too...
    Reply
  • smigs22 - Tuesday, March 08, 2011 - link

    The r6990 stands out as a massive single card leader. The 6950CF offers far better price/perfomance with potential for 6970CF performance through BIOS flashing.

    Maybe you should break up some of the charts to show only single cards configurations (for those with motherboards lacking full/partial SLI/CF support).

    It will be interesting to see how enabled & what clocks the gf590 will arrive at, in order to keep its power-draw & temps down to reasonable levels??

    I wonder if someone would place a carbon tax on these bad boys....lol
    Reply
  • Figaro56 - Tuesday, March 08, 2011 - link

    The would have done this, but there is a cryo cooled case interior on the market yet. Reply
  • IceDread - Tuesday, March 08, 2011 - link

    If the card would have come with water cooling option or something like that, then it would have been a great product. Reply

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