The GPU, New Image Quality Features
Those of you that are familiar with AMD’s previous DX11-class GPUs should find the block diagram below very familiar. The new GPU—codenamed ‘Barts’—at the heart of the Radeon HD 6800 series borrows heavily of the previous generation, but it is refined in a number of ways. AMD states the new architecture offers up to 35% better performance per square mm, within a similar power envelope and that tessellation and geometry throughput has been increased. In addition, Barts offers new anti-aliasing modes, enhanced anisotropic filtering, and a host of display output and media acceleration updates.
The new Radeon HD 6800 series GPU, in its full configuration offers up to 2 TeraFLOPS of compute performance with a peak fillrate of over 24Gigapixles/sec. The tessellation unit has been upgraded over the previous generation to offer approximately double the performance in real-world gaming scenarios and it now has dual rasterizers to keep the chip fed and running more efficiently. In its full configuration, which is employed in the Radeon HD 6870, Barts has 14 SIMD engines with 1120 steam processor cores, 56 texture units, 128 Z/Stencil ROPs, and 32 Color ROPs. In the 6850, two SIMD engines have been disabled, bringing the total number of stream processors enabled down to 960, but all 32 Color ROPs remain enabled. If you’re keeping track, the Radeon HD 5850 had 1440 total stream processors enabled, with 72 texture units, and the same number of ROPs.
Like the previous generation, the Barts GPU powering the Radeon HD 6800 series is manufactured using TSMC’s 40nm process node. The chip is comprised of “only” 1.7 billion transistors, whereas the previous-gen Cypress GPU had 2.15B, and has a die size of 255mm2. Cypress is 334mm2. That’s quite a sizable reduction is die size, for a GPU that should offer similar or better performance, thanks to refinements to the architecture and increased clock speeds.
As we’ve mentioned, the Barts GPU offers approximately double the tessellation performance of the previous generation. But it also offers enhancements designed to improve image quality as well. The improved anisotropic filtering algorithm of the Radeon HD 6800 series addresses some issues which caused some visual anomalies in the previous generation. The new algo now offers smoother transitions between filtering levels and maintains full performance, regardless of angle.
A new anti-aliasing mode is set to debut with the Radeon HD 6800 series as well, but since it’s a post-processing filtering technique, this new "Morphological" Anti-Aliasing mode may be available to Radeon HD 5800 series owners as well at some point. The Morphological AA feature is accelerated using DirectCompute and delivers full-scene antialiasing, but at speeds much faster than super-sampling. It is compatible with any DX9, 10, or 11 applications and is switchable via the Catalyst Control Center.
Other enhancements to the Barts GPU included a new Unified Video Decoder engine, bringing it up to UVD 3. The only major change here is that the new architecture can now accelerate DivX and xVid files as well. The Radeon HD 6800 series also features HDMI 1.4 and DisplayPort 1.2 support.