With the upper hand over Nvidia for at least the past year, AMD (the ATI brand is no more) has taken the opportunity to do some rejigging for its HD 6000 series of cards. Rather than the expected next step upwards in speed and performance, they’re more like a redesign of what’s gone before, all in the name of value and efficiency.
The main change revolves around stream processors and, in particular, how they’re organised. While the HD 5800 cards employed a single complex processor that would delegate tasks to four slave shaders, the new Northern Islands family does away with slave processors entirely. Instead, AMD employs four complex processors which, while smaller in number, are capable of handling trickier tasks in less time.
The result is a very efficient architecture. As we’ve said, it’s not the top end – if you’re looking for enthusiast-level chips you’ll have to wait for the HD 6950 and HD 6970 in November. So, the specification is relatively modest: 1120 stream processors compared to 1600 in the HD 5870, and 1.7 billion transistors compared to its predecessor’s 2.1 billion. There’s a 900MHz core clock, one gigabyte of GDDR5 RAM running at 1050MHz and a 256-bit memory bandwidth.
Despite the cutbacks, the optimised stream processors still delivered impressive results. A score of 39fps in our 1920 x 1080 Very High quality benchmark is ten frames faster than 1GB Nvidia’s GTX 460 and just four frames short of the HD 5870, which cost more than $500 when it was released last year.
With 4x anti-aliasing activated, the HD 6870’s score of 34fps easily trumped the 25fps of the GTX 460, and the Radeon maintained a playable frame rate of 35fps at 2560 x 1600 and High quality. Only at Very High quality did the HD 6870 struggle, dropping to 25fps.
Nvidia’s GTX 460 took back ground in our 1920 x 1080 maximum quality DiRT 2 benchmark, although only by a couple of frames.
The HD 6870 performed well in our temperature and power tests. A peak temperature of 78 degrees is perfectly acceptable and sure to come down when board partners release cards with more efficient coolers, and our test rig’s peak power draw of 289W is broadly in line with the draw from the equivalent Nvidia’s cards.
At $315, whether it justifies the $70 price premium over the HD 6850 depends how much you need every ounce of power. The HD 6870 is certainly fast and efficient, but it can't match the older HD 5870 for raw speed. And for most people the savings make the HD 6850 a better-value choice.