High-speed, serial peripheral interfaces demand a new approach to module design. The COM (Computer On Module) Express standard meets those challenges. Supporting many popular new serial interface standards, including PCI Express, USB 2.0, ExpressCard, Serial ATA, and Gigabit Ethernet, it also retains the compact module size associated with its predecessor, ETX, handled by the ETX Industrial Group. PIGMG manages the new standard.
The ETX module standard brought a number of key features to the table. First was its compact stature, allowing it to mate with a low-profile motherboard. It mounted the connectors on the back of the module, leaving the top for densely packed processor and peripheral chips. There was sufficient headroom for SODIMM memory and even CompactFlash sockets. Best of all, a number of different vendors supported it, allowing a designer to easily choose the module required by an application. It also made it very easy to provide a solution that employed different performance modules for a range of products.
Migrating To New Serial Technologies
Embedded developers must embrace the high-speed serial technologies because existing and future sources of peripherals and peripheral controllers will utilize these serial links. Parallel bus technology like PCI and parallel ATA (Advanced Technology Attachment) will continue to exist, but it will get harder to obtain replacement parts of these types of peripherals in the future. Availability goes down while costs go up.
On the other hand, the availability of peripheral and peripheral interfaces supporting the new serial technologies like PCI Express, USB and Serial ATA (SATA) is going up while their cost is dropping rapidly. There is also the issue of better performance and functionality available with the new serial interfaces that embedded developers hope to get their hands on. For example, SATA support hot-swap drives making it possible to build systems with removable hard drives with not much more consideration that a non-removable drive. Likewise, fanout for USB and PCI Express is not really an issue. Technical limits exist but are rarely exceeded in any practical implementation. The standard will provide plenty of peripheral support without requiring hubs for expansion. They can easily be incorporated into a design should the need for more peripherals arise.
The new module standard will be more amenable to a variety of processor architectures because of the swift adoption of PCI Express into the processor and processor chip sets. This makes the form factor appealing to a wider range of developers than the original ETX format that had an x86 bias.