Radeon HD 6990 4GB Specifications
With two full-fat Caymen XT GPUs, the total number of stream processors inside this 12in-long card is a staggering 3,072. However, these run at 830MHz rather than the 880MHz of a single-GPU HD 6970 2GB. This has resulted in a horrifically high maximum power draw for the card of 375W – you’ll need a hefty PSU to handle this power-hungry card and still be able to run the rest of your PC.
As the GPUs are just the same as the Caymen XT GPUs used in the HD 6970 2GB, each has a 256-bit memory interface and the same 32 ROPs, two tessellation units and two rasterisers. As the memory of the HD 6990 4GB runs slightly slower than that of the HD 6970 2GB, however, the memory bandwidth for each GPU is slightly less at 160GB/sec rather than 176GB/sec.
However, the HD 6990 4GB has a dastardly trick up its sleeve in the form of the Antilles Unlocking Switch
, which overclocks each GPU by 50MHz and overvolts them to keep this stable. While this overclock is a standard feature of all HD 6990 4GB cards, it will void your warranty and also boost the power consumption of the card to an incredible 450W. As such, you should only use this switch if you have a high-wattage, high-quality PSU – the card alone will nom through 31.25A of current.
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Aside from its extreme power consumption and AMD's efforts to tame the heat - using a vapour chamber cooler for each GPU as well as some exotic TIM - the HD 6990 4GB also boasts a super-sized selection of connections. As well as solitary CrossFire connector enabling four-GPU CrossFire craziness, the card also offers a dual-link DVI port and four mini-DisplayPort 1.2 ports.
Worry not though, Eyefinity users, because AMD is shipping a passive connector to convert one mini-DP output into a single-link DVI connection, plus an active alternative and a passive mini-DP to HDMI convertor. That should ensure Eyefinity support for any screen setup. It’s certainly good to see that easy Eyefinity support is high on AMD’s priority list with this graphics card, as triple-screen gaming can be excellent.
| ||AMD Radeon HD 6990 4GB||AMD Radeon HD 6970 2GB||AMD Radeon HD 6950 2GB||Nvidia GeForce GTX 570 1.5GB||Nvidia GeForce GTX 570 1.3GB|
|Codename||Antilles||Cayman XT||Cayman Pro||GF110||GF110|
|Stream Processors||2 x 1,536 (830MHz)||1,536 (880MHz)||1,408 (800MHz)||512 (1,544MHz)||480 (1,464MHz)|
|Layout||2 x 24 SIMD Engines||24 SIMD Engines||22 SIMD Engines||16 SMs, 4 GPCs||15 SMs, 4 GPCs|
|Rasterisers||2 x 2||2||2||4||4|
|Tesselation Units||2 x 2||2||2||16||15|
|Texture Units||2 x 96||96||88||60||60|
|ROPs||2 x 32||32||32||48||40|
|Transistors||2 x 2.6bn||3.6bn||2.6bn||3bn||3bn|
|Size||2 x 389mm²||389mm²||389mm²||520mm²||520mm²|
|Amount||2 x 2GB GDDR5||2GB GDDR5||2GB GDDR5||1.5GB GDDR5||1,280MB GDDR5|
|Frequency||1.25GHz (5GHz effective)||1.375GHz (5.5GHz effective)||1.25GHz (5GHz effective)||1.02GHz (4.08GHz effective)||950MHz (3.8GHz effective)|
|Bandwidth||2 x 160GB/sec||176GB/sec||160GB/sec||192.4GB/sec||152GB/sec|
|Power Connectors||2 x 8-pin PCI-E||1 x 6-pin, 1 x 8-pin||2 x 6-pin PCI-E||1 x 6-pin, 1 x 8-pin PCI-E||2 x 6-pin PCI-E|
|Maximum Power Draw||375W||250W||225W||244W||219W|
|Idle Power Draw||37W||Not Specified||Not Specified||Not Specified||Not Specified|
|Recommended PSU||Not Specified||Not Specified||Not Specified||550W||550W|
|Typical Street Price||£530-£550||£270||£220||£400||£300|