Firmware Overview - lalilulelulz/Chromium-OS-Coreboot GitHub Wiki

When you turn on an embedded device such as a Chromebook, the firmware is the first software that runs. It sets up the machine so that it can load the operating system and then transfers control to the OS. This general pattern applies to any architecture, but there are differences depending on the exact system architecture. For example, on ARM SoCs, it is common to have a boot ROM within the SoC that is capable of booting from various media and may set up basic clocks and peripherals.

On x86 systems, only the boot system is in SPI flash, and the firmware must deal with every aspect of setting up the machine. Typically, a first stage firmware such as Coreboot (not covered in this guide) is used on x86 to deal with these complexities. On x86, part of the firmware stays resident even after the OS runs, whereas on ARM and most other architectures, the firmware is no longer in memory once control transfers to the OS.