Many space-limited embedded applications require significant processing performance and substantial I/O capabilities in a compact form factor. Enter COM Express. (COM is an abbreviation for “Computer on Module”.) COM Express modules can serve as standalone boards by themselves or can be used as a processor mezzanine card. One very helpful feature of a COM form factor like COM Express is that your embedded designs can take advantage of several microprocessors operating at varying performance and power-consumption levels without making major board-level hardware changes to accommodate these different processors. The COM Express board design allows you to swap one COM Express module for another whenever your design needs a performance upgrade.

COM Express board-to-board connectors are arranged in two rows. One row provides I/O pins for PCI Express, LPC (Low Pin Count) Bus, SATA, LVDS LCD Channel, VGA and TV-out video, LAN, and system and power-management interfaces plus power and ground pins. The second row of pins provides SDVO (serial digital video out) and legacy IDE and PCI interface signals, additional PCI Express, and LAN interface pins, and additional power and ground pins. The maximum I/O support for a COM Express module is:


  • 32 PCI Express lanes (80Gbps aggregate)
  • x16 PCI Express graphics
  • 2 LVDS Channels
  • 2 SDVO Channels
  • 4 SATA-150 links (600MBps aggregate)
  • 3 10/100/1000 Ethernet ports (10G provisions in the future)
  • 8 USB 2.0 ports


Figure 1: This mechanical diagram from the PICMG COM Express Carrier Design Guide illustrates the pin usage on a COM Express module’s double row of board-to-board connectors

COM Express CPU modules come in two sizes - Basic and Extended - measuring 125x95mm and 155x110mm, respectively. The Extended Form Factor has a larger power budget, doubles the memory capacity, and allows the use of physically larger processors and chipsets. Both Basic and Extended COM Express form factors share the same board-to-board connections, signaling definitions, and mechanical assemblies so that a properly designed carrier board can accept both Basic and Extended COM Express modules.


Figure 2: This mechanical diagram from the PICMG COM Express Carrier Design Guide juxtaposes the Basic and Extended COM Express module formats and shows the double row of board-to-board connectors

A design approach based on the COM Express form factor creates an embedded-computing solution that provides significant processing and I/O bandwidth in a relatively small physical footprint. Many embedded applications in a wide range of diverse markets including interactive kiosks, gaming units, industrial automation and controls, security and surveillance systems, retail self-serve checkout terminals, training simulators, digital signage, and medical devices (just to name a few of the many possible embedded applications) can take advantage of the COM Express architectural features by simply providing a double row of pins for the board-to-board interface. The system designer need only select a COM Express module with appropriate performance and I/O capabilities and plug it in. Upgrading the computing hardware at a later time becomes a simple matter of plugging in a new COM Express module.

There is a direct relationship between an organization’s ability to quickly implement and deploy hardware upgrades and how quickly that organization will see an ROI based on the improved end product. The plug-and play nature of COM Express can help to quickly generate new revenue streams through rapid end-product development and deployment. Simply stated, the COM methodology allows an organization to rapidly respond to demand fluctuations, competitive forces, and the latest semiconductor advances by quickly and efficiently modifying existing designs with plug-in COM Express hardware.

There are many commercial off-the-shelf COM Express modules available based on a wide range of Intel® processors. The table below shows some of the available COM Express modules from a product list at the PICMG web site (see reference below) and you can search for COM Express modules at the Intel® Embedded Alliance Solutions Directory at


Kontron and RadiSys are Premier members of Intel® Embedded Alliance; Adlink is an Associate member of the Alliance; and Arbor Technology Corp, Diversified Technology, Inc., and MSC Vertriebs GmbH are Affiliate members of the Alliance.

Have you implemented an embedded design with a COM Express board? What was your experience? How have you used the module interchange capability of this form factor to good effect?

Note: This blog entry is based on the article “The Economics and Use of COM Express in Embedded Applications” by Doug Mays, Technical Marketing Specialist, Diversified Technology, Inc. ( and the COM Express product listing at the PICMG web site.

Steve Leibson
Roving Reporter (Intel Contractor)
Intel® Embedded Alliance