AMD's dual GPU cards have come a long way in the past several years. The original Radeon HD 3870 was noisy, ran hot and didn't always perform up to snuff. Since then, AMD's Catalyst Driver suite has substantially improved the performance and breadth of CrossFire-supported games.
On the hardware side, AMD is pulling out all the stops with its Radeon HD 6990 card. The company understands that a dual GPU card is most appealing to a small band of enthusiasts who really want the card to push the edge of the envelope, both in terms of engineering and features.
Despite being fully 12 inches long - like its predecessor, the Radeon HD 5970-the HD 6990 looks a little less imposing than the 5970. Maybe it's the center-mounted fan, which visually breaks up the huge mass of the cooling shroud.
The Radeon HD 6990 combines twin Cayman GPUs, 4GB of GDDR5 and a new cooling system.
Still, it's a big, heavy card that will only fit in larger PC cases, so make sure your case has the room for it.
The HD 6990 is essentially two Radeon HD 6970 cards built onto one card. While the base core clock speed is down a bit, at 830MHz, the full 6970 has been replicated, complete with 3,072 total shader ALUs, 192 texture units and 4GB of GDDR5 running at 1250MHz.
A pair of HD 6970 GPUs and all that GDDR5, even with the core clocks cranked back to 830MHz, consumes serious power; the HD 6990 ships with two 8-pin PCI Express power connectors. Also built into the card is a tiny physical dip switch that allows you to overclock and overvolt the core clock with a single flick, to 880MHz. Flicking that switch turns the 6990 into full, screaming dual HD 6970s, but at a hefty power cost. At full throttle, the overclocked HD 5990 used 528W - more power than we've ever seen from a single graphics card. The card itself, when overclocked, consumes up to 450W, which requires serious voltage regulation. AMD touts its use of Volterra digital programmable regulators and cherry-picked GPUs which would run at high voltages and clock speeds without melting.
The dual Volterra digital regulators are the rectangular chips at the top. The two GPUs are symmetrically laid out.
Cooling dual Cayman GPUs and 4GB of video RAM takes a serious cooling system. AMD re-engineered the cooling system, incorporating a full-board heat dissipation system with dual vapor chambers.
The heat sink fins each cover a separate vapor chamber located above each GPU. The copper head sink is thermally linked via phase change thermal interface materials.
The central fan pulls heat from the rearmost GPU, pushing that air over the front GPU. Since all the video connectors are mounted on one side of the double-wide PCI bracket, the other bracket side becomes a full-height exhaust vent.
The HD 6990 ships with five video connectors built in, one dual-link DVI connector and four mini-DisplayPort 1.2 attach points. Retail boxes will ship with three additional adaptors, one miniDP to single link DVI passive, one miniDP to single link DVI active and a miniDP to HDMI passive.
Four mini-DP 1.2 ports plus a dual link DVI connector enable full Eyefinity support.
So the Radeon HD 6990 seems well engineered. How does it actually perform? We cranked up the standard testbed, loaded up the benchmarks and took it for a spin. We compared the HD 6990 (with the OC switch in both settings) to an overclocked eVGA GTX 580 SC, and the previous generation Radeon HD 5970.
Any lingering doubts as to who is the new performance champ are now gone. In games that are seem mostly bandwidth or texture bound, we see little difference between the OC setting and the standard setting. It's worth noting that we did see games crash on a couple of occasions when the card's switch was set in the OC setting, while the 6990 was completely stable at the standard setting.
So for the moment, AMD gets to hoist the PC graphics performance crown onto its brow. But fame and GPU fortune can be fleeting, and already rumblings of a dual GPU Nvidia-based card have hit the Internet rumour mills.
Will you want one? At $US699, the price is pretty steep, especially if you consider that a single Radeon HD 6970 costs about $US360. Also, it's a big card, so make sure you case has room for a foot-long card. And you'll need a robust power supply to deliver all that juice.
Nevertheless, the temptation is there – that's a lot of raw GPU power on a single card. The price of GPU glory is never a small one.
$US699 (est) http://www.amd.com
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