A chassis (pronounced TCHA-see or CHA-see ) is the physical frame or structure of an automobile, an airplane, a desktop computer, or other multi-component device. Case is very similar in meaning, but tends to connote the protective aspect of the frame rather than its structure. People tend to choose one term or the other. The rest of this definition uses chassis but applies as well to the term case . Both terms (and casing ) are derived from the Vulgate Latin for box . The plural form is also chassis .
In a computer, the chassis houses the main electronic components, including the motherboard (with places to insert or replace microchips for the main and possibly specialized processors and random access memory ( RAM ) and places for adding optional adapters (for example, for audio or video capabilities). Typically, room is provided for a hard disk drive and a CD-ROM drive.
The IBM PC chassis for its XT computers set an early de facto standard for a chassis configuration (sometimes referred to as the form factor ). The desktop computer has since evolved through the AT model, the mini-AT, and the small-footprint PC. A later development was the vertical or tower chassis configuration, designed to be placed under a desk. The outer dimensions of a chassis are said to form its footprint .
The term is not usually applied to mobile and notebook computers perhaps because the hardware components have to be more tightly integrated. Some communications devices such as terminal servers have a chassis especially designed to handle many combinations of hardware add-ons. Such a chassis is described as modular .