A Closer Look
AMD is using a big and complex heatsink which cools all components at the same time: GPU 1, GPU 2, memory of both GPUs, voltage regulation circuitry and the PCI-Express bridge chip. AMD claims to use a special "phase change" thermal interface material, and they say once removed you will not be able to get the same temperatures with your own TIM. If you take a close look at the second picture you can see that the paste is not liquid, but more like brittle wax.
This little switch is present on the HD 6950 and HD 6970 cards, too. Originally it was designed as a backup feature, so you have a second BIOS in case you manage to destroy your main BIOS.
AMD has changed the behaviour on the HD 6990 and turned it into an overclocking feature. When left in the default position, the card uses the normal settings of 830 MHz core and 1.12 V GPU voltage. When set to the second position, the card will use a BIOS that's clocked at 880 MHz core and 1.175 V. The switch is covered by a scary big, yellow sticker which basically tells you that switching the BIOS will void your warranty.
During production AMD does a "bootup" test at the overclocked settings, but they do not guarantee stability of the card in this mode. The sticker itself did not pose a big problem, it can be removed, moved and put back easily.
The backplate is made from metal and serves to protect the components on the back from damage. It also helps with cooling the memory chips and acts as a general heatspreader. Warning: This plate gets quite hot when the card is heavily loaded. I moved the yellow sticker from the switch to the middle of the backplate where it's hard to lose, still visible and out of the way.
The card requires two 8-pin PCI-Express power connectors. Together with the PCI-Express x16 slot this configuration is good for 375 W of power - AMD says their board can draw up to 375 W in "normal" mode and up to 450 W when overclocked.
The GDDR5 memory chips are made by Hynix, and carry the model number H5GQ2H24MFR-T2C. They are specified to run at 1250 MHz (5000 MHz GDDR5 effective).
AMD is using two Volterra's VT1556 voltage controllers on their HD 6990 (one for each GPU). The VT1556 is also present on the reference designs for HD 6950 and HD 6970.
The PCI-Express bridge chip which connects the two GPUs and interfaces with the system via PCI-Express 2.0 is made by PLX. Apparently PLX lets ATI rebrand their product. According to AMD the bridge chip supports PCI-Express 2.1 x16 which supplies enough bandwidth to both GPUs for any situation. This is the same bridge chip as used on the Radeon HD 5970.
AMD's new Cayman graphics processor is made on a 40 nm process at TSMC Taiwan. It uses approximately 2.64 billion transistors on a die area of 389 mm².