Unified Shader Model - Unified Shading Architecture

Unified Shading Architecture

When graphics hardware supports Unified Shader Model, it can make sense to design its computational units so that any of them can run any type of shader. When computational units are "unified", that is called Unified Shading Architecture. Most often such hardware is composed of an array of computing units and a dynamic scheduling / load balancing unit that distributes shader work to the computing units.

Hardware is not required to have Unified Shading Architecture to support Unified Shader Model, and vice versa. OpenGL 3.3 level hardware can still have dedicated vertex, geometry and pixel processors (although because of very similar ISA, they would be quite similar on hardware level). A technologically earlier (e.g. Shader Model 3.0) hardware can also have unified architecture, as is the case with Xenos graphics chip in Xbox 360, for example.

Unified Shader Architecture allows more flexible use of the graphics rendering hardware. For example, in a situation with a heavy geometry workload the system could allocate most computing units to run vertex and geometry shaders. In cases with less vertex workload and heavy pixel load, more computing units could be allocated to run pixel shaders.

Graphics processors that have unified shading architecture include the Nvidia GeForce 8 series, Geforce 9 series, GeForce 200 Series, GeForce 400 Series, GeForce 500 Series, GeForce 600 Series, ATI Radeon HD 2000, Radeon HD 3000, Radeon HD 4000, Radeon HD 5000 series, Radeon HD 6000 series and Radeon HD7000 series S3 Chrome 400, Chrome 500, Intel GMA X3000 series, Xbox 360's GPU and others like the Qualcomm Adreno series.