The original COM module

Paul Boughton

PC/104 is well-known as a rugged, stackable PC. Its modular design allows it to be easily adapted to many applications and makes field repairs and upgrades simple, writes Jim Blazer.

What could be simpler than a computer where one can pick and choose boards from many suppliers and have confidence that everything will work together nicely?  

With PC/104, designers can build a stack as tall or as short as necessary to get the features needed, knowing that the design is not 'boxed in' if new functionality is later required. Systems can use standbys like ISA and PCI bus or take advantage PCI Express, the latest bus technology.

But did you ever think about using PC/104 as a COM module?  PC/104 was the original COM module adopted as an open standard in March 1992 by the PC/104 Consortium. Its small size coupled with standard bus connectors makes it a perfect mezzanine module to a larger motherboard. CPU development is expensive and risky. If you choose one of the many PC/104 CPUs on the market, you will have ISA, PCI, USB, or PCI Express bus expansion with a broad selection of power and performance. The newly approved PCIe/104 Type 2 adds USB 3.0, SATA, and LPC connectivity.
What if one needs Ethernet, serial I/O, digital I/O, or some other function? Many CPUs have these features and one can cable directly to the CPU for these functions or even have the I/O connectors made to stack to the motherboard for virtually unlimited 'User I/O'.

Already building a custom CPU on your motherboard but worried that you will be asked to put an Ethernet switch, CAN controller, or opto-isolated I/O later? Put a PC/104, PCI-104, or PCIe/104 bus on the motherboard and your ability to expand the system just became limitless. If you cannot find the expansion module you need from the many already on the market, you can build one for your specific application.  

Jim Blazer is with RTD Embedded Technologies Inc. For more information, visit