As I study GRUB, & as my explorations of how I'd implement internal storage has my considering the boot process for my hypothetical...
I'm thinking: What does a boot loader do?
Primarily it renders a menu asking which OS you want to boot, without depending on that OS already running. The tricky part is the latter!
Secondarily it provides tools to help you recover in case your operating system isn't booting.
Earlier stages of the boot chain (from your hardware vendor) provides drivers.
