I've added a new page, Real-Time Ray Tracing with NVIDIA CUDA GPGPU and Intel Quad-Core. I've created two new versions of the ray-tracer code, one utilizing NVIDIA CUDA, and another using pthreads to exercise multi-core CPUs. The CUDA code is fastest, but least realistic as a practical ray-tracer. Pthreads was certainly easiest -- a half hour change to pre-existing generic code. I think CUDA will perform much better on more constrained (in terms of control flow and random memory access) algorithms.