In articles about industrial circuit boards, single-board computers (SBCs), and embedded control, the term "standard architecture" is frequently mentioned, specifically referring to the shape and physical dimensions of the product. However, in practical applications, precise terminology can be difficult to understand. Therefore, other interchangeable concepts are also used to describe the standard architecture of circuit board products, including: architecture, bus, footprint, layout, module, platform, protocol, specification, and standard. Generally, the length-to-width ratio in the standard architecture of industrial circuit boards is relatively small. Experts say that the square shape helps reduce board vibration and jitter, and this shape provides a more secure mounting. When the product exceeds the specified area, choosing different dimensions will bring other specific properties. A certain standard architecture defines the basic installation and functionality within the available space of the circuit board. Typical parts associated with the standard architecture of circuit boards include mechanical layout, connectors, and input/output (I/O) areas. Embedded control has special considerations regarding space, power supply, and reliability in the standard architecture of circuit boards. Regardless of what you call them, the application of standard architecture simplifies the work of developers. This also provides a certain guarantee for the long-term availability of products with common sizes and specifications for machinery manufacturers and their customers. Umbrella Simulation Method One method of classifying standard structures is to represent computer board standards using an umbrella-shaped view. Various elements of the board standard, such as mechanical dimensions, I/O performance, expansion interfaces with other boards, installation, and certain electrical parameters, are represented by sectors on the umbrella surface. This classification method was proposed by Robert Burckle, Vice President of WinSystems. "The area of ​​the sector represents the various elements of the standard structure," Burckle said. "Some specifications are more detailed because they describe power supply, I/O interfaces, installation locations of expansion connectors, prohibited areas, and other mechanical issues." Connectors, I/O ports, and even mounting holes are often considered as part of the standard structure. “Defining these standard structural elements can unify board products from different manufacturers, reducing difficulties that may arise when these products are mating cables, selecting enclosures, or integrating with other systems,” Burckle stated. “However, the concept of ‘standard structure’ does not include electrical characteristics, operating components, processors, and other chips that may be used.” General-purpose industrial computer board standards have specific functions, Burckle explained: “For example, VME and CompactPCI can be expanded into bus or motherboard systems; PC/104, EPIC, and EBX have self-storing I/O modules, so there is no need to mount them on a bracket or motherboard.” Derrick Lavado, product manager at embedded systems supplier Kontron North America, also agreed that the common attributes of standard structures for embedded and industrial boards should include the location of I/O ports, expansion ports, component height, and the location of mounting holes. “For a systems engineer, these attributes are essential considerations. They help design products with a more familiar architecture to users, reducing time to market. Simultaneously, this approach provides a pathway for product upgrades during technological innovation,” Lavado believes. Besides physical size, he considers I/O ports to be one of the most important attributes of standard architectures. For example, the installation locations of standard interconnect ports (LAN, parallel interfaces, USB, PS/2, etc.) are predetermined for PC/104, EBX, and other standard architectures. I/O interfaces are located in pre-defined, specific locations to enable further functionality. He also mentioned the component height limitations associated with some standard architectures. For instance, PC/104 uses a stackable expansion concept. Because I/O modules are often on the top layer of all stacked modules, with the CPU module at the bottom, the minimum clearance between each stacked module must be guaranteed; this also solves the overall system heat dissipation problem. Popularity = Lifespan “The most popular standard architectures often have the following characteristics: a high-performance CPU/chipset integrated within a small space,” Lavado continued. In his view, the PC/104 falls into this category. "The PC/104 module, when used with a compact enclosure, offers great installation flexibility. All I/O ports are routed from the board via cables, allowing the location of remote I/O to be flexibly changed according to design requirements." Today, typical PC/104 modules integrate CPUs and processors that boast powerful performance and low power consumption (such as Intel Pentium M and Celeron M). [align=center] Figure 1: The EPIC's size falls between the PC/104's stack format and the EBX's SBC format. [/align] At National Instruments, standard architecture refers to the physical dimensions and basic characteristics of the board. However, Tim Fountain, Hardware Product Strategy Manager at NI Instruments Control, suggests adding other factors such as mounting rails and connectors to this category. The installation location of interface connection devices is crucial for convenient and quick connections. NI places great emphasis on the long-term availability and reliable technical support of its board products in system applications, and on this basis, it tightly integrates the overall architecture and standards of the board with its standard architecture. Todd Walter, team manager for Industrial Measurement & Control, stated, “We prefer detailed and well-defined board standards that maximize product development support and clearly define the standard structure of the product.” Industrial systems require boards with long lifecycles, and related components must be available for an extended period. Walter further explained that NI considers standard structures from a higher, platform-level perspective, and their standard structures meet diverse customer requirements, such as thermal performance, low power consumption, vibration resistance, and resource versatility. NI's work involves various standard structures, including CompactPCI, PCI Express, and other PCI types. For example, PXI is a PCI expansion interface developed by NI specifically for instrumentation. NI provides timing, triggering, and synchronization signal functions for test and measurement applications using this type of PXI board. Similar to NI, WinSystems emphasizes the importance of standards and long-term product availability. Crucially, product design must be based on recognized standards and involve collaboration with multiple core suppliers to ensure long-term supply. “10- to 15-year lifecycles are not uncommon in industrial products and systems,” Burckle said. Standardized architectures also imply increased component interoperability and more efficient use of software tools. Regarding size and application , Ray Alderman, Managing Director of VITA (VMEbus International Trade Organization), a non-profit supplier/user organization dedicated to promoting VMEbus standards and open processing technologies, believes that the application of a product determines the choice of its standard architecture. The size of the board determines the number of connected devices that can be mounted on it. A very small form factor limits the possible number of I/O points. However, in simple industrial applications, such as injection molding controllers, a smaller form factor is sufficient because such controllers require relatively few I/O points, Alderman explains. As applications become increasingly event-driven, and with the demand for sophisticated interfaces for high-end applications, the number of I/O points required increases accordingly, such as in machine vision or motion control. Larger form factors can accommodate these requirements within their space and meet the needs of specialized applications. Currently, various standard architectures are involved in industrial applications; furthermore, more standard architectures will be developed over time. The following introduces several standard architectures frequently used in industrial or embedded control applications, all proposed by a specific association or organization. CompactPCI is an industrial bus standard based on the standard PCI (Peripheral Component Interconnect) specification; it comes in European standard card packaging and two basic sizes: 3U (100x160mm), which has a 220-pin connector; and 6U (233x160mm), which can be expanded to three 2mm pin connectors. CompactPCI cards are mounted at the front of the chassis, allowing I/O points to be routed from either the front or rear. The cards are vertically mounted, providing good heat dissipation; they also offer excellent vibration resistance. CompactPCI is designed for use in harsh environments—industrial automation, real-time machine control/data acquisition, instrumentation, and military systems, among others. CompactPCI was proposed by the Industrial Computer Manufacturers International (PICMG). This association has over 350 industrial computer product suppliers, ensuring customers receive long-term technical support from manufacturers. The EBX Embedded Board, eXpandable (EBX), is a 5.75" x 8.0" (146 x 203 mm) embedded board. This standard form factor is sufficient to accommodate a single-board computer (SBC) and its operating system. Simultaneously, the EBX board can be easily installed into the limited internal space of embedded application systems. Generally, the EBX board houses the CPU, memory, mass storage interface, display controller, parallel/serial interfaces, and other system components required by an embedded SBC. This standard form factor also provides users with various system expansion options using industry-standard modules, supporting stackable PC/104, PC/104-Plus, and PCI-104 specifications. This gives the EBX a large number of standard expansion interfaces. The board also has reserved I/O port areas and precisely specifies the locations of connectors and mounting holes. To standardize the layout of various interfaces and components, the entire EBX board is divided into 10 areas. The maximum allowable height of components in each area (A to J) varies from 0.5" to 1.5" respectively. Regional division serves as a guideline to enhance interoperability between products and packaging from different vendors. The EBX standard, developed by the PC/104 Embedded Systems Consortium, is currently at version 2.0. The EPIC Industrial Computer Embedded Platform (EPIC) is designed for applications where the standard EBX form factor is larger than required, while the standard PC/104 form factor is too small to accommodate the number of I/O interfaces and cabling requirements (see size comparison table for details). A key feature of this specification is that it provides more space for faster processors and a greater number of I/O interfaces required in industrial and other complex applications. EPIC can accommodate larger processors and their heatsinks and integrate functionality that would otherwise require multiple PC/104 modules into a single board. The EPIC standard format details the expansion slots (for the "104" specification), bus connections, and mounting hole locations on the motherboard and expansion boards. To standardize the placement of various interfaces and components, the standard structure also divides the board space into several distinct regions (see the region space table for details). Except for the "High Space Occupying CPU and Power Supply Region," the maximum height of components that can be installed in the other regions is specified. The "high-space-occupying CPU and power supply area" primarily houses the processor and its cooling fan or heatsink, as well as the power supply unit and power interface. EPIC also defines areas for three I/O ports, whose main function is to interface for matching connectors and cables that may be used between the "104 expansion board" and EPIC modules. The EPIC standard is also developed by the PC/104 Embedded Consortium, with its latest version being 2.0.5. More than 20 manufacturers are engaged in the production of EPIC boards, and this number is constantly increasing. PC / 104 is defined as a "small standard architecture that embeds the PC physical and electronic interface standard." According to the PC/104 Consortium, PC/104 was developed to address the user's requirement of embedding a microcomputer into the control of a product and system within a limited space. Another purpose of developing this standard architecture is to simplify board production and avoid the additional costs associated with customized products. PC/104 achieves structural, hardware, and software compatibility with the PC bus through stackable modules. These board modules come in two types: 8-bit and 16-bit, corresponding to the PC and PC/AT buses, respectively. PC/104 further specifies two bus options to alleviate the constraints of limited embedding space. These two buses are defined as "stack-through" and "non-stack-through," depending on whether the bus connection interface penetrates the module. An 8-bit module and a 16-bit module can coexist in a stack. It is said that approximately 160 multinational companies produce products based on the PC/104 standard. The latest version is 2.5. PXI is a modular measurement and automatic control instrumentation platform, primarily used in applications requiring a robust industrial standard architecture. According to the PXI Systems Alliance (PXISA), PXI combines the standard PC technology of CompactPCI with integrated timing triggering capabilities, resulting in performance improvements up to 10 times compared to older architectures. PXISA primarily focuses on the development and promotion of the PXI standard. National Instruments, Inc. extended CompactPCI technology to develop the PXI standard, therefore the standard architecture of PXI is consistent with that of CompactPCI. [align=center]Figure 2: EPIC provides three I/O areas (1A, 1B, 2, and 3) to connect I/O devices for different purposes. PC/104's expansion modules offer even more I/O options.[/align] As a standard with over 20 years of history, VME —the open industry standard architecture for embedded computers—still dominates in applications, particularly in military and defense applications. (VME is an abbreviation for "VersaModule Europa," although this technology has various names.) Originally initiated by VITA, VME established the framework for 8-bit, 16-bit, and 32-bit parallel bus computers, enabling the implementation of single-processor or multi-processor systems. VME's mechanical construction is primarily based on the IEC 60297 and IEEE 1101.1 standards, and is also known as the European standard card structure. VME boards come in two standardized forms: single-height (3U), mainly used in space-constrained and vibration-prone environments; and double-height (6U), which allows for the installation of more components when there is available space on the board. Eurocard Connections In fact, many popular industry standard structures, such as CompactPCI, PXI, and VME, are derived from Eurocard in their physical structure. The European standard card (Eurocard) mechanical standard (IEEE 1101.10) comprehensively specifies the modular dimensions of boards and patch panels; however, only a small number of these specified dimensions are implemented in products. Perhaps the most well-known are the 3U and 6U board sizes, where U refers to the panel height (1U equals 1.75 mm × 4.45 mm). The board height is smaller than the cable tray height to allow space for the board rails and panel. In practice, the height of a 3U board is 100 mm, while the height of a 6U board is 233.35 mm. Modular European standard cards start at a depth of 100 mm, with a 60 mm difference between each specified depth. While there are many standard specifications for board products, only a small number become stable, universal structures in actual industrial applications. Therefore, gaining user and market acceptance requires the test of time. The reputation for long-term product availability also needs to be verified over time.