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.

AMD has made a lot of its Eyefinity multiple-monitor technology in recent years; although the reliance on DisplayPort outputs and the resulting need for adaptors has probably slowed take up. Refreshingly, the HD 6990 is being bundled with a raft of adaptors to ease potential owners’ transition to triple-monitor gaming. These consist of passive and active mini DisplayPort to DVI adaptors plus a mini DisplayPort to HDMI adaptor. The DVI adaptors are only for Single-Link DVI, but you can still run three monitors up to 1,920×1,200. On the back of the card are four mini DisplayPort outputs; plus unusually a single Dual-Link DVI adaptor for those who want to run a single high-resolution (2,560×1,600) monitor.

We re-ran our tests on a three-monitor setup, such as the Samsung MD230X3 above, with our Full HD screens totalling a resolution of 5,760×1,080 pixels. Here we saw 74.2fps in Call of Duty 4 (below the usual 86fps maximum), 38.7fps in Crysis and 36.1fps in Stalker, all with 4x anti-aliasing enabled. This just goes to show that even with all its graphical might, the HD 6990 can be stretched by more extreme gaming setups.

Coming back to the card itself, one reason cited by AMD for the unusual arrangement of outputs is the need to get the maximum quantity of hot air out of the back of the card, something that a second DVI port would have restricted. The card has a single fan in the centre, which drives airflow over a pair of heat sinks on either side.

All that heat is a by-product of the card’s huge 450W potential appetite. In the main AMD has curbed its enthusiasm for power using its PowerTune technology to regulate the clock speed under extreme conditions and keep consumption down to a maximum 375W. That’s still a lot of juice, as the two 8-pin power connectors testify. You’ll need a very hefty power supply to get this card up and running smoothly. You’ll need a sizeable, uncluttered PC case as well with the card measuring a huge 303mm in length.

At £550 the HD 6990 is more than double the price of the HD 6970 – which currently costs around £270 inc VAT. Yes, it’s the most powerful graphics card we’ve ever tested, outdoing even Nvidia’s super-fast GTX 570 and 580 cards. However, even the most enthusiastic, die-hard gamers will surely balk at this card’s price, given the huge variations in its benchmark results. If every game ran as well as 3DMark 11 then we could see some justifying the expense, as it is, though we’d stick with the far-cheaper and more predictable HD 6970.