COM Express is a family of modular, small form factor computer-on-module (COM) specifications for mid-range edge processing and networking that has become one of the most popular embedded hardware standards in the world.
Since its initial ratification in 2005, COM Express has spawned eight different Types, four different sizes, and three major revisions while retaining a modular architecture that promotes vendor interoperability and technology reuse.
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Key Features and Benefits
The primary feature that sets COM Express apart from traditional single-board computers (SBCs) is the ability to plug off-the-shelf COM Express modules into custom carrier boards that provide application-specific I/O. In other words, the architecture consists of:
A standardized compute module that contains processor(s), memory, and other core logic
A customizable carrier board that can be configured to meet a variety of application-specific requirements
A module connector that physically attaches the module to the board and provides high-speed, high-pin count signaling between the two
This dual-board architecture eliminates the high-speed interfacing and signal integrity expertise otherwise required to design their own processor modules. This reduces time to market, and provides a scalable roadmap where performance upgrades can be as simple as plugging a new COM Express module into an existing carrier board.
This same concept has been carried over to COM-HPC, which complements COM Express by extending the by extending performance and feature sets for more demanding applications.
Module Sizes
COM Express defines four module sizes (mini, Compact, Basic, and Extended) to accommodate a wide range of performance and space requirements across applications like industrial automation, robotics, medical, retail, digital signage, and gaming. Ruggedized and high-temperature products are also available for demanding applications including mil/aero, transportation, and remote data acquisition.
COM Express modules come in four sizes
The Mini Module (84mm x 55mm) is tailored for mobile applications that demand high integration, superior graphics capabilities, and extended battery life. It is equipped with a single 220-pin connector and supports a wide-range power supply input of 4.75-20V. Mini Modules often feature memory and SSD storage soldered directly onto the module, enhancing durability for rugged systems.
The Compact Module (95mm x 95mm) is designed for mobile and stationary systems that require a compact form factor without sacrificing performance. It features dual 220-pin connectors, for up to 440 pins of connectivity. The module can accommodate a horizontally-mounted SO-DIMM for memory expansion and offers options for 5mm and 8mm stack heights.
The Basic Module (125mm x 95mm) providing space for applications that need more memory or integrated features. Like the Compact Module, it utilizes dual 220-pin connectors and accommodates a single horizontal mount SO-DIMM.
The Extended Module (155mm x 110mm) is aimed at high-performance, feature-rich applications. It supports two full-size DIMM or mini DIMM memories, or two horizontal or vertical mount SO-DIMMs, providing flexibility in memory configuration. It also features dual 220-pin connectors and is capable of accommodating higher performance CPUs that are not supported by the smaller module sizes.
COM Express Types
COM Express modules connect to carriers and other hardware via standardized pinouts. Various pinout Types are defined that balance cost, features, and performance while maintaining common connectors and mounting holes and common signaling where appropriate.
The PICMG COM Express subcommittee maintains active working groups that focus on evolving the technology to meet the latest application requirements. The COM Express Module Base Specification has already undergone three major revisions, and the subcommittee is currently working on Rev 3.2.
Rev 3.1, the current version of the COM Express Base Specification, was released in summer 2022, updating the standard to support changes in peripheral interfaces such as USB4 with alternate mode for DisplayPort. Rev 3.1 modified Rev 3.0 in a few ways, most notably introducing new functionality and support to COM Express Type 6, 10, and 7:
Support for PCIe Gen 4, SATA Gen 3, and USB 4.0
Option for MIPI-CSI camera interfaces, separate from the COM Express connectors
Option for SoundWire instead of High Definition Audio (HAD)
Updated COM Express connector list to include 16 Gbps versions
Although Rev 3.2 of the COM Express Base Specification is not yet ratified, it will likely introduce similar changes to those that debuted in Rev 3.1, updating the three core module Types with support for new peripheral interfaces.
The following tables summarize notable features of Rev 3.1. Note that all Types offer 8 GPIO, SPI ports, and support IEEE 1588
The COM Express Module Base Specification Rev 3.1 defines three main Types.
