How it works
A form factor describes physical dimensions and mounting arrangements. It helps determine whether a motherboard fits a case or a drive fits its housing. It does not establish every electrical or functional compatibility rule. For example, a component may fit into the available space but use an unsupported interface, exceed cooling clearance or require a power connection the system lacks. Size labels must therefore be read alongside the detailed specification.
Desktop assembly involves several interacting dimensions: motherboard mounting points, power-supply format, graphics-card length and thickness, cooler height and available cable space. A smaller case can impose different limits on each. Laptop parts are often even more model-specific. A memory module's physical format is separate from its memory generation, just as an M.2 drive's length does not establish whether it uses SATA or NVMe.
Practical checks
Before ordering, record the exact case or device model and compare every relevant clearance with the component documentation. Allow room for connectors and airflow rather than measuring only the main body. Confirm electrical interface, firmware support and power requirements independently. If a part does not seat normally, stop instead of forcing it. A compatibility check should explain both why the component fits and why the system can actually use it.