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HD 3800 series makes good on R600 potential: a review of the AMD RV670

With the launch of its RV670 refresh, ATI has claimed dramatic improvements …


The R600 GPU architecture that AMD launched earlier this year hasn't proven itself to be a particularly bright feather in the company's cap. While the high-end 2900XT introduced some compelling new features such as custom filter anti-aliasing (CFAA), the card drew nearly as much power under load as an 8800GTX while providing the approximate performance of an 8800GTS.

Making matters worse, the 2900XT didn't offer the Universal Video Decoder (UVD) support that reviewers had generally assumed was standard across the entire R600-derived product line, and was significantly noisier than its G80 competitors. The combination of these factors wasn't enough to completely torpedo the 2900XT's market appeal, but the card was a poor flagship product and a tepid offering.

The R670 redesign that AMD/ATI has launched is meant to both fix the various flaws in the R600 and position the company more competitively against NVIDIA. The new HD 3800 series has arrived on the market promising dramatically reduced power consumption, lower thermals, and better scaling over the long term. The two points we'll focus on in our first look at the new GPU are whether AMD/ATI has delivered a compelling refresh of the R600 series, and how well that refresh compares to NVIDIA's newly-launched 8800GT on a representative selection of games.

Note that we'll be following up this review with a series of benchmarks of the RV670 to be posted on Kit, the Ars Technica hardware and gadgets journal. So the present article is just start of our ongoing investigation of the RV670, and we've chosen to focus it on this card as mid-range gaming that might actually go into a reader's build. So you won't see benchmarks at every possible screen resolution and quality setting. Rather, the point is to get a realistic, straightforward, gamer's-eye view of how AMD/ATI's new GPU stacks up to its predecessor and to its closest competition.

Power management and HD playback

Two new features that are debuting in the HD 3800 series are its additional power management capabilities (PowerPlay), and a new version of ATI's UVD technology, UVD+. ATI's UVD+ technology provides HD decoder support in hardware, reducing the amount of CPU time required to maintain smooth playback. Its presence in both the 3870 and 3850 models is signficant, as the original 2900XT didn't support UVD functionality. 

PowerPlay is ATI's code name for its next-generation power management technology. It's available on both the HD 3850 and the 3870, though it'll undoubtedly be more popular with laptop owners wanting to eliminate any unnecessary use of power. PowerPlay will debut with the Mobility Radeon HD 2000 series of video solutions. GPUs, like CPUs, have gradually incorporated increasingly sophisticated power management capabilities. In that sense, PowerPlay is more an evolution than a brand-new technology, but it supports several new capabilities to reduce laptop power consumption.

PowerPlay has the ability to dynamically control both the clock speed and the voltage of the video card in hardware, rather than requiring a software solution. According to AMD/ATI, integrating these functions at the hardware level allows the video card to adjust its performance profile much more quickly than a software solution would, thereby extending battery life.

The other new trick up AMD/ATI's sleeve is the Radeon HD 2000 series' support for dynamic back-bias voltage control. As die geometries shrink, electrical leakage becomes a more serious problem, and can cause chips built on a smaller process to leak more energy than their predecessors (e.g., Prescott). AMD's solution to this problem is to increase the threshold voltage of the transistors in question, thus cutting off sub-threshold leakage.

As for software integration, ATI guarantees that the PowerPlay control panel and Vista's power management software will always remain synchronized; allowing users to activate whatever power/performance profile best fits their needs from either location.

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