[compsciphd]

one can start a fire before the sabbath and benefit from its heat. One can't stoke the fire (to make it hotter) or extinguish it. On the flips side (as an example only) if I was sitting around a camp fire that I lit before the sabbath with a non jew, and he wanted to extinguish it or stoke it for his own benefit (I might benefit as well, but he's supposed to be doing it for his own benefit) that would be permitted.

apply to a computer: one can let it keep on doing what it is doing, but he owner wouldn't manipulate it.