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by jason mcdonald, senior editor | read other blog posts

would that which we call a "computer-on-module" by any other name be as exciting? in this blog post, i explore the 'concepts' of computer-on-module, system-on-module and other emerging standards around the concept of splitting your single board computer into two parts. a 'module' which you can change quickly and easily, and a 'carrier board' which does not change so frequently and which can benefit from economies of scale and production. unfortunately, there is a lot of concept confusion and standards at war, here. consequently, this blog post hopes to take a stab at cutting thru the confusion.

contents of this post:

1. computer-on-module: the concept
2. com express: the most successful computer-on-module concept
3. computers on module: other competing standards
4. feedback - read it
5. feedback - give it

computer-on-module: the concept

The market for single board computers and embedded board computing is huge and growing. Rather than doing the entire board design themselves, many companies opt to work with an established provider of small form factor single board computers (sbc's) like a VersaLogic or a MEN Micro.

Beyond board standards and the emerging standards for computer-on-module (or often called system-on-module), I advise you to think really long and hard about your "board partner." More than choosing a standard - you are choosing a business partner, and you should make sure that they are reliable and honest as well as technologically savvy. Check out our Insiders' Guide: Selecting an Embedded Board for more details.

That said, one of the problems in the sbc marketplace might be called the problem of "reinventing the wheel" over and over and over again. Rather than respinning board after board with just minor (or even major) modifications, the bright lights of our industry got together and realized that it would be better to split the board design into two parts:

1. a carrier board which typically has the standardized CPU functions and other functions that do not change much board to board; and
2. a module wherein the peripherals and I/O in particular are designed out.

Conceptually, the idea is to place what is transferrable from one design to the next generally on the 'carrier board' and to place what is the 'unique' about each design onto the module. That said, it behooves you to choose your board partner (as much as your computer-on-module standard) because generally, you will be setting up a multi-board supply chain and you want to have a long term relationship with a reputable board partner to easily facilitate each new 'module' as well as any new 'carrier boards.' You want to ensure interoperability between your boards and modules. And in some cases, you want to leverage the board vendors' experience in other modules and carrier boards; indeed, you might even be able to buy some modules 'off the shelf,' to thereby lessen your cost and/or hasten the time to market for your application.

The computer-on-module concept has been most successful in the small form factor arena, and a number of vendors have helped to proliferate a number of competing standards. Target applications include medical, military, industrial, railway, transportion - anywhere and everywhere that a small, reliable 'computer' can be useful.

com express: the most successful computer-on-module concept

With the backing of Intel and Kontron, the most prominent computer-on-module standard in recent times is the COM Express standard:

The COM Express specification defines two module sizes. The basic module is 95 mm x 125 mm, while the pin compatible extended module size is 110 mm x 155 mm. The extended module size is intended to support both larger processors and denser memory solutions over the smaller basic module size.
(Radisys White Paper, here )

You can find more technical specifications about COM Express from its sponsor, the PICMG, here . Be sure to look for the "COM" notation on their list of specifications, as they do not refer to it specifically as COM Express. There is also a nice white paper explaing COM Express vs. ETX from Kontron, here .

computers on module: other competing standards

Beyond COM Express, there are many other standards competing for attention in the crowded marketplace. Here are a few with some of the "sponsoring" vendors and links to more detailed coverage on the Internet, if available:

• ESMexpress® - championed by MEN Micro and VITA, a more ruggedized COM standard targeting industrial and other applications that are in harsh environments. Compatible with COM Express, the main focus is on the fanless cooling concept that is prepared for a power dissipation of up to 35 Watts and support of both conduction and convection cooling. To achieve this, the populated PCB is mounted into a frame and completely enclosed in an aluminum housing. (Details, here ).

• ETX - ETX, standing for Embedded Technology eXtended, is a highly integrated and compact (3.7 x 4.9 in.) (95 x 125 mm) computer-on-module (COM) form factor that can be used in a design application much like an integrated circuit component.

• QSeven - Qseven modules have a standardized form factor of 70mm x 70mm and have specified pinouts based on the high speed MXM system connector that has a standardized pinout regardless of the vendor. The Qseven module provides the functional requirements for an embedded application.

• nanoETXexpress Standard - nanoETXexpress is the standard compact COM solution created with the detailed requirement of customers designing for the fist-held, ultra mobile application space in mind - not only the COM Express™ pin-out Type 1 compatibility, but the 55 mm x 84 mm footprint as well.

• COMIT 1.0 Specification - COMIT stands for Computer On Module Interconnect Technology™ and is targeted towards small form factor COM processor modules and host baseboards leveraging the latest ultra-mobile and low power processor/chipset combinations. COMIT is the enabling technology to allow design of tiny processor modules to fit within the footprint of industry-standard, small form factor boards such as EBX, EPIC, PC/104, Pico ITX or other standard or custom-designed baseboards.

• EBX - EBX boasts highly flexible and adaptable system expansion, allowing easy and modular addition of functions not contained in standard product offerings. This EBX system expansion is based on popular existing industry standards — PC/104™, PCI, PC/104-Plus, PCI-104™, and PCMCIA.

In addition, several of the PC/104 vendors have actively promoted "stackable" standards. The most prominent of them is the Stackable USB championed by Micro/Sys, which uses the popular USB 2.0 connectors to mate CPUs and I/O boards. You can find out more, here .

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Express Logic develops, markets and supports the ThreadX® real-time operating system (RTOS), NetX™ TCP/IP networking stack, USBX™ USB stack, and FileX® embedded file system, and PrismX™ GUI toolkit for embedded applications. ThreadX is a royalty-free, full source code, small-footprint, low-overhead RTOS that is extremely easy to learn and use. ThreadX is one of the most widely deployed RTOS products in the world, with over 800 million products based on ThreadX.