AMD Radeon HD 6990 4GB Dual GPU Cayman Graphics Card
Antilles Architecture and Design
The AMD Radeon HD 6990 4GB card has been known by the media and even gamers since the first announcements from the Cayman launch last year but finally today we are able to discuss the technology behind it and the gaming performance it will provide users willing to shell out the $700 it will take to acquire. Stop in and see if your mortgage is worth this graphics card!
Graphics card that are this well endowed don't come along very often; the last was the Radeon HD 5970 from AMD back in November of 2009. In a world where power efficiency is touted as a key feature it has become almost a stigma to have an add-in card in your system that might pull 350-400 watts of power. Considering we were just writing about a complete AMD Fusion platform that used 34 watts IN TOTAL under load, it is an easy task to put killer gaming products like the HD 6990 in an unfair and unreasonable light.
But we aren't those people. Do most people need a $700, 400 watt graphics card? Nope. Do they want it though? Yup. And we are here to show it to you.
A new take on the dual-GPU design
Both AMD and NVIDIA have written this story before: take one of your top level GPUs and double them up on a single PCB or card design to plug into a single PCI Express slot and get maximum performance. CrossFire (or SLI) in a single slot - lots to like about that.
The current GPU lineup paints an interesting picture with the Fermi-based GTX 500 series from NVIDIA and the oddly segregated AMD HD 6800 and HD 6900 series of cards. Cayman, the redesigned architecture AMD released as the HD 6970 and HD 6950, brings a lot of changes to the Evergreen design used in previous cards. It has done fairly well in the market though it didn't improve the landscape for AMD discrete graphics as much as many had thought it would and NVIDIA's graphics chips have remained very relevant.
With the rumors swirling about a new dual-GPU option from AMD there was some discussion on whether it would be an HD 6800 / Evergreen based design or an HD 6900 / Cayman contraption. Let's just get that mystery out of the way:
The memory architecture runs a bit slower as well at 5.0 Gbps (versus the 5.5 Gbps on the HD 6970) but we are still getting a full 2GB per GPU for a grand-spanking-total of 4GB on this single card. Load power on the board is rated at "<375 watts" and just barely makes the budget for PCI Express based solutions with the provided dual 8-pin power connectors.
Memory speeds are overclockable as well from the 5.0 GHz default speed up to 6.0 GHz - and again, your mileage will vary.
When you move that BIOS switch on the HD 6990 from the standard setting to the overclocked setting, you aren't just changing the clock speed of the GPU but you are also changing the default settings for PowerTune. Instead of a target load power consumption of about 375 watts, the overclocked card will be able to target as high as 450 watts using some updated and improved circuitry on the board. It is worth nothing though that AMD is forced to make this 450 watt option an "overclocked" setting because it does exceeded the power draw of the PCI Express slot and associated connectors and would cause a fit for vendors attempt to selling systems using the HD 6990 to consumers. Enthusiasts that buy this card themselves though will have that option and we are glad that AMD continues to support readers like ours by enabling this type of thing.
Above you will see the digital programmable voltage regulators placed in the middle of the PCB, equidistant from either GPU, responsible for VDDC regulation, efficiency and the high current capacity of the card in its "unlocked" state. AMD claims that the symmetrical layout of the card will provide the most efficient power delivery to EACH of the two GPUs and associated memory so you don't have one chip able to run at 975 MHz while the other can only hit 950 MHz, for example. And you can bet that AMD is going to be putting only the very best of the Cayman GPUs on the HD 6990 in order to appease enthusiasts and to help keep that overall power consumption low(er).
The red line relates to the clock speed of the HD 6990 as we know it today and with the PowerTune technology implemented as we have discussed. The red arrows you see coming up from each game indicates the added performance a gamer gets out of this graphics card with the additional clock speed that it would not have been able to get if AMD removed the PowerTune settings. Now I realize that these results are from AMD and as such they might be a bit stingy with that the 570 MHz clock speed estimate without PowerTune - it IS in their interest to make us like and understand what it is doing. But even if the real-world speed is something like 650 MHz I think most users would easily take the ~150+ MHz of performance for the ability to run Furmark.
Obviously there is the downside that you will not be able to do the 6-panel Eyefinity configuration right away here - you can still do it, but you are going to need a DisplayPort 1.2 hub of some kind and good finding one of those.
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