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For a realistic do-it-yourself x86 computer-on-module project, design the application-specific carrier board around a compatible COM Express module; do not treat the project as designing the processor module itself. The module supplies the processor, memory and core logic, while the carrier adds the connectors, power circuitry and peripherals your system needs. “BIOS-based” needs care: modern x86 platform firmware is not necessarily a traditional PC BIOS, and the correct boot and flash design depends on the exact module.
What you are building
COM Express is a two-board architecture: a compute module plugs into a custom carrier board through a high-pin-count connector. The module/carrier boundary is the key compatibility point. The module implements the processor and core platform; your carrier adapts the module’s supported signals to the system’s power input, displays, storage, networking, USB devices, expansion and enclosure.
That split makes a custom system more manageable than designing a processor board from scratch, but it does not make every module interchangeable. A carrier must match the selected module’s size, pinout, electrical requirements, supported interfaces, mechanics and firmware expectations.
Choose the standard, size and module together
PICMG’s COM Express materials describe four module size classes. The class name alone does not tell you the dimensions or whether a particular module exposes every interface you want; confirm both in the applicable specification and the module’s mechanical drawing and documentation.
#1 Best Overall
| Module size class | What the available material establishes | What to verify before layout |
|---|---|---|
| Mini | A COM Express module size defined by PICMG. | Exact dimensions, connector placement and mechanical clearances in the applicable specification and module drawing. |
| Compact | A COM Express module size defined by PICMG. | Exact dimensions, connector placement and mechanical clearances in the applicable specification and module drawing. |
| Basic | A COM Express module size defined by PICMG. | Exact dimensions, connector placement and mechanical clearances in the applicable specification and module drawing. |
| Extended | A COM Express module size defined by PICMG. | Exact dimensions, connector placement and mechanical clearances in the applicable specification and module drawing. |
PICMG says Base Specification Rev. 3.1 was released in summer 2022. Its page described Rev. 3.2 as in progress and not ratified when checked; standards status can change, so confirm the current revision and obtain the full applicable specification before making compliance-sensitive design decisions. Rev. 3.1 added or updated support for PCIe Gen 4, SATA Gen 3 and USB4, and lists optional MIPI-CSI and SoundWire support as well as an updated connector list including 16 Gbps versions. Those are standard-level capabilities, not guarantees that a given module implements them.
Select the pinout type and module by matching the required signals to the specific vendor implementation. Do not infer that an interface is present simply from a type number or the standard’s feature list. Ask the module vendor for the data sheet, carrier design recommendations, power-sequencing details, mechanical drawing, and BIOS or firmware configuration and recovery documentation before freezing the carrier design.
Rank #2
- 【Compact Design】Same size as the Compute Module 5, this expansion board is ideal for narrow application environments and end-product integration, featuring a CM5 socket compatible with all CM5 variants.
- 【High-Speed Connectivity】Equipped with USB 3.2 Gen1 port, Gigabit Ethernet (RJ45) with IEEE1588 support, and a PCIe Gen 2 x1 interface for connecting various adapter boards and modules.
- 【Rich Multimedia Interfaces】Supports 4K output via Mini HDMI port, dual MIPI interfaces for DSI displays or CSI cameras, and a 3.5mm audio jack for clear sound output.
- 【Flexible Storage and Memory Options】Compatible with CM5 modules offering 2GB to 16GB RAM and 0GB (Lite) to 64GB eMMC flash, with faster data rates up to 200 Mbps for efficient performance.
- 【User-Friendly Features】Includes BOOT and power buttons, a 40-pin GPIO header for HAT modules, a PWM fan header for cooling, and a dual-color LED for power and status indication.Available with pre-soldered header (CM5-NANO-B-M version).
Compare candidates against the actual application
- Mechanical fit: module size, connector placement, mounting, enclosure and service access.
- I/O: required displays, PCIe links, USB, storage, networking, camera, audio and management signals, checked against the module pinout.
- Performance and thermal design: workload, module-specific power documentation, cooling method and enclosure conditions. A rating for one product is not a universal COM Express limit.
- Firmware and support: documented boot-storage arrangement, initialization dependencies, update and recovery path, vendor support and lifecycle.
- Evaluation compatibility: whether a reference carrier or development kit supports the target module and has the connectors and power capability your prototype needs.
As examples of product-specific power descriptions, ADLINK describes some of its Type 6 Basic offerings as reaching up to 75 W and its Compact examples as 5–20 W. These figures characterize those vendor product classes, not limits or typical values for all COM Express modules. Use the exact candidate’s documentation for power budgeting and cooling.
Design the carrier in a controlled sequence
- Write down system requirements. Specify enclosure and dimensions, operating environment, workload, displays, network links, storage, USB and expansion needs, management, service access and intended production conditions.
- Choose a specific module, not just a standard. Check that its size, pinout, interfaces, power and thermal characteristics satisfy those requirements. Obtain the vendor’s design and firmware documents before committing to a board.
- Build an interface matrix. For each required function, record the module signal or interface, its electrical and routing requirements, the carrier circuitry or connector, and the source document that confirms support. Mark unused signals deliberately. Resolve discrepancies between the standard and module documentation with the vendor.
- Plan power, reset and boot control. Implement the power input and sequencing, reset behavior, boot controls and other required carrier functions according to the selected module’s documentation. Do not copy an old example circuit without verifying that the signal names, electrical levels and behavior still apply.
- Design the application-specific circuits. Add the connectors and circuitry for the chosen displays, storage, peripherals and expansion. Review high-speed routing against the actual link rates and layout rules in the current specification and module design recommendations; the connector carries many high-speed signals, so pin mapping alone is not a routing plan.
- Check mechanical and thermal integration. Use the module drawing and carrier guidance to place the connector, mounts and cooling provisions. Validate the design against the intended enclosure and operating environment rather than assuming another module’s thermal solution will fit.
- Prototype and validate. Where possible, first evaluate the module on a compatible reference carrier or development kit. On the custom carrier, validate power-up and reset, firmware and memory behavior, peripheral enumeration, thermals and signal integrity with an appropriate lab process before treating the design as production-ready.
What “BIOS” means on a COM Express design
In this context, “BIOS” may mean traditional legacy PC BIOS behavior, or it may be shorthand for platform firmware that initializes hardware and boots an operating system. Do not assume that the carrier-board designer can create a complete production firmware image from a generic recipe. Initialization may depend on processor and chipset programming information, vendor-provided binaries, board-specific configuration and module-vendor support.
Rank #3
- Used Book in Good Condition
Intel Firmware Support Package (FSP) is one possible dependency for Intel-based firmware work, not a general requirement for every x86 module. Intel’s FSP v2.2 External Architecture Specification, dated May 2020, describes FSP as a binary distribution of silicon-initialization code and cautions that some programming information is proprietary or may require legal agreements. Confirm the applicable vendor, version, access terms and integration requirements for the exact platform.
Do not copy the legacy carrier Firmware Hub circuit as a current recipe
PICMG’s Carrier Board Design Guide Rev. 2.0, dated December 6, 2013, includes an LPC Firmware Hub example in an appendix titled “Deprecated Features.” In that illustrated arrangement, pulling BIOS_DISABLE# low disables the module BIOS and permits BIOS on a carrier LPC or PCI bus; the example uses an older PLCC Firmware Hub device. This documents a historical option, not a current recommendation for a new design.
Rank #4
- Stretchable tie-down straps secure different size surfboards and stand-up paddleboards to vehicle roof for safe transportation
- Looped ends fasten around the vehicle load bars
- Webbing is strong and UV resistant
- Simple and easy to use cinching system keeps board stable during transit
- Prod Dims: 1.0"H x 60.0"L x 1.5"W; 0.45lb
Boot storage and firmware-selection arrangements can differ between modules. Before adding carrier flash or BIOS-selection circuitry, verify the current applicable specification and the exact module manual for boot topology, straps, signal voltage levels, approved firmware configuration, update method and recovery procedure. If a tutorial or schematic does not identify those details for a specific module, it is not enough to design that circuit safely.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Use a reference carrier to reduce prototype risk
A COM Express Type 6 development kit or reference carrier can help evaluate a module and prototype the carrier interface before a custom board is ready. ADLINK lists Type 6 reference carriers and development kits, including generation-specific examples. Treat these as evaluation options, not universal fixtures: confirm that the exact kit supports the selected module, specification revision, connectors and power requirements. A kit that demonstrates one module does not establish compatibility with another.
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A concrete schematic, bill of materials, BIOS-storage topology, power budget or compliance plan cannot be specified without a target module and system definition. At minimum, settle the following first:
- Exact module SKU and its vendor documentation.
- Required interfaces and connectors, plus the selected COM Express size and pinout.
- Power source, module-specific power and sequencing requirements, cooling approach and operating environment.
- Enclosure, mounting and service constraints.
- Firmware configuration, silicon-initialization dependencies, update and recovery path.
- Production and regulatory requirements for the intended market.
PICMG’s Carrier Board Design Guide adds implementation detail but does not replace the full specification. Because Rev. 2.0 dates to 2013, use it alongside the current applicable specification and the selected module’s manuals, and treat legacy examples as historical unless current documentation confirms them.
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