A computer-on-module (COM) is a type of single-board computer(SBC), a subtype of an embedded computer system. It is also called System on Module(SOM) as an extension of the concept of System on Chip (SoC) and lying between a full-up computer and a microcontroller in nature.
Today's COM/SOM modules are complete computers built on a single circuit board. The design is centered on a single microprocessor with RAM, input/output controllers and all other features needed to be a functional computer on the one board. However, unlike a single-board computer, the COM module will usually lack the standard connectors for any input/output peripherals to be attached directly to the board. Instead, the wiring for these peripherals are bussed out to connectors on the board.
The module will usually need to be mounted on a carrier board (or "baseboard") which breaks the bus out to standard peripheral connectors. Some COMs also include peripheral connectors and/or can be used without a carrier.
A COM/SOM solution offers a dense package computer system for use in small or specialized applications requiring low power consumption or small physical size as is needed in embedded systems.
Some devices also incorporate Field Programmable Gate Arrays.
The terms "Computer-on-Module" and "COM" were coined by Venture Development Corporation (Natick, MA, USA) to describe this class of embedded computer boards. The term became more notable upon industry standardization of the COM Express format.
A number of manufacturers offer products which are defined as system-on-module or computer-on-module. Among those are Advanced Knowledge Associates (www.a-k-a.net) in Santa Clara, CA; BCM Advanced Research (www.bcmcom.com) in Irvine, CA; Embedded Systems (www.embedded-systems.net); MEN Micro (www.menmicro.com) in Ambler, PA; DAVE Embedded Systems (www.dave.eu) in Italy.