Also known as: Form factor
A motherboard form factor is a standardized specification for a motherboard’s physical size, shape, mounting-hole positions, and connector placement, so that boards, cases, and power supplies from different makers fit and work together.1
Overview
By fixing dimensions and the location of mounting holes, the rear I/O panel, expansion slots, and the power connector, a form factor turns PC parts into interchangeable building blocks. The common desktop standards descend from Intel’s ATX: full-size ATX (~305 × 244 mm) with the most slots and ports, smaller Micro-ATX for compact builds, and tiny Mini-ITX (170 × 170 mm) for small-form-factor machines. Larger E-ATX boards serve high-end workstations. A given computer case lists which form factors it accepts, and a power supply unit follows matching standards.
Where it fits
The form factor is the first decision in a desktop build because it caps everything downstream: how many PCI Express and RAM slots you get, how much room there is for cooling, and how small the case can be. Bigger boards mean more expansion and easier airflow; smaller ones save space at the cost of slots. Pre-built all-in-one computers and mini PCs often use proprietary boards, trading this standardization for compactness.
Sources
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Computer form factor — Wikipedia, on motherboard form-factor standards. ↩