Kishan Jainandunsing
(February 2006)

In this column we explain the COM Express specification in a series of tutorials, starting this month with Part I. Part I gives an introduction to the specification.

Introduction to the COM Express Specification

The Definition of COM

COM stands for Computer-On-Module. A COM is defined as a module that integrates and packages all necessary functions of a bootable host subsystem in a single component. This component or module, has a connector interface for power and all other signals normally found on a motherboard, such as IDE, PCI bus, LPC bus, USB, etc. A carrier board or main board is supplies power to the module and brings out the signals from the module’s connector interface to expansion sockets, such as PCI slots, I/O chips, such as IEEE1394, and other devices, such as FPGAs and DSPs. This methodology effectively reverses the concept of the single board computer, where application specific functionality is added through (PCI) add-on cards. Figure 1 below illustrates this reversal.

Figure 1. COM-based SBC versus traditional SBC.

COM Benefits

The COM methodology has powerful benefits for OEMs. These include:

• Control over form factors.
• Fast time-to-market.
• Lower cost.
• Scalability.
• Design reuse.

Control over form factors means that portable and handheld form factors are feasible, unlike with the traditional approach with off-the-shelf SBCs. Indeed, these SBCs are either designed for back plane, desktop or luggable applications and one would be hard pressed to get them to work for a handheld or mobile application.

Fast time-to-market is a distinct benefit where a traditional off-the-shelf SBC form factor does not work. In this case only the carrier board has to be designed, as opposed to the complete motherboard with the CPU and chipset. OEMs can keep designs in-house, closest to the markets they serve, thus being able to react faster to changing market needs.

Lower cost comes into play where the carrier board can be kept very low in complexity and limited to a 4 or 6 layer PCB. In case of a single board solution the entire board would be a 14 to 16 layer PCB and consequently be higher in cost.

Scalability is a consequence of the fact that all variations in terms of chipsets and CPU are contained in the module, whereas all interfaces with the module are static. Again, when comparing this to traditional off-the-shelf SBCs, the latter needs to be replaced when the chipset goes obsolete or if the product is required to keep up with chipset and COPU advances. And, as is often the case with off-the-shelf SBCs, connectors, cable headers, etc. are seldom in the exact position as on the board that is being replaced.

Design reuse is most pronounced in cases where the product comes in several variants, such as a floor, bench top, portable, mobile or handheld model. In such cases, the same design for the carrier board is spun in different form factors and with some functionality deleted or added.

The Origins of COM Express

The COM methodology has become widely popular in the embedded industry. OEMs have realized the benefits of the COM methodology. Consequently, many incompatible COM products have been introduced in less than a decade. This lead to fragmentation of the market and limited growth of COM shipments.

PCI Express and Serial ATA provided the opportunity to start afresh and address the fragmentation through the introduction of a single, widely adopted, industry standard. Hence, the COM Express specification was created by the PCI Industrial Computer Manufacturing Group (PICMG), an open industry consortium that produces specifications for embedded computer systems, such as CompactPCI and AdvancedTCA.

Markets and Applications

The markets and applications targeted by the COM Express specification include, but are not limited to the following:

• Healthcare. Examples include portable ultrasound machines, patient monitoring equipment and meds robots.
• Industrial automation. Examples include machine-imaging systems and process monitoring & control panel computers.
• Gaming and entertainment. Examples include casino slot machines, digital casino table games and video arcade machines.
• Test & measurement. Examples include HD video broadcast network analyzers and high-speed protocol analyzers.
• Advertising and retail. Examples include digital billboards, kiosks, POS and ATM terminals.
• Network storage and security. Examples include NAS, storage virtualization and VPN.
• Telecom. Examples include VoIP PBXs.
• Defense and security. Examples include wearable special ops computers, command control, communications, computing, intelligence, surveillance and reconnaissance (C4ISR) computers and portable detectors for hazardous substances.

According to a 2005 VDC study, the market for COM products will show a 31% CAGR until 2008 with respect to legacy product categories, such as PC/104+, SBCs, etc.

End of Part I