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. Because the standards share conventions, a case advertised for ATX also accepts the smaller Micro-ATX and Mini-ITX boards that mount on the same holes.
The common desktop standards descend from Intel’s ATX. A given computer case lists which form factors it accepts, and a power supply unit follows matching standards so the connectors line up regardless of who made each part.
Common sizes
The size you pick caps how much you can add later:
| Form factor | Size (mm) | PCIe slots (typ.) | RAM slots | Best for |
|---|---|---|---|---|
| E-ATX | 305 × 330 | 4–7 | 8 | High-end workstations |
| ATX | 305 × 244 | 4–7 | 4 | Standard desktop |
| Micro-ATX | 244 × 244 | 1–4 | 2–4 | Compact builds |
| Mini-ITX | 170 × 170 | 1 | 2 | Small-form-factor |
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. ↩