[sipherhex]

Disclaimer: I work in the GPU industry.

If you're interested in the architecture of a GPU this Berkeley ParLab presentation by Andy Glew from 2009 covers the basics of how the compute cores in modern GPUs handle threading. It's a subtle, but powerful, difference from SIMD or vector machines.

http://parlab.eecs.berkeley.edu/sites/all/parlab/files/20090...

If you want to get into the details of how a GPU interfaces with the system and OS software, which is almost an entirely other animal, you may want to look at the Nouveau project to get oriented.

http://nouveau.freedesktop.org/wiki/