Select Backup Device
Use the Select Backup Device dialog box to select a logical backup device for the restore operation.
A logical backup device is a user-defined logical device that corresponds to a physical device, either a tape drive or a disk drive, that is provided by the operating system.
If a backup uses multiple backup devices, they all must correspond to a single type of device.
To use SQL Server Management Studio to view the contents of a backup device
If you do not see a logical backup device that contains the backup you are seeking on the list, the backup might have been written directly to one or more files or tape drives. If this is the case, cancel the Select Backup Device dialog box; and in the Specify Backup dialog box, select File or Tape in the Backup media list box. For more information, see Specify Backup.