Compute Module 4: Carrier Boards & Industrial Use
What CM4 Is For
The Compute Module 4 is the Pi 4's guts on a SODIMM-style module, meant to be soldered or socketed onto a custom carrier board — not a general desktop replacement. It's the right tool when you're building a product or fixed industrial installation where you need a specific I/O layout, board size, or ruggedization that a standard Pi 4 board can't give you.
Variants Matter
- eMMC vs Lite: CM4 comes with 0/8/16/32GB onboard eMMC, or a "Lite" version with none (SD card or external storage only). Pick eMMC for anything that needs to survive vibration/power-loss without SD card corruption risk.
- WiFi vs no-WiFi: Non-wireless variants exist for RF-sensitive industrial environments or when you're adding your own certified radio module.
Carrier Board Options
- Official Raspberry Pi CM4 IO Board — full-size, breaks out everything (dual HDMI, both camera/display connectors, PCIe x1 slot, GPIO), meant for development and prototyping, not a final product form factor.
- Third-party carriers (Waveshare, DFRobot, etc.) — smaller footprints, application-specific I/O (industrial relays, RS-485, PoE, DIN-rail mounting).
- Design your own — CM4's pinout and mechanical spec are published; if you're doing a real product run, a custom carrier is where CM4 actually pays off vs just using a standard Pi 4.
Key Differences From a Standard Pi
- No USB-A ports, no full-size HDMI, no standard GPIO header — all of that is carrier-board dependent, defined by what traces the carrier breaks out.
- PCIe Gen 2 x1 lane exposed — real NVMe SSD support, or other PCIe peripherals, without the FPC-cable workaround Pi 5 needs.
- Two camera/display MIPI connectors instead of one — genuinely useful for stereo camera or dual-display industrial setups.
Flashing eMMC
eMMC modules flash over USB using rpiboot — put the CM4 in USB boot mode (jumper/switch on most carrier boards), connect via USB-C to a host PC, run rpiboot, and the module shows up as a mass storage device you can flash with the Pi Imager like an SD card.
When NOT to Use CM4
If you just need one or two units and standard Pi 4 form factor works fine, don't bother — CM4 + carrier board costs more and adds design complexity for no benefit at low volume. It earns its keep in embedded/product/industrial contexts where board size, I/O selection, or ruggedization actually matter.