What Is a System-on-Module (SoM)?

A system-on-module (SoM) is a complete computing core, with the processor, memory, storage and power management built onto one small board, that plugs into a second board called a carrier. The carrier supplies the connectors, expansion slots, sensor interfaces and mechanical fit that the product needs; the module supplies the compute. Separating the two lets a product keep its carrier design while the module underneath is upgraded, replaced or scaled.

The same idea goes by several names. PICMG calls it a computer-on-module (CoM), which is where the COM Express and COM-HPC standards get their names. NVIDIA calls its Jetson products modules, and the boards they plug into Jetson carrier boards. Raspberry Pi calls its version a compute module. In every case the principle is identical: the hard, high-speed, short-lifecycle engineering lives on the module, and the application-specific engineering lives on the carrier.

The split is consistent across every standard. The module carries the parts that are hardest to lay out and that change most often: the processor or system-on-chip, DRAM (usually soldered), boot storage such as eMMC or NVMe, the power sequencing the processor demands, and often the Wi-Fi or trusted platform module. High-speed signals such as PCIe, USB 3, display and Ethernet are routed to the module connector but not to any physical port.

The carrier board turns those signals into a product. It decides which of the available PCIe lanes become an M.2 slot, a MiniCard socket or a 10 GbE controller; which USB lines reach a locking connector on the front panel; whether the display output is HDMI, DisplayPort or an embedded panel; and what the board looks like mechanically. It also carries the parts the module does not: the DC input stage and any wide-range or isolated power, serial ports, CAN bus, digital and analog I/O, camera connectors, ignition control and the mounting holes that match the enclosure.

That is why two products on the same module can look nothing alike. A Jetson Orin NX on a 3.5-inch industrial carrier with dual Gigabit Ethernet and CAN is a machine controller; the same module on a carrier with four GMSL camera inputs is a perception computer. The compute is identical, the carrier is the difference.

The vocabulary overlaps, so it helps to pin it down. System-on-module and computer-on-module mean the same thing; SoM is the generic term and CoM is the PICMG term used by the COM Express and COM-HPC standards. A system-on-chip (SoC) is the silicon itself, the single package that holds the CPU cores, graphics and I/O controllers, and is what sits at the centre of the module. A single board computer (SBC) is a complete computer on one board, with the processor, memory and all the I/O connectors together, and no module to remove.

There is a grey area worth knowing. Several rugged board makers sell a carrier with the module already fitted and call the result a COM-based SBC. Functionally it is used like an SBC, but because the module can be changed it keeps the lifecycle advantage of a modular design. Our COM Express carrier boards are sold both ways: bare, for customers fitting their own module, and preassembled with the Intel module, heat spreader and storage in place.

For more on the chip at the centre of every module, how a system-on-chip combines CPU, graphics and I/O on one die explains the trade-offs against a discrete design.

The strongest reason is lifecycle. Embedded processors are typically available for seven to fifteen years, but the products built on them often have to be supported for longer, and the requirement to add performance usually arrives well before the end of that window. With a module-based design the carrier, the enclosure, the cabling and the certification evidence stay as they are; the module is swapped for a newer one on the same connector and the software is revalidated. Rugged board makers have kept products in production for well over a decade this way.

The second reason is scalability. Most standards allow a range of modules on one carrier, from a low-power part to a high-performance one, so a single product design can be offered at several price and performance points. A Type 6 carrier might ship with an Intel Atom module for a basic configuration and a Core or Xeon module for the high-end one; a Jetson carrier designed for Orin NX also takes Orin Nano.

The third is time and risk. Laying out DDR5 memory and PCIe Gen 4 to a modern processor is exacting, multilayer work with a long validation cycle. Buying that as a finished, tested module lets the product team spend its engineering time on the carrier, which is comparatively simple, and lets a custom carrier be turned around in months rather than the year a full board design can take.

Finally there is the supply argument. Because the module is a standard part with several sources, a carrier designed to COM Express or SMARC is not tied to one vendor’s roadmap. Jetson is the exception here: it is single-source, and buyers accept that for the AI performance and software stack it brings.

A module is not automatically the right answer. If the product has one fixed configuration, a standard form factor such as Mini-ITX or 3.5-inch already fits the enclosure, and the lifecycle requirement is covered by the board maker’s own long-life program, then a single board computer is simpler to buy, simpler to cool and usually cheaper at the volumes most industrial products run at. There is no connector between the processor and the I/O, which also removes one source of vibration-related faults.

The trade-off is what happens when the processor changes or the I/O has to. On an SBC that is a new board. Teams that expect either to happen inside the product’s life, or that need an I/O set no standard board offers, are the ones a module-based design pays back.

Environment. Where does it run and how is it powered? Wide-temperature operation, conformal coating, shock and vibration, and a vehicle or MIL-STD power input all belong on the carrier and the module has to be rated to match. Latching connectors and a heat spreader that mates to the enclosure matter more in a vehicle than in a cabinet.

Performance. Is the workload general-purpose x86, or AI inference? An Intel Core or Xeon module on a Type 6 carrier suits control, data acquisition and machine vision with conventional software; a Jetson carrier board and module suits neural-network inference on camera and sensor data. Memory, storage and the number of PCIe lanes available to the carrier follow from that choice.

Expansion. Which interfaces does the product need on day one, and which might it need later? PC/104 and PCIe/104 stacking, MiniCard and M.2 sockets, camera inputs and isolated I/O are carrier decisions. A carrier with a spare expansion socket is often what turns a two-year product into a ten-year one.

Lifecycle. How long must it be supportable, and who supports it? Ask for the module and carrier availability commitments in writing, confirm that a newer module on the same standard is on the roadmap, and plan the software so a module swap is a revalidation rather than a rewrite.

A module and a carrier are parts, and a parts list is not a product. Things Embedded supplies Jetson and COM Express carrier boards as working platforms: we recommend the module and carrier to start from, fit and image them, validate thermals and I/O in the target enclosure, and support the result through its life. Where no standard carrier fits the requirement, we design a custom one; a fanless GPU computer built on a custom Jetson carrier board is a recent example.

If you are weighing up the two x86 standards, our comparison of COM-HPC and COM Express sets out where each one fits. If the workload is edge AI, start with our guide to choosing a Jetson carrier board, and note that Jetson Thor needs its own Thor carrier board rather than an Orin one.