Read boot sector or superblock
This dialog allows you to specify the location of the boot sector (from here on this means boot sector or superblock) of a volume.
Read from the current drive
Read the boot sector from the drive being scanned. It can be the primary or a backup boot sector of the volume. It can also be a temporary working copy created by the operating system. The disk sector number of the boot sector is only used to locate it. It is not used to compute the starting sector of the volume.
Read from a file
Use this option if the boot sector has been earlier saved to a file.
Generally this dialog is reserved for expert-level users with in-depth knowledge of file system on-disk formats.