DirectX 9 was released on December 24, 2002.
WIndows 98SE introduced DirectX 8 which introduced a new high level shader language. The goal with the shader was to allow various new algorithms to be used as research into computer graphics was still expanding.
Now DX9 has a new shader model which is a refinement of the original model. Now much longer shaders are possible as it was realized that the original implementation was too restrictive.