sentences:  For example, in Windows certain registry keys use short filenames, which are sometimes not reproduced by file-based backup, some commercial software uses copy protection that will cause problems if a file is moved to a different disk sector, and file-based backups do not always reproduce metadata such as security attributes.Creating a bit-identical disk image is one way to ensure the system backup will be exactly as the original.Bit-identical images can be made in Linux with dd, available on nearly all live CDs.