Once upon a time there was a pixel
Tiles and sprites for everyone (as long as they are only a few on each scanline).
Texture Mappers: 1995-1999
Polygon renderer that simply draws thing. You needed to transform, clip, light and everything on the CPU then you could give the final surface to the GPU for it to draw. The card did the texture mapping, z-buffering and rasterization.
- Voodoo Graphics - 1996
- Voodoo2 -1998
Fixed T&L: 2000-2002
Transform and lighting, added the ability for the GPU card to transform the vertices's and calculate the lighting for each one.
Shaders that made it possible to run a small custom program for each vertex and pixel. Separate hardware where allocated for pixel shader processing, vertex shader processing and texture mapping units.
Unified Shaders : 2008+
Instead of custom parts to handle vertex shaders or pixel shader unified shader computing units are used. Depending on the work that it needs to perform the GPU can select how many computing units will do each task.