COM-HPC vs COM Express

COM-HPC is a computer-on-module standard from PICMG for high-performance embedded computing, ratified in 2021, that puts the processor, memory and core logic on a plug-in module and connects it to an application-specific carrier board through two high-speed 400-pin connectors. It builds on the same two-board idea as COM Express, PICMG’s long-established module standard, but with far more PCIe lanes, faster networking and more power for current processors.

PICMG, the PCI Industrial Computer Manufacturers Group, is a non-profit consortium of companies that writes open standards for embedded and industrial computing, used widely in industrial and military and aerospace applications. In both of its module standards, the module houses the processor, memory and essential logic, and a carrier board tailored to the application brings out the I/O and subsystems. That split simplifies custom hardware and lets the processor and memory be upgraded by swapping the module, an approach COM Express has proved over two decades.

This guide compares COM-HPC and COM Express side by side: the module sizes and types, connectors, PCIe, networking, display and power, where each one fits, COM-HPC Mini, carrier board design, and how to decide whether to stay with COM Express or move to COM-HPC.

The table compares the two standards and their main variants. It shows the maximum each specification defines; what a particular module brings out depends on its processor, so always check the module datasheet. Sizes are given by their names in the specifications.

The power limits are PICMG’s figures for each COM-HPC size at the low end of its input range, before connector derating; most designs run well below them. COM-HPC modules take 12 V by default, with an optional 8–20 V input on Client and Mini. Our explainer on COM Express module types covers the COM Express pinouts in more detail, and our comparison of SMARC, Qseven, OSM and COM Express places both PICMG standards against the smaller SGET modules.

The two standards share an architecture but are built for different generations of processor. COM Express was designed when PCIe 2.0 and Gigabit Ethernet were the norm, and its connectors and power budget suit mid-power processors with integrated graphics. COM-HPC was designed for PCIe 5.0, 25 GbE, USB4 and processors that draw more power than COM Express can deliver or cool.

Put simply, COM Express offers moderate power, wide processor and vendor choice and a well-rounded I/O set with fewer PCIe lanes and lower-speed interfaces. COM-HPC offers more of everything at higher cost and power: more lanes, faster lanes, faster networking and the power for multi-core processors with high memory bandwidth. Our guide to PCIe generations explains why lane count and generation matter at this end of the range, and our explainer on PCIe 5.0 covers the newest generation.

No. PICMG continues to maintain COM Express, which gained PCIe 4.0 and USB4 options in revision 3.1, and module makers continue to release COM Express modules on new Intel and AMD processors. COM-HPC adds a tier above it for designs that COM Express cannot serve.

For most embedded and industrial applications that put power efficiency, cost and a broad choice of I/O ahead of peak performance, COM Express remains the obvious choice. It suits industrial automation, military, aerospace and transport systems where COM-HPC’s extra capability would be more than the job needs, and its wide adoption, broad vendor support and long field record make it the standard most module designs start from. COM-HPC earns its place when the processor, memory bandwidth or I/O needed simply will not fit through a COM Express connector.

COM Express modules are defined by a type, which fixes the pinout, and a size, which fixes the outline. A module and carrier must share the type; the size sets the room for the processor, memory and cooling.

Older Type 2 modules still appear in long-running designs, but new carriers use Type 6, 7 or 10. Size names run from Mini through Compact and Basic to Extended, and a carrier can be made to fit its enclosure exactly. Our COM Express SBCs pair a module with a matching carrier and heat spreader, and our COM Express carrier boards are supplied bare or with the module fitted, imaged and validated.

Since COM Express was introduced, it has become a staple of industrial automation and control. These applications need dependable, long-lasting components with balanced processing power and versatile I/O, and COM Express combines energy efficiency with the processing a wide range of automation tasks need. One example from our projects: a COM Express SBC on board reverse vending machines scans plastic, glass and aluminium for crushing and sorting.

A key strength is ruggedness under shock and vibration. COM Express carrier boards can be made to the exact size of the enclosure, with I/O connectors soldered directly to the carrier so there is no internal cabling to work loose. Mating the module with a heat spreader lets the system cool by conduction through the enclosure, so low-power processors can run fanless, as our guide to active vs passive cooling explains, which suits aerospace and military systems where size, weight, power and cost, often abbreviated SWaP-C, are tightly budgeted.

COM Express is also common in mission computers, where connector reliability is critical. These designs often use breakout boards that route I/O to MIL-DTL-38999 or MIL-DTL-5015 circular connectors, known for holding signal integrity and staying mated under extreme vibration and shock. Removing loose internal cables improves reliability and makes maintenance in the field simpler. COM Express also sits inside stackable systems: PC/104 single board computers such as the Diamond Systems Athena IV put the processor on a replaceable COM Express Mini module, so the board shape and connectors can outlive the processor.

COM-HPC defines two main pinouts. Client modules carry desktop and mobile processors with graphics, for systems that need displays and plenty of PCIe. Server modules carry high-core-count processors with many memory channels and fast networking, usually without graphics, for edge servers and data processing.

In data centres and at the edge, COM-HPC Server’s ability to carry high core-count processors, large memory and extensive I/O suits dense data processing and compact, efficient servers. Server modules often include a baseboard management controller for remote power control and monitoring, the same function our rack mount servers rely on. Our guide to AMD EPYC Embedded covers one of the processor families that reach this class.

COM-HPC Mini is the compact COM-HPC size, added in revision 1.2 of the specification. It uses a single 400-pin connector, soldered memory and a low overall height, and it sits in size between COM Express Mini and COM Express Compact. That makes it a high-bandwidth option for rugged, space-constrained systems that would previously have used a Type 10 or a small Type 6 module.

“With a form factor sitting between the original COM Express Mini and COM Express Compact, we expect to see COM-HPC Mini play a significant role in rugged edge computing where compact size, high performance and low power consumption are essential. Its small size suits space-constrained installations, while its support for high-performance processors and high-bandwidth memory lets it handle complex workloads such as AI inference at the edge.” Andrew Whitehouse, Managing Director, Things Embedded

When an application needs more than even a high-end COM Express module can deliver, COM-HPC is the module standard to look at, for its processing power, data throughput and connectivity.

Our edge AI computers show the GPU-equipped systems this class of module competes with. In each case the alternative is usually a full motherboard or a rack server, so COM-HPC is chosen when the project also needs the module approach: a custom carrier for the I/O and enclosure, and a processor upgrade later without a new carrier. Our guide to choosing an embedded motherboard covers the motherboard route.

The carrier board carries the risk in any module-based design, and COM-HPC raises the stakes. PCIe 5.0 runs at 32 GT/s, so trace lengths, materials, vias and connector placement all need more care than on a COM Express carrier, and long runs to slots or cables may need retimers. PICMG publishes a carrier design guide for each standard, and module makers publish reference carriers that are a sensible starting point.

A module and carrier can also be bought as a matched pair, which is how our carrier boards are often supplied. For processors that change faster than the product, our guides to the system on module and the system on chip explain why the module boundary sits where it does.

For an existing COM Express product, the default is to stay: a new module on the same carrier is the cheapest upgrade, and COM Express modules continue to appear on current Intel and AMD processors. Move to COM-HPC when a requirement simply will not fit.

Lifecycle points the same way. A COM Express design can draw on many module makers and a long record of second sources, while the range of COM-HPC modules and carriers is younger but growing. Either way, choose modules with published availability and plan the next module before the current one reaches end of life, as covered in our guide to embedded processors.

We stock COM Express Type 6 and Type 10 carriers, supplied bare or preassembled with the module fitted, imaged and validated, and complete COM Express SBCs. We do not currently stock COM-HPC hardware; where an application needs it, we can advise on the platform and source it as part of a build.