About Computer System Cases and Form Factors

A computer case, also known as a computer chassis, cabinet, tower, box, enclosure, housing or simply case, is the enclosure that contains the main components of a computer. A computer case is sometimes referred to metonymously as a CPU, referring to the primary component housed within the case; this was a more common term in the earlier days of home computers, when peripherals other than the motherboard were usually housed in their own separate cases.

PC cases computer chassis are usually constructed from steel, aluminum, or plastic, although other materials such as wood, plexiglas, and Lego have also been used in case designs.

Computer cases can come in many different sizes, known as form factors. The size and shape of a computer case is usually determined by the form factor of the motherboard, since it is the largest component of most computers. Consequently, personal computer form factors typically specify only the internal dimensions and layout of the case. Form factors for rack-mounted and blade servers may include precise external dimensions as well, since these cases must themselves fit in specific enclosures.

For example, a case designed for an ATX motherboard and power supply may take on several external forms, such as a vertical tower or a flat desktop or pizza box. Full-size computer tower cases are typically larger in volume than desktop cases, with more room for drive bays and expansion slots. Desktop cases and mini-tower cases, designed for the reduced microATX form factor, are popular in business environments where space is at a premium.

Currently, the most popular form factor for desktop computers is ATX, although microATX and small form factors have also become very popular for a variety of uses. Companies like Shuttle Inc. and AOpen have popularized small cases, for which FlexATX is the most common motherboard size. Apple Inc. has also produced the Mac Mini computer, which is similar in size to a standard CD-ROM drive.

Computer tower cases come in mini-tower, mid-tower, and big-tower or full-tower sizes. Full tower cases are typically 30 inches or more in height and intended to stand on the floor. They have anywhere from six to ten externally accessible drive bays, with more bays only internally accessible. The ratio of external to internal bays is shifting, however, as computing technology moves from floppy disks and CD-ROMs to large capacity hard drives, USB flash drives, and network-based solutions. Midtower PC cases are smaller, about 24" high with two to four external bays. A minitower case will typically have only one or two external bays and stand from 12" to 18" tall.