When AMD launched its ‘Northern Island’ series of GPUs, first with the HD6870 and HD6850 cores (code-named ‘Bart’), and more recently the ‘Cayman’ cores (HD6970 and HD6950), the one everyone really wanted to see was the dual-cored flagship Antilles, now released as the Radeon HD6990. With the wait over, we leapt at the chance to take a look at the fastest GPU on the planet, in the shape of this card from AMD stalwart Sapphire.
Inside the beast
At the heart of the HD6990 are two GPUs sitting on a large PCB. Did we say large? This thing measures a staggering 305mm (12in), in length and weighs in at an impressive 1.14kg – so unless you’re the owner of a huge tower case, this won’t be the card for you no matter how deep your pockets are.
The two GPUs in question are a pair of high-end Cayman XTs, as found on the HD6790 cards but with slightly lower core and stream processor (all 3072 of them) clock speeds than the standard XTs – 830MHz, compared to the usual 880MHz. Also running slower is the memory clock; the 4GB of GDDR5 (running through a 256-bit bus) is clocked at 1,250MHz (5GHz effective) instead of 1,375MHz (5.5GHz effective).
As with other recent Northern Island-based cards, the Sapphire has a BIOS switch, but on the HD6990 it works differently from those of earlier releases. In the default position 1, it supports the factory clock settings for the core of 830MHz at 1.12 volts. Switching to the position 2 provides an increase in the core clock speed to 880MHz, with an increase in the voltage to 1.175 volts.
So far, so good – but the fly in the ointment is that grey area concerning the voiding of the product warranty by overclocking even when the overclocking is done via a manufacturer fitted switch, so it may be best to play safe and leave the switch alone considering how much this thing costs.
Feeding the beast
On top of the card there is two 8-pin PCI-E power connectors. Yes this card takes some powering up, as you might imagine with two top-end cores inside it – especially if you choose to ignore the warnings and use the BIOS switch to run it at 880MHz.
From the ground up ,the HD6990 has been designed to consume a whopping 450 Watts of power in its overclocked state. Even running at the stock speeds, it still requires 375 Watts – so you’d better make sure your power supply is up to the job. All this power means one thing – heat, which leads us on to the cooling.
Noisy or what?!
Keeping all this lot cool is a tough challenge, and AMD has taken the it’s for gamers, so it doesn’t matter how loud the fan is route with its reference cooler design. When the going gets tough, the fan spins up and makes an almighty racket. It’s the loudest graphics card we have heard for quite some time.
Sapphire has used AMD’s reference design, the only difference between that and the cooler on this card being the sticker on the front. It will be interesting to see if, further down the road, the company tries to keep the HD6990 both cool and quiet with one of its own designs of cooler.
Out the back
The HD 6990 has an unusual set of outputs on the I/O plate, in as much as there’s only a single DVI port. The other four outputs are mini-DisplayPorts, but Sapphire has bundled enough dongles and cables with the card to cater for just about any eventuality: passive mini-DP-to-DP cable, passive mini-DP-to-SL-DVI and mini-DP-to-HDMI dongles. There’s also an active DP-to-SL-DVI dongle, as well as the usual DVI-to-VGA adaptor and a CrossFire bridge cable. In Eyefinity mode, the HD6990 can currently support up to five screens; however, when the DisplayPort 1.2 drivers eventually surface you’ll be able to daisy-chain additional DisplayPort 1.2 monitors to each DP output.
So is it fast, then?
Simple answer: yes, very. In fact, it’s very hard to find a game or benchmark that the HD6990 doesn’t make mincemeat of – even at very high resolutions.
Running Crysis Warhead at a 3840×1200 resolution with 4x Anti-Aliasing and 4x Anisotropic filtering with all the in-game detail levels at their highest settings, the card still managed to produce an average frame rate of 50fps. In DiRT 2 at the same resolution, it produced an average of 102fps.
Needless to say it’s the fastest card we’ve ever tested, with Futuremark’s latest 3DMark11 benchmark giving it a score of 8727 in the performance test.