What is a COM express module?

In this article:

  1. What Is A COM Express Module ?
  2. The Development of the COM Express Standard
  3. COM Express Standardised Board Form Factors
  4. Extended COM Express Boards with Type 7 'Server-on-Modules'

What Is A COM Express Module ?

COM Express is an embedded computing specification, a sub-type of Small Form Factor (SFF) computers and Computer on Module (COM) devices.

COM devices are modular computers, printed on a single printed circuit board as a complete computer, including RAM and microprocessor. They are a type of System on a Chip (SOC) and are standalone devices.

COM Express entered the market in 2005 and have since been progressing to meet the expanding uses of COM Express technology.

COM Express specifications are determined and regulated by PICMG – formally known as the PCI Industrial Computer Manufacturers Group – a “non-profit consortium of companies and organizations that collaboratively develop open standards.”

The COM Express product is one of many developed by PICMG, whose goals have been to take desktop PCI standards to industrial applications, with their technology having been used, in packaging, mechanical design, thermal design, system management and military computing applications.

The Development of the COM Express Standard

The COM Express standard was first released in 2005, by the PCI Industrial Manufacturers Group (PICMG) which sought to provide standardised 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.

COM Express is a standard of multiple standards. The latest COM Express specification was released in 2017 and is known as Revision 3.0.

  1. 2005 – COM Express Rev. 1
  2. 2009 – Carrier Board Design Guide Rev.1-Embedded EEPROM Spec
  3. 2010 – COM Express Rev. 2 – Embedded API (eAPI)
  4. 2012 – COM Express Rev. 2.1
  5. 2013 – Carrier Board Design Guide Rev. 2
  6. 2017 – COM Express Rev. 3
  7. 2018 – Ruggedised COM Express Kick Off – Short Form Specs

There are 8 different pin-outs defined in the COM Express specification.

The latest pin-out added in Revision 3.0 of the COM Express specification is Type 7. The most commonly used pinouts are Type 6 and Type 10.

COM Express Revision 3.0 removed legacy Type 1, Type 2, Type 3, Type 4, and Type 5, recommending that new designs should use the newer Type 6, Type 7 and Type 10 COMs.

COM Express Standardised Board Form Factors

The COM Express standard defines form factors and pinouts for Computer-on-Modules. The standard includes the mini form factor (84 x 55mm), the compact form factor (95 x 95mm), the basic form factor (125 x 95mm) and the extended form factor (155 x 125mm).

Each board is available with the following COM pin-out types:

  1. COM Express Mini – 84 x 55mm – COM Type 10
  2. COM Express Compact – 95 x 95mm COM Type 6
  3. COM Express Basic – 125 x 95mm COM Type 6 and 7
  4. COM Express Extended – 155 x 125mm COM Type 7

Extended COM Express Boards with Type 7 'Server-on-Modules'

The extended COM Express did not reach market relevance in the past. With the new, server-oriented pin-out Type 7, defined in the COM Express specification Revision 3.0, this might come into play, as server-type applications require more DRAM capacity and also look for more extreme CPU performance levels.

COM Express supports a maximum of 137 Watt power consumption. The larger size provides the real estate necessary for more memory and allows for better heat transmission, often essential with higher power consumption.

When comparing the new Type 7 pin-out to the Type 6 pin-out, it becomes obvoius that this will not be a replacement but that it targets headless server applications with low power consumption, high computing density and high I/O throughput.

When compared to Type 6, the new Type 7 definition removes all audio and video interfaces, the upper 4 USB 2.0, ExpressCard and the upper 2 SATA ports, freeing up 60 pins on the AB connector and another 42 pins on the CD connector. These 102 newly freed pins, in combination with some previously reserved pins, have been used to add extra PCI Express lanes and four 10 GB Ethernet KR lanes with a complete set of NC-SI sideband signals.

Type 7 COM Express modules can provide a range of features:

  1. 4x 10GBaseKR Ethernet with NC-SI
  2. 1x 1GB Ethernet
  3. 32x PCI Express 3.0 Lanes
  4. 2x SATA
  5. 8x GPIO shared with SDIO
  6. 2x Serial shared with CAN
  7. LPC bus shared with eSPI
  8. SPI and I²C bus
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