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