Review: AMD runs rings around NVIDIA with its 6990, holding on to the fastest video card in the world tag for another generation.
Once upon a time AMD would have led this generation of hardware with the launch of the RADEON HD 6990. This is its flagship card, a dual-GPU beast formerly codenamed Antilles that we have been waiting for forever since the rollout of the 6000 series began. It’s the first graphics card capable of knocking over the previous generation 5970, which held the crown of fastest card since its launch in late 2009.
The 6990 ships with both GPUs clocked at 830MHz and memory at 1250Mhz. AMD has opted for a total of 4GB of GDDR 5 on the 6990, arranged in 2GB chunks that connect via a 256-bit memory bus. One unique thing about the 6990 is that AMD has included twin BIOSes on these cards. Flick a small switch on the top of the card and the card automatically overclocks, cranking the core speed up to 880MHz and the voltage from 1.12V to 1.175V. It also voids your warranty, although with the efforts put into power regulation on the 6000 series we wouldn’t expect this simple switch to fry the card.
Much like NVIDIA has based its dual GPU GeForce GTX 590 around two GF110 chips, AMD has employed a couple of Cayman GPUs on this card. These are effectively downclocked RADEON HD 6970 GPUs, each with 1536 shaders. These GPUs use the updated VLIW 4 shaders that replaced the VLIW 5 ones used last generation. They sit alongside newer generation tesselators that have closed the gap with NVIDIA’s Fermi architecture, and are paired with new power management chips designed to clamp GPU performance to TDP. This means that performance drops when a program like Furmark puts unrealistic strain on the GPU.
The downside of using such powerful GPUs is that the card draws around 375W in normal mode, and 450W with the overclock switch flicked. Because of this you’ll need a serious PSU with twin 8-pin PCI-Express connectors.
As is often the way with ultra high-end graphics cards all of the products out there at the time of writing used AMD’s reference heatsink design. This is an evolution of the blocky vapour-chamber-based coolers used on the rest of the 6000 series, but this time it has two vapour chambers, one for each GPU. The fan sits in the centre of the 30cm long card, pushing air over both cores. This means that while it’s exhausting air from one out of the rear of the case, the other is venting inside. This is a similar design to that used by NVIDIA on the GTX 590, and means that you’ll need to put some thought into extra cooling if you are using one (or two) of these monsters.
Display outputs are well worth mentioning too. The 6990 continues AMD’s trend of packingthe cards with DisplayPort outputs. There is a sole DVI port on the card, with four mini-Displayport connections as well. Thankfully AMD ships the somewhat esoteric and expensive adaptors that you need to run three DVI displays. Anymore than three and you’ll need to be using Displayport monitors.
We were fortunate enough to get our hands on two RADEON HD 6990 cards for our testing, so we haven’t just looked at single card performance. AMD has been going great guns with its Crossfire scaling of late, especially compared to the relatively poor scaling of NVIDIA’s cards in SLI.
Our testing was done using a Core i7 2600K, 4GB DDR3 and an ASUS ROG Maximus IV Extreme motherboard. We used an Antec 1200W PSU in order to supply enough juice to run two 450W cards as well as the rest of the system. We ran through the standard array of Atomic benchmarks, however due to time constraints we weren’t able to overclock beyond the basic switch method. We have compared the results to NVIDIA’s GeForce GTX 590, which is the main competitor to AMD’s flagship.
Issue: 137 | June, 2012