PC Perspective gaves you an update on ray tracing and gaming to give you a perspective on what changed since early 2007:
If you are new to the topic of ray tracing you might want to read through this section. Ray tracing is a rendering technique that generates a 2D image out of a given 3D scene. This is done by simulating the physics of light propagation using rays. The algorithm shoots, for every pixel on the screen, a so-called "primary ray" from the perspective of the eye of the viewer. The ray tracing algorithm then determines which object is hit first on the path of the ray.