Ray tracing has been around a surprisingly long time in computer graphics. It was used to generate images in the 1960s, and by the '80s new algorithms had been created including path tracing. Yet the "holy grail of rendering" remained a distant dream for early home machines like the ZX Spectrum. You need only look how long this machine takes to render a single ray-traced frame in order to get an idea of how far ray tracing acceleration has come in the past half-century.
It takes around 17 hours for the ZX Spectrum to render a single ray-traced frame. That's one frame every 61,200 seconds, or 0.000016 fps.
