For most BBB/BBW users, the boot process ends when their application is running. However, from a support point of view, there is an earlier dividing line. What happens after the bootloader (U-Boot) has finished is often a different support process than what happens during and before the bootloader runs. The bootloader and the earlier messages are typically only visible through the debug serial port, whereas Linux messages can be accessed via USB or the Ethernet using SSH.

For most users, the bootloader starts Linux. How Linux gets started depends entirely on the bootloader configuration. For the BBB, the bootloader will load the kernel and other Linux support pieces from the microSD card (if present); failing that, it will fall back to the internal flash. For advanced Linux development such as kernel development, the kernel does not usually need to be updated on the internal eMMC flash. A microSD card can be prepared and the bootloader will load Linux from there without having to press the user button, provided a valid bootloader lives on the internal flash memory.

The exact process beyond loading the kernel is determined by the Linux distribution chosen. Depending on the revision of the BBB, this can be either Angström or Debian. Launching an application is specific to the Linux distribution and is beyond the scope of this book.