A device is a term used mostly for hardware-related activities in a system, including disks, printers, graphics cards, and keyboards. When FreeBSD boots, the majority of the boot messages refer to devices being detected. A copy of the boot messages are saved to /var/run/dmesg.boot.

Each device has a device name and number. For example, ada0 is the first SATA hard drive, while kbd0 represents the keyboard.

Most devices in FreeBSD must be accessed through special files called device nodes, which are located in /dev.