System on module

A system on a module (SOM) is a board-level circuit that integrates a system function in a single module. It may integrate digital and analog functions on a single board. A typical application is in the area of embedded systems. Unlike a single-board computer, a SOM serves a special function like a system on a chip (SoC). The device integrated in the SOM typically requires a high level of interconnection for reasons such as speed, timing, bus-width etc., in a highly integrated module. There are benefits in building a SOM, as for SoC; one notable result is to reduce the cost of the base board or the main PCB. Two other major advantages of SOMs are design-reuse and that they can be integrated into many embedded computer applications.
History.
The acronym "SOM" has its roots in the blade-based modules. In the mid 1980s, when VMEbus blades used mezzanine modules, these were commonly referred to as System On a Module (SOM). These SOMs performed specific functions such as compute functions and data acquisition functions. SOMs were and still are extensively used by Sun Microsystems, Motorola, Xerox, DEC, and IBM in their blade computers.
Design.
A typical SOM consists of: