The form factor determines the specifications on how a motherboard is built, from the size, shape, casing, power supply, mounting holes, and the overall layout. The most common form factor is ATX, which evolved to mini-ATX, nano-ATX, pico-ATX, and further
Form factor for computers refers to the size, shape, and physical specifications of hardware or hardware components. Computer form factor is used to describe any physical aspect of a computer system. Form factor is very important for connection compatibility.