The whole purpose of dual-booting is to choose which OS you want to boot into. Traditionally, this is done in a clunky way, ...
In the era of floppy disks and early operating systems like CP/M and MS-DOS, A: and B: were reserved for floppy disk drives, ...
Booting from a USB stick is very helpful for many purposes. However, many factors have to be right for the boot to work ...