It can be argued that small form factor design trends are paradoxical. As form factor size decreases, functionality requirements increase; as processing power requirements heighten, lower power consumption and thermal output is expected. Add to that the requirement for ruggedness to accommodate for the shock, vibration, humidity, and temperature extremes and variance inherent in mobile and outdoor applications, and designers are faced with a very complex soup.

Figure 1. The PC/104 embedded computing format has no backplane, instead allowing modules to stack together like building blocks. Many applications in defense and transportation still incorporate legacy devices that require an ISA-BUS interface.
Mobility and environmental extremes are critical considerations for rugged board design in military, transportation, industrial and surveillance applications, to name a few. And with today’s emphasis on SWaP(-C) in embedded system design, it’s critical for embedded designers to follow industry standards, and equally critical for industry standards to continue evolving to maintain relevance.

Selecting the Right Form Factor

Embedded Board eXpandable (EBX) and PC/104 are good format options for designs that can handle slightly larger Single Board Computer (SBC) form factors. With just 46 square inches of surface area (8" × 5.75"), EBX balances size and functionality with a bolt-down SBC format supporting rugged embedded designs with higher-performance Central Processing Units (CPUs), such as those using multi-core technology for networking, digital signal processing (DSP), and graphicsheavy applications, and generous onboard Input/Output (I/O) functions to support everything from large data exchange to video. The PC/104 embedded computing format has no backplane, allowing modules to stack together like building blocks more rugged than typical bus connections in PCs (such as PCI or PCI Express slot cards).

PC/104 delivers high performance combined with low power, stackable configurations and adherence to MIL-STD, and it meets key industrial and transportation standards for electromagnetic interface/compatibility (EMI/EMC), e.g. EN50121, EN50155, EN610000-x, etc. The ability to build stacks of PC/104 modules creates opportunities for developing a diversity of complex, often mobile, applications that range across industrial, transportation, and defense environments where PC/104’s robust and reliable capabilities are required. In addition, PC/104’s transition into vision and visual security monitoring systems is benefitted by PCI Express, as it has the capacity to directly meet the bandwidth needed to support multiple data streams (Figure 1).

Though the number of stacks included in PC/104 systems has been decreasing, the form factor continues its warm relationship with industries requiring rugged applications with high resistance to shock and vibration. In defense and transportation, legacy devices and ISA-BUS interface requirements are still plentiful. With high-speed serial I/O interfaces, such as PCI Express, supported in current PC/104-based standards, PC/104 boards are keeping pace with the movement toward consolidating workload on expansion modules, requiring fewer layers to fulfill application requirements.

The ability to withstand temperature extremes often associated with remote environments still allows PC/104 to excel in off-grid computing (e.g., defense apps). Stackable, mix-and-match modularity and the intrinsically rugged design of PC/104 is ideal for many of today’s technology upgrade programs looking for Commercial Off-the-Shelf (COTS) options — especially those that value SWaP(-C). In addition to ruggedness, users of PC/104 have come to expect long lifecycle support. When considering shrinking DoD budgets, the robustness, longevity and compatibility of the PC/104 ecosystem ensure strong system support and minimized costs.

Figure 2. A design using the COM Express form factor provides off-the-shelf functionality and an easy upgrade path by putting the customization on the baseboard, thereby creating more flexibility with the module without sacrificing performance.
While PC/104 allows flexibility by combining cards to meet application requirements, the PC/104 format becomes less attractive when very high computing speed and network throughput is required — situations where VPX or CompactPCI (cPCI) formats are better suited. In cases where an application design requires very specific I/O or physical size/shape restrictions, then a Computer-on-Module (COM) approach would provide better results.

COMs are complete embedded computers built on a single circuit board for use in small or specialized applications requiring low power consumption or small physical size. Though they are compact (ETX/XTX at 114mm x 95mm and COM Express at 125mm x 95mm to 84mm x 55mm) and highly integrated, COMs can accommodate complex CPUs (Figure 2).

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