From where am I booting

[BigLinux]

What are the commands that could be ran from the command line, that could be used to figure out from which device I am currently booting from?

For example, I have the exact same Linux on a CD and HDD. Once I am booted up into a system. It all looks the exact same. How can i tell if I am actually running from the CD?

I need this information for a prank

[Showstopper]

On your system settings you have have Boot from a disc before Boot from HDD?

[BigLinux]

If you mean the BIOS sequence yes... but I can change that if needed

[Showstopper]

If you have it booting from a disc then its probably booting from the disc.