Windows assigns a unique signature to each drive so that the Master Boot Record can keep of the drives. The MBR holds the code that loads the installed operating system.
These disk signatures can be viewed in Registry Editor. At Start type in rededit.exe, and Registry Editor will open. Then browse to HKEY_LOCAL_MACHINE\SYSTEM\MountedDevices.
The disk signature is only the first eight characters listed from the left in the 'Data' column, which is always comprised of digits 0-9 and letters A-F only. The characters which follow show the byte offset . This can be used to show the sector address of the drive - where on a partitioned optical disk the drive begins.