AMD Radeon HD 6990 "Antilles" Video Card Review

The Radeon HD 6990 is being launched today, and we have full coverage of specifications and our gameplay experiences compared to several high-end dual-GPU solutions out there. If you are looking for a single video card package that packs a punch and provides headroom for hardware enthusiasts, this is a solid solution.


We are finally able to reveal our gameplay experiences, performance numbers, and specifications of the new Radeon HD 6990 video card from AMD. On February 26th, 2011 we shared with you our first gameplay experiences using this new video card in a game demo. While we did not share performance numbers, we hinted at a high level of gameplay experience and performance surpassing a single Radeon HD 6970. A few days later we showed a few pictures of the video card, revealing some of the features. We are going to talk about this new high-end video card from AMD and then do some gameplay testing in comparison to three other multi-GPU setups that are competing for your money.

First, let's reveal the price as this is likely the most important factor in your buying decision. The new AMD Radeon HD 6990 is going to set you back $699 MSRP. This is no cheap video card! You are in essence purchasing two Radeon HD 6970 GPU based video cards in one single video card package.

AMD Radeon HD 6990

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The Radeon HD 6990 is made up of two Cayman XT ASICs, in essence, two Radeon HD 6970 GPUs are on the PCB. AMD likes to combine specifications when talking about one video card package such as this, so that is why you will see it listed as having 3072 ALUs, 192 Texture Units and 64 ROPs. In reality, each GPU has 1536 ALUs, 96 Texture Units, and 32 ROPs, just like a Radeon HD 6970 GPU. The architecture remains exactly the same on each GPU as they are indeed Cayman XT ASICs which are screened to be high quality parts for this video card. The clocks are a different story, but maybe not for the reason you are thinking....

The clock speeds of the cores and the memory have been decreased from 6970 specs. The core clock speed runs at 830MHz versus 880MHz on a single Radeon HD 6970 video card. Therefore, combined, that is a 100MHz difference in GPU frequency. The memory consists of 2GB of GDDR5 per GPU on a 256-bit memory bus. This is exactly the same as a Radeon HD 6970 video card, except for the frequency. A Radeon HD 6970 has its memory running at 5.5GHz while on the Radeon HD 6990 the memory will be running at 5GHz. This is indeed "CrossFireX" on a card.

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What you end up with is basically two down-clocked Radeon HD 6970's in a single video card. The reason that the core frequency and memory frequency has been lowered is not because of thermals, but because AMD wanted to keep the default configuration of this video card within the PCIe specifications of 375 Watts or lower. The graphics card itself is in fact engineered to be a 450 Watt capable video card! That means the hardware, the thermal solution, all of it, is rated up to a 450 Watt load capacity. The default configuration of this video card has a lot of headroom.

AMD is using new digital programmable Volterra regulators in this design. AMD has moved the regulators to the center of the board design to help provide efficient power to each GPU and its memory. Note that the PLX bridge chip providing the PCIe lanes between both GPUs is the same one used on the Radeon HD 5970, there have been no changes there. The thermal solution has been upgraded on the Radeon HD 6990 and uses a new kind of thermal phase change pad that transfers heat between the GPU and the heatsink. Both GPUs have a large vapor chambered heatsink atop them completely independent. There is a central fan and a shrouded design. Again, AMD has built this thermal solution to handle 450 Watt load.

Extreme Overclocking

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AMD has not forgotten the enthusiast gamer with this video card. The only reason the Radeon HD 6990 ships with a default clock speed of 830MHz and memory at 5GHz is to keep the video card within PCIe specifications. The GPUs operate at a lower Voltage in this shipping clock speed. What AMD has done is to use the dual-BIOS feature on board to give you more performance and better chances at overclocking.

The BIOS switch atop the video card ships in the #2 position. There will be a yellow caution label over this switch so you do not unknowingly change its position. This position gives you 1.12V of GPU power and operates at the 830MHz frequency. This position is read-only so you cannot overwrite the default BIOS. The fun really begins when you switch this video card into the #1 BIOS position. Doing so turns the Voltage up on each GPU to 1.175V and raises the core frequency of each GPU to 880MHz! At 880MHz you are matching the clock speed of the Radeon HD 6970. The memory however, is not changed.

This extra voltage on the GPU also gives you the ability to overclock the GPUs even higher than you would at the default #2 BIOS position. AMD says we should be able to get 900+ MHz frequencies out of these GPUs using the higher Voltage position. Of course, moving the slider to #1 will increase the board power and push this video card outside the PCIe spec. That is why AMD did not ship at these speeds.

It will be interesting to see how high you can overclock in the #2 position at first, with the lower Voltages, and then how high you can go in the #1 position with the higher Voltages. Also note that the #1 position is writeable, so you can write your own BIOS to this position and have the video cards frequencies set by the BIOS. If you mess it up all you have to do is switch to the #2 position for the card defaults and then reload your BIOS.

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AMD has fitted this video card with an array of display options. Firstly, they have utilized one entire row of the backplane to the cooling vents to exhaust air. AMD could have shortened these vents to allow more display options, but then the video card would not have had the cooling it needed. The bottom row on the backplane has one DVI port and four mini-DisplayPort connectors of the 1.2 version. If that one DVI port scares you, don't let it. AMD told us that in every retail boxed Radeon HD 6990 video card package you will get three adapters.

You will get adapters that convert the miniDP signal to a single-link DVI connector. That is the catch though, it is only single-link, meaning you won't be able to run a 30" 2560x1600 display off of this adapter. However, you can still run that display off of the onboard dual-link DVI port on the video card. You will also get a miniDP to HDMI adapter. If you are getting a Radeon HD 6990, and you have more than one display, it seems you might want to look for displays that support DisplayPort.

AMD Radeon HD 6990 Pictures

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These "naked" pictures of the Radeon HD 6990 were provided by AMD so you could see what's underneath the hood. The new thermal application used is such that if we took apart the video card, we'd never get the same thermals out of it again, so it would be rather hard to take apart and put together, until we get the proper specification TIM. This video card is not like the Radeon HD 6970, its construction is different.

Underneath you can see the two GPUs spread far apart, the power circuitry centered and the PLX chip off-center. The heatsink plate is quite "simple" with just two vapor chamber heatsinks atop the GPUs and a center fan.

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The way the cooling is setup hot air will exhaust out both the backplane of the video card as well as the front of the video towards the front of your case. The center fan draws in air and pushes that air out both ends of the video cards. Therefore, if you have front case fans at video card level pulling air in, that air will directly hit the hot air pushing out. You might want to position your fans above or below the video card so the two air streams don't hit each other. Also, be careful of installing a video card right up against this video card. If you do so, you will cut off the air intake from the fan, and that would be bad news. It is recommended that you leave a slot empty between this video card and another.

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The Radeon HD 6990 requires two 8-pin power connectors for operation, but the video card will still operate at 375W max board power to keep within PCIe spec. We have three Displays hooked up here for Eyefinity and we had no issues getting it to work. In fact with the new Catalyst control center it only took a few seconds to enable Eyefinity and arrange it. The AMD Radeon HD 6990 measures 12 inches, yes this video card is a foot long, make sure you have plenty of space in your case to install it.