It depends on what you call "Master password":
- BIOS user password (so you can start your computer at all, independent on your operating system)
- BIOS administrative password (so you can make changes to BIOS settings)
- your OS' "adminsitrative" password ("root" in Linux, "Administrator" (or first user) in Windows)
You can also have another password for unlocking the disk (either in BIOS or at OS level).
What you are trying to achieve?