Motherboard Form Factors

The most important component in a PC system is the main board or motherboard. The various types of motherboards available and those components typically contained on the motherboard interface connectors. Several common form factors are used for PC motherboards. The form factor refers to the physical dimensions (size and shape) as well as certain connector, screw hole, and other positions, type of case the board will fit.
motherboard form factors are:
Obsolete Form Factors
Baby-AT
Full-size AT
LPX (semiproprietary)
Modern Form Factors
ATX
Micro-ATX
Flex-ATX
NLX
WTX (no longer in production)
All Others
Proprietary designs
Industry-Standard Motherboard Form Factors
Form Factor Use
ATX Standard desktop, mini-tower, and full-tower systems; most common form factor today; most flexible design for power users, enthusiasts, low-end servers/ workstations, and higher-end home systems; ATX boards support up to seven expansion slots
Mini-ATX A slightly smaller version of ATX that fits into the same case as ATX. Many so called ATX motherboards are actually mini-ATX motherboards; mini-ATX boards support up to six expansion slots
Micro-ATX Mid-range desktop or mini-tower systems
Flex-ATX Least expensive or low-end small desktop or mini-tower systems; entertainment or appliance systems
NLX Corporate desktop or mini-tower systems; fast and easy serviceability
WTX Mid- to high-end workstations and servers (withdrawn)