Yeah, I keep seeing that.....Okay, So 5 rigs with 4 5850s each. I think that is the past I'll take.
After choosing your graphics cards, its important to now consider the number of rigs. As with GPUs, there are several independent features to optimize ...
1. Fewer motherboards, i.e. five rigs, mean fewer disk drives or USB sticks to contain the operating system, fewer CPUs, fewer network cables, less shelf space, and easier hardware monitoring - in that you either have to hook up a monitor, mouse and keyboard to a motherboard in order to work on it, or using Linux, e.g. linuxcoin, one can ssh into the rig to see all the attached graphics cards. Fewer motherboards may mean fewer power supplies, but gaming-style power supplies can be more expensive when capable of powering say four overclocked 5850s - maybe 1200 watts per single power supply or simply two less expensive power supplies per motherboard. Motherboards having four PCIe slots are more expensive than those having say two PCIe slots. See the forum thread for mining rig photographs for ideas on how to cool packed GPU cards, or to move them away from the motherboard using PCIe extension cables.
2. More motherboards, i.e, ten rigs with two 5850s each, on the other hand may be more expensive in total than the alternative (1) above, but they are far easier to cool - as the cards are twice as far apart and the GPU fans have a much better inflow. Commodity motherboards permit the use of much less expensive power supplies - say 600 - 850 watts apiece.
3. Consider whether to enclose the rigs in cases. Operating without a case may violate certain consumer protection laws against electronic emissions but the practical reality is that many miners, and myself do so. Cases very much restrict airflow, but compensate somewhat by adding fans. If noise and component clutter are not an issues, consider operating without cases. Again, one can get many ideas from the mining rig photos posted in the hardware forum.
