How do you find form factor?

ATX board dimensions are 9.6" wide by 12" long.
µATX board dimensions are 9.6" wide by 9.6" long.

Biggest difference ATX boards usually have five or six PCI slots. Where as µATX boards usually have three or four PCI slots.

<font color=red><i>Happy Canuck</i>!</font color=red> ' '

An AT board has one row of pins for the powercable, and an ATX board has a double row of pins.

My case has so many fans that it hovers above the ground .

Just fyi: I know they aren't that popular, and I'm probably the only goofball here that's really interested in building a system based on them, but there is also the FLEX-ATX specification. I believe that the flex ATX form factor was introduced by Intel back in 1999 (help me out, experts?). The dimensions typically run 9.0"x7.5", I think. They are primarily used in industrial computers, rack systems and some small desktop pc's. Most only have one PCI slot (some two), and even fewer have AGP slots, as they typically have on board GPUs (though not stellar ones). They also tend to have onboard ethernet adapters and modems. The ones Ive run across are usually Socket 370, so they are limited in the type of processor you can use. A few new flex ATX boards use Socket 478 now. Problem is most of the cases for them only have 150watt Power Supplies! Hampers your expansion options a bit.

quick plug---> My interest in them is trying to build a powerful platform, which is lightweight, has a small desktop footprint, runs COOL, and is relatively attractive compared to the typical grey boxes littering desktops everywhere. I feel like if the Appleheadz can do it, PC's can probably do it better (with a little thought).