Shader Model 4 supports a new pipeline stage-the geometry-shader stage-which can be used to create or modify existing geometry. Geometry shader registers (see Registers - gs_4_0 and Registers - gs_4_1).
Vertex shader registers (see Registers - vs_4_0 and Registers - vs_4_1).Pixel shader registers (see Registers - ps_4_0 and Registers - ps_4_1).The register set is accessible through members in constant and texture buffers using HLSL semantics for things like component packing.
It has been designed using a common-shader core that gives a common set of features to all programmable shaders, which are only programmable using HLSL. Shader Model 4 is a superset of the capabilities in Shader Model 3, except that Shader Model 4 doesn't support the features in Shader Model 1.
