AMD shipped its first DirectX 11 GPU, the Radeon HD 5870, in late 2009. Despite supporting Microsoft’s latest 3D API, the new GPU was built on an architectural foundation based on the earlier Radeon HD 4000 series. AMD is now launching its second-generation DX11 product, code-named Northern Islands, but these new processors are based on an architecture that’s a from-the-ground-up new design.
The company also approaching this launch a little differently: Instead of pushing out a new, high-end product, AMD is launching two GPUs—collectively code-named Barts—that will be aimed squarely at the midrange market, where cards sell for less than $250. AMD will ship a new high-end product later this year, but the bread-and-butter of the gaming market is in cheaper cards.
This is AMD's reference-design Radeon HD 6870 with 1GB of GDDR5 memory.
We expect there will be some initial confusion amongst consumers, since AMD’s branding makes the cards look like replacements for the Radeon HD 5850 and Radeon HD 5870. But with an estimated retail price of $180, the Radeon HD 6850 is actually replacing the Radeon HD 5830, while the $240 Radeon HD 6870 will supplant the Radeon HD 5850. Nvidia has dominated the market at those price points to date, thanks to its 768MB and 1GB GeForce GTX 460 SKUs.
AMD is busy working on a new high-end GPU, code-named Cayman, but the company hasn’t revealed any details on timing or pricing at this point.
AMD had several goals for Barts:
Improve performance relative to die size – squeeze out more frames per second from a smaller chip.
Build a second generation DirectX 11 GPU with improved tessellation and geometry performance.
Enhance image quality significantly
Add new multimedia (video) features for improved performance and new capabilities
Build on top of Eyefinity and take advantage of next generation display technology, including DisplayPort 1.2 and HDMI 1.4a
The 6800 series currently offers between 12 and 14 SIMD (single-instruction/multiple data) blocks, with 80 stream processors per block. The Radeon HD 6870 ships with 1120 stream processors (14 SIMD blocks), while the HD 6850 has 960 stream processors (12 SIMD blocks). Both GPUs use the same die; the 6850 simply has two blocks disabled.
The 6800 series now includes two dispatch processors, each with its own instruction and data caches (the 5800 had only one). In addition to the second dispatch unit, the dispatch processor has been updated. The net result is improved thread management and buffering, allowing the GPU to keep more threads in flight to minimize stalling.
According to AMD, the tessellation unit has been significantly reworked, offering higher throughput. The 6800-series is built on a 40nm manufacturing process, but the both the 6850 and the 6870 boast higher clock speeds than the 5850 and 5870. The 6800’s tessellation unit works best when the application delivers around 16 pixels per polygon. At the extreme end, with one-pixel polygons, performance tends to trail off, though the tessellation rate still remains higher than the 5870 even at these extremes. At the sweet spot, tessellation performance is double that of the 5870.
Reference-design Radeon HD 6850 cards are slightly shorter than their more powerful siblings.
While we can’t dive into many details here, AMD also added additional antialiasing features, particularly morphological AA. Morphological AA is actually a post-processing AA technique accelerated using Microsoft’s DirectCompute API. What’s cool about it is that it detects all edges, not just polygon edges, so it can apply antialiasing to texture edges as well. It’s also faster than super-sampling. Morphological AA won’t be enabled in AMD’s Catalyst drivers until later this year; but since it’s a post-processing feature, it will work with DirectX 9, 10 and 11 games.
AMD has also improved its Eyefinity multi-monitor technology. Reference-design cards have five display connectors: two mini-DisplayPort 1.2 connections, one HDMI 1.4a, one dual-link DVI, and one single-link DVI. Third-party manufacturers, however, are free to ship different configurations.
We didn’t have time to run in-depth CrossFire benchmarks, but the performance scaling we did see was impressive—we’re talking a very close to 2x performance boost running two cards in CrossFire mode. That’s considerably better than what we’ve seen running any two 5800-series cards. A pair of 6850’s running in CrossFire will be a potent gaming configuration for just $360.
The tech industry has a difficult time keeping secrets, and AMD has had particularly hard time of it this time around. Those leaks gave Nvidia the opportunity to launch a preemptive strike by lowering its prices: The GeForce GTX 460 with 1GB of memory have dropped to less than $200 (although some manufacturers are using mail-in rebates to get there), and the GTX 470 will sell for less than $260 (or even less, when you take mail-in rebates into account)—but both those prices are till higher than the average price of a Radeon HD 6870.
Overall, it’s looking like AMD has a pair of winners on their hands. By offering greater efficiency, interesting new display features, and improved performance at attractive price points, AMD is stepping up the pressure on its main rival. The net result is faster frame rates for less money, and that’s a win for PC gamers.
You’ll find our hands-on review of XFX’s Radeon HD 6850 here, and our review of XFX’s Radeon HD 6870 here.