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COM Express™ Specification Overview
1.1
Concept of COM Express™
Computer On Module (COM) is off‑the‑shelf technology that has been in the embedded computer industry for years. A Computer On Module
integrates all the core components and standard I/O interfaces of a common PC onto an application specific carrier board. The key advantage
of the COM in the embedded computer industries is that all the highly integrated, high speed components such as CPU, chipsets and memory
are combined on a small module form factor for easy adaptation to different applications across multiple market segments.
COM Express™ modules have standardized form factors and have specified pinouts on the two system connectors that remain the same
regardless of the vendor. The COM Express™ module reflects the functional requirements for a wide range of embedded applications. These
functions include, but are not limited to, PCI Express, PCI, Graphics, High Definition Audio, parallel ATA, serial ATA, Gigabit Ethernet and USB
ports. Two ruggedized, shielded connectors provide the carrier board interface and carry all the I/O signals to and from the COM Express™
module.
Carrier board designers can utilize as little or as many of the I/O interfaces as deemed necessary. Therefore the carrier board can provide all
the interface connectors required to attach the system to the application specific peripherals. This versatility allows the designer to create a
dense and optimized package, which results in a more reliable product while simplifying system integration. Most importantly COM Express™
applications are scalable, which means once a product has been created there is the ability to diversify the product range through the use of
different performance class COM Express™ modules. Simply unplug one module and replace it with another ‑ no redesign is necessary.
1.2
Module Form Factors
The COM Express™ specification was developed by the PCI Industrial Computer Manufacturing Group (PICMG) in close collaboration with
many leading companies across the embedded industry in order to find an implementation solution to handle high speed serial I/Os, processors
and chipsets. COM Express™ 2.0 specifies three form factors, as well as seven different types of connector pinouts.
The three form factors are Compact, Basic and Extended.
With a form factor of 95x95mm and single (or two stacked) horizontal mount SO‑
DIMM,
the Compact module targets space-constrained mobile systems The Basic module footprint is 125mm x 95mm and focuses also on
space‑constrained, low power systems which typically contain one (or two stacked) horizontal mounted SO‑DIMM. The Extended footprint is
slightly larger at 155mm x 110mm and supports up to two full size DIMM (or mini DIMM) modules or two horizontal/vertical mount SO‑DIMMS to
accommodate larger memory configurations for high-performance CPUs, chipsets and multiprocessor systems. The placement of the shielded
220‑pin connectors and the mounting holes are identical between these form factors.
Note
The conga-CEVAL COM Express™ Type 2 evaluation carrier board can host either Compact or Basic form factor CPU modules.
