AMD Radeon HD 6990 review

AMD’s 6-series cards have generally impressed us. The most powerful graphics card to date was the AMD Radeon HD 6970, which we gave our Ultimate award but noted that the vast majority of gamers would be better off with the almost as powerful HD 6950. Based upon its name, you’d be forgiven for thinking that this HD 6990 was merely a slightly faster iteration of those two cards, but instead AMD has squeezed two GPUs into the one card.

We’ve seen this practice before on the HD 4870 X2 and the HD 5970. We liked the X2 moniker, it made it very clear what you were getting, rather than simply badging the card as the next step up -when really it’s in an entirely different league. This isn’t just a matter of performance, dual-GPU cards have far higher power draws and often suffer from compatibility issues with games. Such a card will never achieve double the performance of a single GPU card, though, so maybe AMD should be applauded for avoiding this suggestion with X2.

The HD 6990 consists of two HD 6970 Cayman GPU cores, these are fully-fledged with no cuts or revisions, giving the card a staggering 192 texture units with 3,072 stream processors. It comes equipped with 4GB of GDDR5 memory, 2GB for each GPU. This runs at 1,250MHz, equivalent to the speed of the HD 6950’s memory, rather than the 1,375MHz of the HD 6970. The architecture may be doubled-up but stock clock speeds have been dropped from 880MHz to 830MHz, placing the HD 5990 nearer the 800MHz HD 6950 in this regard.

That said there is a simple option to overclock the GPUs back to full HD 6970 speeds. As with previous 6900 cards, this one has a dual BIOS – with a selector switch on the side. The original idea was that advanced users, who might want to flash the BIOS to tweak or update their cards, would have a fall back should the new settings prove unusable. With this card, AMD has preloaded the second BIOS slot with an overclocked version, with raised voltages to support the switch up to 880MHz, although this change doesn’t affect the memory speed.

Our initial tests provided us with mixed results when compared to the HD 6970. For example, in Crysis, we saw a modest increase in the average frame rate from 41.9fps to 45.6fps – at 1,920×1,080, Very High detail and 4x anti-aliasing. However, running the same test at the more forgiving High detail settings, the HD 6990 actually came out slower than its single-core counterpart by about 10fps. Now these are very early drivers, in fact AMD only provided us with the driver for testing a couple of days before the card’s release. Using the faster BIOS setting, made no appreciable difference in our test.

Other tests showed far more positive signs of where your £550 is being spent. Our DirectX 11 Stalker test leaped from 56.3fps on the HD 6970 to 77.1fps here, a noticeable improvement. The new 3DMark 11 benchmark suite was very appreciative of the HD 6990’s raw power, with the final score almost doubling the HD 6970’s 1,854, with a massive 3,375. This illustrates perfectly that it’s not the HD 6990’s graphical prowess that is in question, but whether your software is able to make the most of it.