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Chip, module, SoM, dev board, SBC

The same processor is sold as a bare chip, a module or a ready-made board. Their prices are not comparable, and mixing them up is a common mistake.

Foundation

Read firstMicrocontroller or microprocessor?
The same processor as a bare chip, a system-on-module and a complete board A bare application processor is the silicon alone and needs DRAM, boot storage, power parts, a crystal, a reset circuit and a multi-layer board around it. A system-on-module adds DRAM, storage and power management and plugs onto your carrier board. A development board or single-board computer is complete, with nothing to design. A pre-certified radio module packages a wireless chip with its RF circuitry. Bare application processor Chip the silicon alone You still add External DRAM Boot storage A PMIC or regulators A crystal, a reset circuit A multi-layer PCB DDR routing with length-matched traces System-on-module (SoM) Chip DRAM Storage Power management You still add Your own carrier board and what it carries, which the module plugs or solders onto No DDR routing of your own: that is done on the module Dev board or SBC Chip Complete boots on a desk You still add Nothing to design: it is complete and boots on a desk Pre-certified radio module Wireless chip RF circuitry In the US and some other markets, a product can reuse the module's radio approval, but only with the antennas and conditions in that approval, and only where the module is approved. The product still needs its own tests, such as emissions.
A bare application processor still needs DRAM, storage, power parts and a carefully routed board; a system-on-module adds the first three, and a dev board or SBC is complete.

Key points

  1. A bare chip is the silicon alone. A system-on-module (SoM) adds DRAM, storage and power management on a small board that plugs or solders onto your carrier board. A development board or single-board computer (SBC) is complete and boots on a desk.1
  2. An application processor cannot run alone: a product also needs external DRAM, boot storage, a PMIC or regulators, a crystal, a reset circuit and a multi-layer PCB (one vendor's guide recommends at least eight layers for its part).21
  3. Routing external DDR memory demands controlled-impedance, length-matched traces on a multi-layer board. Vendors publish dedicated DDR layout guidelines, and buying a SoM is one way to avoid doing this routing yourself.2
  4. A pre-certified radio module packages a wireless chip with its RF circuitry. In the US and some other markets, a product can reuse the module's radio approval, but only with the antennas and conditions in that approval, and only where the module is approved. The product still needs its own tests, such as emissions.34

Common mistakes

  • Comparing a bare chip's price with a dev board's price. They are different products.

Where to go next

Sources

  1. Raspberry Pi Compute Module 5 datasheet · Raspberry Pi · Datasheet
  2. i.MX 8M Mini Hardware Developer's Guide (IMX8MMHDG) Rev. 4.1 · NXP · Reference
  3. KDB 996369 D04 Modular Transmitter Integration Guide: Guidance for Host Product Manufacturers (public draft review copy, April 2020) · US FCC Office of Engineering and Technology · Regulation
  4. Espressif certificates · Espressif · Vendor page