42 Focus | Embedded computing tech PC/104 There are also other long-term, small form-factor board formats; notably, the 90 x 96 mm PC/104 that can be built into a stack with sensor and processor boards. This has been used for many years since being standardised in 1992, and while it may have been superseded in many areas by the COM Express specification, it still has key advantages; the primary one being that the PC/104 boards are more rugged and do not use a separate processor module that can have reliability issues. PC/104 embedded processing units (EPU) can be built from a CPU board, I/O board and integrated heat plate. The resulting unit has a footprint about half the size of equivalent single-board designs and is mechanically rugged with standard mounting-hole locations. The EPU concept simplifies the making of modifications to meet specific I/O needs. Existing products can be configured by modifying the I/O portion of the product, or, if greater modifications are required, a fully custom I/O board can be created for an existing board set. With the two-board concept, these modifications come at a lower cost and shorter lead time than other solutions. This approach also provides a processor upgrade path. Often, a newer CPU board can be paired with an existing I/O board to significantly upgrade a system, providing upgraded performance, memory capacity or extended product life without any I/O or cabling changes. For example, a new-generation CPU card can be added to an existing I/O card to boost the performance. For example, one company’s Owl EPU is a combination of a previous EPU I/O board and a new-generation CPU. Environmental testing means that EPUs are fully verified to operate in extreme environments, including the full industrial operating temperature range of -40 to 85 C and MIL-STD 202 conditions of shock and vibration. The mounting points, connectors and small crosssection of the PCBs limit board flex, and also provide excellent performance in high shock and vibration environments. One of the drawbacks, as with VNX, has been the lower performance of older standards. However, PC/104 has been updated with the faster PCI Express connectivity standard to support the latest processors and interfaces. This allows an EPU to use the mini PCIe or M.2 socket to add expansion modules or boards with almost no size penalty. Examples include additional Ethernet, video, GPIO and other I/O ports, as well as solid-state storage devices. PC/104 boards are using the latest Intel Xeon E 6 processors, the refresh of the Coffee Lake family with up to 32 GB of error-correcting memory, fast onboard NVMe SSD storage and TPM 2.0 security. The error-correcting memory makes it indispensable for mission-critical applications and aeronautics applications at higher altitudes. The board is aimed at intensive processing, particularly applications with security concerns or where limited communication bandwidth precludes sending raw data back to a data centre. Several built-in interfaces include 1 Gbit and 2.5 Gbit Ethernet, USB 3.1, serial ports, I2C, GPIO, analogue input/output (ADC/DAC) and Mini DisplayPort output. Onboard expansion includes one Mini PCIe slot and two M.2 slots, which can support functions such as 5G cellular, AI accelerators, GPS, flash data storage, analog and digital IO, additional data storage (SSD), display interfaces, wi-fi, Bluetooth and Ethernet. Modifications for the EPU include conformal coating, revision locks, December/January 2025 | Uncrewed Systems Technology A VNX+ module with the Nvidia Orin GPU (Image courtesy of Wolf Advanced Technology) PC104 vs COM Express form factors (Image courtesy of Versalogic)
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