HIS ATI Radeon HD 6990 Review. The Benchmarks.
A constructive comparison of the 6990’s performance should ideally feature its predecessor, the HD 5970, a pair of 6970’s to test in both single and crossfire configurations and Nvidia’s direct response to ATI’s latest creation, the dual GPU GTX 590. However, at the time of testing, the only other card at my disposal in the same performance bracket was a Zotac branded GTx 580, hence, this shall be our baseline reference.
We know that even AMD’s 5970 is able to edge out the GTX 580 in the majority of tests. Nevertheless, there remains a significant number of scenarios, including those mentioned at the beginning of this article, where either the tables are turned or the winning margin is very small. At the time of this analysis, the approximate price we can expect to pay for a GTX 580 is £390, while the 6990 will set us back around £100 more at £490, therefore, the 6990 will have to yield a 25% performance gain over its rival in order ensure a truly moral victory.
Crossfire vs SLI?
Scaling has consistently been something of a let down when it comes to dual GPU cards, the additional investment one makes to acquire a second card is rarely justified by the resulting performance gain. In our previous comparison, which pitted three GTX580s against two HD 5970s, we observed that the Nvidia cards were able to comfortably outscore their red rivals and moreover, that their advantage increased dramatically as soon as anisotropic filtering and anti-aliasing became part of the equation. While it’s true that the 580 emerged almost a year after the 5970 and would therefor have the benifit of extra time in development, the fact remains that the 5970, though still able set the standard when only a single card is used, does not scale nearly as well as the 580 when multiple cards are installed.
We have already discussed how the 5970’s “relative” memory limitations contribute to its lack of performance at high and eye-candy heavy resolutions but it is important to note that this does not entirely account for its poor scaling, nor has the issue been exclusive to ATI’s dual GPU cards. In fact every dual GPU card since Nvidia’s introductory 7900gx2 has, with the exception of a handful of games and benchmarks, scaled far worse in SLI and Crossfire than their single GPU counterparts:
NVidia:
9800gx2 (Dual GPU – 1024mb shared memory) vs. 8800gtx/8800gtx ultra/9800gtx/9800gtx+ (single GPU – 768mb/512mb dedicated memory).
The 9800gx2 yielded good results as a single card but was disappointing in SLI, even when compared to its one and a half year old predecessors.
Gtx 295 (dual GPU – 1792mb shared memory) vs. gtx 260/280/gtx 285 (single GPU – 896/1024mb dedicated memory).
One on one, the gtx 295 comprehensively outclassed the 260, 280 and 285, but soon as a second card was added – which one would expect to benefit the 295 even more – its advantage was significantly reduced. In TRI-SLI, the performance of three 280/285s displaced that of two 295s, despite each setup costing roughly the same.
ATI:
3870×2 (dual GPU – 1024mb shared memory) vs. 3870 (512mb dedicated memory)
4870×2 (dual GPU – 2048mb shared memory vs. 4870 (512/1024mb dedicated memory)
The last two generations of ATI’s flagship cards saw identical chips used on both the single and dual GPU models and unlike Nvidia, the same amount of memory allocated to each GPU. With one card, things panned out as expected. The performance of a single 3870×2/4870×2 was almost exactly double that of a 3870/4870. However, in both cases, adding a second card, yielded a pathetically small performance increase for the price. Despite constant promises of driver improvements for both quad SLI and quad crossfire. It would appear that, besides memory hindrances, the programming complications encountered when developing and refining drivers for 4 way GPU configurations also play their part in the underwhelming performance we have thus far witnessed from such setups.
To take the price vs performance debate to its logical extreme and establish whether or not the 6990s extra memory and ATI’s latest drivers have been able to break this long standing curse, I have decided to also include two further sets of results, one from a TRI SLI configuration made up of 3 GTX 580s and the other from a series of tests conducted on a dual 6990 setup. The cost of each package at the the time of writing is approximately £980 for a pair of ATI’s 6990, while three GTX 580s will burn a £1170 hole in the enthusiast’s pocket so this time, it is Nvidia that will need to justify £190 of additional investment by converting it to a performance gain of 20% or greater.