What exactly is the size difference between the ATX and Micro ATX motherboard? My friend is getting a new MB and I'm trying to figure out which one he NEEDS. Mine is an ATX but I can't really tell that much of a difference. Thanks for any help guys!A Micro ATX motherboard is SMALLER in dimensions than an ATX motherboard and, therefore, will have fewer expansion slots. At most, you could have 3 PCI slots on a microATX board and many will only have 2 PCI slots, while a many full ATX boards will have 5 PCI slots.

The critical issue in deciding which motherboard to get is your computer case. "Full tower" ATX cases will always accommodate ATX motherboards. Most, but not all, Mid-tower cases will ALSO accommodate ATX motherboards. However, mini-tower cases will most likely only accommodate microATX boards, although some will accommodate ATX boards.

A microATX board can be often be installed in a full or mid tower ATX case; however, I suggest you verify this before buying a microATX board to put in a full or mid tower ATX case. If you do this type of INSTALLATION, you'll just have some slot openings on the back of your case that will never be USED.