Cooling the Antilles GPUs is a pair of large aluminum heatsinks made up of 37 fins each. The heatsinks are separated by a blower fan which is positioned in-between them rather than at the end of the card. This design is said to be more efficient as it will allow the fan to spin at a lower RPM yet provide the same amount of air across both heatsinks. The real key to this design is the use of vapor chambers and high endurance thermal compound. AMD has also provided adequate cooling for the card’s GDDR5 memory chips and VRMs using aluminum heatsink plates which span the length of the card, back and front. The vapor chamber design was first implemented in the Radeon HD 5970 and has already been used on other HD 6000 series graphics cards, however the HD 6990 features two of them. We are going to have to rely on photos from AMD to show you this. AMD claims the GPUs on the HD 6990 use a special kind of “phase change” thermal compound which improves thermal performance by 8% when compared to previous cards. Removing the heatsinks would basically bust this, or so we are told. For the most part the card’s fan operates quietly, helped by its impressively low 37-watt idle consumption. When gaming, the fan will inevitably spin up as the Radeon HD 6990 can consume a sweltering 375 watts under load, and then when pushed hard the card does begin to sound like a leaf blower. The heatsink and fan have been enclosed within a custom-built housing that conceals the entire graphics card, same as we saw on its predecessor. This setup helps protect the card very well; Nvidia has been using similar enclosures for some time as well on certain products. Removing the heatsink exposes the two GPUs, GDDR5 memory chips, and a few other critical components. With the heatsink off the Radeon HD 6990 looks considerably different than the HD 5970. The biggest change is the position of the GPUs, whereas the Radeon HD 5970 had them next to each other, they are now at opposite ends of the 12" long graphics card. The GDDR5 memory works at 5000MHz (1.25GHz x 4) on this particular model and features a 4GB capacity. This gives each GPU a theoretical memory bandwidth of 160GB/s thanks to the implementation of a 256-bit wide memory bus. Although the Radeon HD 6990 is not clocked as aggressively as the single-GPU HD 6970, with a core clock frequency of 830MHz it is still faster than the HD 6950. Simple math will tell you that because the Radeon HD 6990 is clocked roughly 6% lower than the HD 6970, it will be slightly slower than a pair of these graphics cards operating in Crossfire mode. The core configuration of the Radeon HD 6990 calls for 1536 SPUs, 96 TAUs (Texture Address Units), and 32 ROPs (Rasterization Operator Units) per GPU giving a total of 3072 SPUs, 192 TAUs, and 64 ROPs. A pair of 8-pin PCI Express power connectors are used to feed the graphics card enough power. This is the first time we’ve come across a reference board that requires a pair of 8-pin connectors. That said, the Crossfire equivalent would not only require two 8-pin power cables but also a pair of 6-pin connectors as well. The Radeon HD 6990 naturally supports CrossfireX, and therefore in the standard position we find a single connector for bridging two cards together. The only other connectors can be found on the I/O panel. Our review board featured a single dual-DVI connector along with an array of four Mini Display Port connections. With Eyefinity the HD 6990 can support a max resolution of 2560x1600 on six monitors, while standard cards can support up to five.
