Although distributed ray tracers produce better photorealistic images than traditional ones, they are considerably slower due to extra oversampling rays they shoot.
Common techniques resort to both software and hardware to accelerate the computations.
However, there are other approximation algorithms that could achieve even better performance gain without special software or hardware. It is based on the classification of shadows. In cases where a point is either in light or umbra, there is no need to shoot oversampling rays for the intersection point. Only when the point is found to be under penumbra it's necessary to invoke the expensive soft shadow oversampling to determine the percentage of light seen by the point. And, to determine whether a point is under penumbra, only a constant two extra rays are needed.