Towers are available in a variety of form factors, or shapes and sizes. Although they can range in
height from 12 inches to 30 inches or more, the trend is toward smaller desktop tower form factors. Some desktops, called an all-in-one desktop, do not have a tower and instead house the screen
and system unit in the same case. Many peripheral devices, such as keyboard, mouse, printer,
speakers, and external hard disk, often occupy space outside a system unit.