In Mark's famous folding farm thread he was using bare motherboards sitting on a rack in the computer room at his work place. They were basically a mother board, CPU/Fan, RAM, and a power supply. In fact, he was splicing in an extra power harness and running two mother boards off of one power supply. Nothing else, not even a case. He was running them on Linux, diskless, headless, etc and booting them over the network. Towards the end, his avatar was a pic of the computer rack.
Pudge
EDIT: I can't believe it, I actually found a thread with pictures of
Mark's Mega Monster folding farm, as he called it. In the last post of the thread, Mark said he was using ECS K7S5A mother boards with AMD Athlon XP 2100+ CPUs. I was wrong about Mark using one power supply for two mother boards. While researching this, I found out it was dwjj who used to do this.
Here is the SS51G cluster referred to in the second post of Mark's Mega Monster folding farm thread. I wonder how many points a day that cluster could crank out.
