I don't think one can refer to a microcontroller as a device that boots, unless one has written a bootstrap program. I think one should state that a microcontroller starts (or executes) a program... It does not actually boot like a PC does...

But this is probably nitpicking... and does not help you any further... except when it makes someone aware that a microcontroller does not do anything unless it's been programmed by the user...

Come to think of it: some microcontroller "species" do have an initial "boot" procedure, allowing them to be programmed by means of a serial i/f... but then they still don't do anything besides waiting to be programmed by a user...

regards
Patrick