Next-Gen ATI Cayman Chip to Feature Substantially Modified Architecture - Slides.

First Nearly Official Details About AMD Radeon HD 6900 "Cayman" Chip Emerge

by Ilya Gavrichenkov
11/22/2010 | 07:02 PM

A web-site has published slides from an alleged presentation by Advanced Micro Devices that describe capabilities of the next-generation code-named Cayman graphics processor. The new family of chips known as AMD Radeon HD 6900 will feature rather massively redesigned DirectX 11 architecture, which should ensure higher performance compared to currently available graphics cards as well as add some new features.

 


Image from alleged AMD Radeon HD 6900-series presentation published by NGOHQ web-site.

The most important modification of the Cayman compared to the predecessor is the change of the stream core (SC) to the so-called VLIW-4 (very long instruction word) architecture. Previous-generation graphics processors featured VLIW-5 architecture stream cores and each of the SCs featured four simple arithmetic logic units (ALUs, or processing elements as developers sometime call them) for simplistic operations and one so-called transcendental arithmetic logic unit capable of performing one complex instruction per clock. The new four ALUs are neither simplistic nor complex and can perform up to 4 FMA (or 4MAD or 4 MUL of 4 ADD, etc) operations per clock. According to developers, such architecture saves around 10% of die area while maintaining similar performance and simplifies scheduling and register management.


Image from alleged AMD Radeon HD 6900-series presentation published by NGOHQ web-site.

Another key improvement for the ATI Radeon HD 6900 "Cayman" is doubling of graphics engines within the chip. The graphics processing unit now has two rasterizers, two geometry assemblers, two vertex assemblers and two tessellators with off-chip buffer support. Even though the Radeon HD 5800 "Cypress" and the Radeon HD 6900 "Barts" chips also featured two rasterizers and other elements of the graphics engines, this time the engines seems to be more independent and higher performance, as a result, their performance should be significantly higher compared to predecessors.


Image from alleged AMD Radeon HD 6900-series presentation published by NGOHQ web-site.

Additional improvements include new render back end units, support of higher-quality antialiasing, improvements aimed at general purpose computing on GPUs as well as new power management engine.


Image from alleged AMD Radeon HD 6900-series presentation published by NGOHQ web-site.

One of the things that the presentation does not reveal are precise specifications of the Radeon HD 6950 and 6970 graphics cards. What we do know is that a fully-fledged Cayman features over 20 SIMD engines with 16 stream cores (that feature 4 processing elements) per each; one SIMD features 64 stream processors. We also do know that the chip has over 1600 processing elements, over 80 texture units 32 improved raster operating units as well as 256-bit memory bus. Some believe that the Cayman chip sports 30 SIMD engines and 1920 stream processors.


Image from alleged AMD Radeon HD 6900-series presentation published by NGOHQ web-site.

According to manufacturers of graphics cards, the Radeon HD 6970 should be 30% - 50% faster compared to the Radeon HD 6870. The novelty is projected to become available in December, 2010.