Form factors

For computing hardware, a form factor designates the dimensions, shape, and other physical characteristics of a computer case and its contents, including the power supply, mountings for internal storage devices, the motherboard and its mountings, RAM, expansion cards, the socket for the microprocessor, and other slots and mountings. The image that follows shows a variety of motherboard form factors, each of which have been made to fit inside a computer case of the same form factor. An ATX motherboard mounts in an ATX computer case, for example:

Motherboards in five different form factors
Image courtesy: VIA Technologies, Inc

Tower servers

It's common, especially in smaller networks and some home networks...