|This article does not cite any references or sources. (October 2011)|
COM Express, a computer-on-module (COM) form factor, is a highly integrated and compact PC that can be used in a design application much like an integrated circuit component. Each COM Express Module COM integrates core CPU and memory functionality, the common I/O of a PC/AT, USB, audio, graphics (PEG), and Ethernet. All I/O signals are mapped to two high density, low profile connectors on the bottom side of the module.
The COM Express standard was first released in 2005 by the PCI Industrial Computer Manufacturers Group (PICMG) and it sought to provide standardized module interfaces for several different target applications. It did so by defining five different module "Types" each implementing different pinout configurations and feature sets on one or two 220-pin connectors. In that way, COM Express is a standard of multiple standards. It also defined 2 module sizes (later expanded to 4) to allow additional flexibility to better serve the end application while maintaining compatibility within each module "Type." 
There are 7 different pin outs defined in the specification. The most common used pin out is type 2. The latest pin-outs added in the revision 2.0 of the COM Express specification (available from www.picmg.org) are Type 6 and Type 10.
Maximum available interfaces for the defined types:
- Type 1: Single connector (220 pin), 6 PCI Express lanes, no PEG, no PCI, no IDE, 4 SATA, 1 LAN
- Type 10: Single connector (220 pin), 4 PCI Express lanes, no PEG, no PCI, no IDE, 2 SATA, 1 LAN, single channel LVDS only, DDI, no VGA, 2 Serial COM
- Type 2: Double connector (440 pin), 22 PCI Express lanes, PEG, PCI, 1 IDE, 4 SATA, 1 LAN
- Type 3: Double connector (440 pin), 22 PCI Express lanes, PEG, PCI, no IDE, 4 SATA, 3 LAN
- Type 4: Double connector (440 pin), 32 PCI Express lanes, PEG, no PCI, 1 IDE, 4 SATA, 1 LAN
- Type 5: Double connector (440 pin), 32 PCI Express lanes, PEG, no PCI, no IDE, 4 SATA, 3 LAN
- Type 6: Double connector (440 pin), 24 PCI Express lanes, PEG, no PCI, no IDE, DDI (for DisplayPort, HDMI, DVI or SDVO), 4 SATA, 1 LAN, 2 Serial COM, USB 3.0
The specification defines 4 module sizes:
- Mini: 55 × 84 mm (2.2 × 3.3 in); formerly known as nanoETXexpress
- Compact: 95 × 95 mm (3.7 × 3.7 in); formerly known as microETXexpress
- Basic: 95 × 125 mm (3.7 × 4.9 in); formerly known as ETXexpress
- Extended: 110 × 155 mm (4.3 × 6.1 in)
The COM Express specification is hosted by PICMG. It is not freely available but may be purchased from the PICMG website.
The current revision 2.1 (PICMG COM.0 R2.1) was released in May 2012. The original revision 1.0 was released July 10, 2005.
|Dimensions||95 × 114 mm (3.7 × 4.5 in)||95 × 114 mm (3.7 × 4.5 in) (ETX footprint)||
|Legacy1 support||Full legacy||Legacy except ISA||Legacy except ISA|
|PCI Express support||-||4 Lanes||up to 6 Lanes (basic)|
|PCI Express Graphic support||-||-||up to 16 Lanes|
|IDE support||2 IDE, 2 SATA2||2 IDE, 4 SATA||IDE, 4 SATA|
|USB support||4 USB||6 USB||8 USB|
|Audio support||Line In/Out, Mic||AC'97, Line In/Out, Mic||AC'97, Line In/Out, Mic, AC'97 digital, HDA|
|Power||5V, 5VSB||5V, 5VSB||12V, 5VSB|
- PICMG website
- The Economics and use of COM Express in Embedded Applications
- COM Express Carrier Design Guide - Guidelines for designing COM Express Carrier Boards
- Purchase specification (scroll down to "PICMG COM.0 R2.1")
- COM Express Plug-and-Play Initiative
- COM Express: Scalability and flexibility for UAS sensor processing