First planned for December, then January, then February, the new captain of the AMD fleet was finally released at the beginning of March. The reason for these delays lies in the complexity of the production of what is a monster card, using two Cayman GPUs, similar to those that equip the Radeon HD 6970. The goal is clear: to replace the Radeon HD 5970 at the same time as underlining AMD’s lead over the GeForce GTX 580 and getting ready to face down the GeForce GTX 590.
Bi-GPU: now a tradition
Since the Radeon HD 3000 generation, a bi-GPU flagship product has been released with each new graphics card range: Radeon HD 3870 X2, Radeon HD 4870 X2, Radeon HD 5970 and now the Radeon HD 6990. Most of these cards have allowed AMD to gain an advantage over NVIDIA, who, by designing enormous GPUs, has found it harder to develop bi-GPU versons and must often fall back on a die-shrink for a lower energy consumption revision before creating its bi-GPU cards.
With Cayman, our test for which you can find here
, AMD has however aimed higher than usual. While the results in terms of pure performance are mixed, power consumption is going up. In spite of this, AMD persisted in the idea that a bi-GPU version remained on the agenda, codename Antilles, with the PowerTune technology to manage energy consumption levels.
To recap, PowerTune uses numerous sensors placed on each GPU block to monitor the activity levels of the GPU and then estimates energy consumption levels according to what is expected for particular activity levels. Given that there can be significant variations from one sample to another of the same GPU, AMD has based its energy consumption to activity levels predictions according to worst case, namely GPUs that suffer from high current leakage and run at a high temperature. Depending on the sample used, real energy consumption may therefore be similar or lower, sometimes by a lot, to that estimated by the GPU, which cannot measure real energy consumption.
At the same time, AMD sets an energy consumption limit for the GPU. Once this limit is exceeded, the GPU gradually reduces its clock and then increases it again when energy consumption drops. The GPU can thus adapt its clock to respect a given thermal envelope in real time.
We thought that AMD would use PowerTune to market a solution that would offer the best possible performance within a thermal envelope of 300W, the maximum as defined by the PCI Express 2.0 standard. In fact, AMD has gone beyond this limit, probably to give the card higher performance levels than the Radeon HD 5970, which is based on GPUs with a slightly better power efficiency. You can therefore choose to limit your Radeon HD 6990 to either 375W or 450W! This is a record and the subject of a fair amount of discussion as a result, especially as it is not clear what AMD’s guarantee covers the card for…