Removable devices would be 1, cdrom 2, and 3 is hard drive. Removable is just
generic term for any USB drive, SD card, or Mini Flash. No harm is going to come
of changing the boot sequence. Unless it has Create Giant Vortex option and if
you have that option. For the love of humanity please do not select that. Unless
you been trained by Doctor Who or some none Red Shirt Space Federation officer.
Never a Red Shirt, because the life span for one is short lived. Basically a Red
Shirt is to the equivalent of an American Red Neck. When you hear "Hey ya'll
watch me do this"! You know some one is going to die.