AMD Radeon HD 6990 4GB Review

AMD Radeon HD 6990 4GB Review

Manufacturer AMD
UK price (as reviewed) £539.99 (inc VAT)
US price (as reviewed) MSRP $699 (ex tax)

AMD Radeon HD 6990 4GB specifications

With this generation of high-end, single-GPU cards all on the table, consumers and manufacturers are still hankering for more: more power and more hardware bragging rights. Never mind the fact that Crysis 2 isn’t looking like a GPU-eating monster – larger monitors, higher resolutions and the increasing popularity of multi-monitor setups mean there’s never going to be a ceiling for GPU performance.

With the big single-GPU guns of the GeForce GTX 580 1.5GB and Radeon HD 6970 2GB already releases, the only way up for now is a multi-GPU card. While Nvidia has plans for a dual-GPU release in the near future, it’s AMD that got in first with its gargantuan Radeon HD 6990 4GB.


The HD 6990 4GB is a seriously huge card. Measuring 305mm (12in) in length, it’s actually the same length as its dual-GPU forebear, the Radeon HD 5970 2GB. However, it's larger in volume thanks to the typical black box casing that we’ve seen on other HD 6000-series cards. The HD 6990 4GB is also a little lighter than its predecessor, weighing in at 1,146g; 50g less than the HD 5970 2GB.

As with previous AMD dual-GPU cards, the basis for the card is two top-end GPUs – it uses the same Caymen XT GPUs found in (single-GPU) HD 6970 2GB cards. However, the two GPUs operate at lower frequencies than the HD 6970. With the HD 6990 4GB, this means the 3,072 stream processors run at 830MHz rather than 880MHz. Similarly, the 4GB of GDDR5 memory (2GB per GPU) is clocked at 1.25GHz (5GHz effective); roughly 9 per cent lower than the 1.375GHz (5.5.GHz effective) memory clock speed of the HD 6970 2GB.


By selecting such high-end, high-power GPUs, AMD has given itself a significant challenge when it comes to both powering and cooling this beast. As a result, it has had to investigate new technologies in order to make the HD 6990 4GB safe and reliable to use.

Most notably, the card breaks the PCI-E power specification, which states that no expansion card should consume more than 300W of power. The HD 6990 4GB in its factory configuration draws up to 375W of power; up to 75W from the motherboard, and 150W each from the two 8-pin PCI-E power connectors on the side of the card.


While this means that the HD 6990 4GB is effectively non-compliant with the PCI-E standard, AMD stated that breaking the 300W limit had always been ‘a matter of time,’ and that it was ‘not worried’ by any potential ramifications from PCI-SIG; the group that owns and manages PCI-E specifications and standards. Regardless of the result of breaking the PCI-E standard so brazenly, you’ll need a serious PSU to power the HD 6990 4GB, especially if you want to investigate its unique overclock mode.

AMD Radeon HD 6990 4GB specifications