PC/104

PC/104 (or PC104) is an embedded computer standard controlled by the PC/104 Consortium which defines both a form factor and computer bus. PC/104 is intended for specialized embedded computing environments where applications depend on reliable data acquisition despite an often extreme environment. The form factor is often sold by COTS vendors, which benefits many consumers who want a customized rugged system without committing months of design and paperwork.

The PC/104 form factor was originally devised by Ampro in 1987 (led by CTO Rick Lehrbaum), and later standardized by the PC/104 Consortium in 1992. An IEEE standard corresponding to PC/104 was drafted as IEEE P996.1, but never ratified.

Unlike the popular ATX form factor which utilizes the PCI bus and is currently used for most PCs, the PC/104 form factor has no backplane, and instead allows modules to stack together like building blocks. The stacking of buses is more rugged than typical bus connections in PCs. This is a result of mounting-holes in the corner of each module, which allow the boards to be fastened to each other with standoffs.

The standard size of boards complying to the form factor is 3.55 × 3.775 inches (90.17 × 95.89 mm), while the height is typically constrained to the boundaries of the connectors. A constrained height region is intended to guarantee that modules will not interfere with their neighbors. Vendors often follow these design restrictions to ensure proper stacking of modules, although it is not uncommon to find boards which ignore the form factor requirements.

While a typical system (also referred to as a stack) includes a motherboard, analog-to-digital converter, and digital I/O (data acquisition) module, other peripherals are finding their way into the market including GPS receivers, IEEE 802.11 controllers, and USB controllers.