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Review: Nvidia GeForce GTX 660 Ti, Asus DirectCU II TOP, EVGA SuperClocked and AMD Radeon HD 7950 v2
by Damien Triolet
Published on October 25, 2012

Nvidia is continuing to roll out its Kepler architecture down the range with the arrival of the GeForce GTX 660 Ti. Very close to the GeForce GTX 670 in terms of spec, it could be well worth a look for gamers: we have tested the reference version as well as the customised Asus and EVGA models. AMD however intends to put a dampener on Nvidia’s party with updated specs for the Radeon HD 7950…

GK104 for everyone
In spite of what might have been expected, the GeForce GTX 660 Ti isn’t based on a new simplified version of the current high-end GPU. It uses the same GPU as the GeForce GTX 690, 680 and 670: the GK104. You can find all the details on this GPU in the review of the GeForce GTX 680. Ironically, with the GeForce GTX 660 Ti, this GPU is in fact probably now where it was intended to be in terms of its position in the range as it was not really designed as a traditional high-end GPU. With better performance than planned, less fierce competition than had been expected and the fact that the big GPU had been delayed or cancelled, Nvidia was however able to introduce the GK104 successfully for the high-end or even very high-end segment.

Little by little it has now been rolled out in the ‘Performance’ segment, which is the segment between the mid and high end and in which you generally find solutions that appeal to gamers looking for maximum performance at a reasonable price.

In designing the GeForce GTX 660 Ti, Nvidia has used a partially cut-down version of the GK104 that is very similar to the version used on the GeForce GTX 670: the number of processing units and the clocks are identical but the memory bus is at 192 rather than 256 bits, which allows Nvidia to drop its price to €300 (rather than €380) without affecting performance too much.

In spite of the 192-bit bus, Nvidia has retained a video memory of 2 GB for the main variant of the GeForce GTX 660 Ti, taking advantage of the fact that its GPUs support an asymmetric memory. How can this be? Two 64-bit memory controllers each address 512 MB while the third addresses 1 GB of memory. In other words this means that the GPU can access 1.5 GB at full speed on 192 bits and keep 512 MB in reserve with a slower 64-bit access. A 3 GB version with a symmetric memory configuration is also planned and will be offered by some partners.

The updated Radeon HD 7950
AMD apparently rushed to update the reference spec of the Radeon HD 7950, no doubt to respond to the GeForce GTX 660 Ti. The changes are similar to those introduced for the Radeon HD 7970 GHz Edition: the clocks have been revised upwards.

Here AMD has used PowerTune with Boost, a more precise update of its energy consumption technology which can now vary the voltage, which allows them to validate a higher GPU clock. While at the start the Radeon HD 7950 was clocked at 800 MHz, the new version is clocked at 925 MHz, with the higher voltage kicking in as of 850 MHz.

AMD says that all Radeon HD 7950 GPUs are compatible with this upgrade which can be implemented simply by updating the bios. Indeed we used a new bios supplied by AMD to test the solution here. This bios has however only been designed for the initial press samples of the Radeon HD 7950, the design of which is different to that of most cards available in stores. As this press model has a sturdier cooling system and power stage, it can handle this version’s higher TDP no problem: the TDP is up from 200 to 225W.

While in practice all the other Radeon HD 7950s should support the upgrade without any problems, with however a question mark over power stages which aren't cooled by a small radiator, it is up to each manufacturer to validate its own model (or not) and offer a new bios, either with an update for all cards or only for those manufactured as of now. Note that given how all AMD’s partners seem to have ignored the update of the specs of the Radeon HD 7700, we can’t be sure that they will all provide new bios’ for current HD 7950s, especially as it could complicate things for their overclocked models, on which it is harder to put an update into place.

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