Computer-on-module

COMs are complete embedded computers built on a single circuit board.[1] The design is centered on a 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 usually lacks the standard connectors for any input/output peripherals to be attached directly to the board.

The module usually needs to be mounted on a carrier board (or "baseboard") which breaks the bus out to standard peripheral connectors. Some COMs also include peripheral connectors. Some can be used without a carrier.

A COM 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. As a COM is very compact and highly integrated, even complex CPUs, including multi-core technology, can be realized on a COM.

Some devices also incorporate field-programmable gate array (FPGA) components. FPGA-based functions can be added as IP cores to the COM itself or to the carrier card. Using FPGA IP cores adds to the modularity of a COM concept, because I/O functions can be adapted to special needs without extensive rewiring on the printed circuit board.[2]

The terms "Computer-on-Module" and "COM" were coined by market researcher Venture Development Corp (VDC) and first appeared in VDC's report on the Global Market for Merchant Computer Boards in Real-time and Embedded Applications[3], published in November 2001. The terms became more prominent upon industry standardization of the COM Express format in 2005.

There is no clear "first Computer-on-Module" product, since numerous small component-like single board computers were already on the market[4][5] when VDC initially introduced the term.

COM Express is just one of many standardized Computer-on-module formats. Other open-spec COM standards include SMARC, Qseven, ESM, XTX, and eTX. Additionally, many manufacturers offer COMs with proprietary formats.

Some proprietary COM formats have modified SODIMM and MXM edge-connector style designs, while others have arbitrary rectangular dimensions along with various types of high density board-to-board connectors [6][7]. Notably, the Raspberry Pi Compute Module is designed in a 200-pin SODIMM format.

Using a carrier board is a benefit in many cases, as it can implement special I/O interfaces, memory devices, connectors or form factors. Separating the design of the carrier board and COM makes design concepts more modular, if needed. A carrier tailored to a special application may involve high design overhead by itself. If the actual processor and main I/O controllers are located on a COM, it is much easier, for example, to upgrade a CPU component to the next generation, without having to redesign a very specialized carrier as well. This can save costs and shorten development times. However, this only works if the board-to-board connection between the COM and its carrier remains compatible between upgrades.

Other benefits of using COM products instead of ground-up development include reducing time to market (TTM), risk reduction, cost savings, choice of a variety of CPUs, reduced requirements and time for customer design, and the ability to conduct both hardware and software development simultaneously [8].

• COM Express
• CoreExpress
• Embedded System Module
• ESMexpress
• ETX (form factor)
• Qseven
• SMARC
• XTX