NTBackup
From Just Solve the File Format Problem
Windows NTBackup is backup/archiving software utility included in Windows NT 3.51, Windows NT 4.0, Windows 2000, Windows XP Pro, and Windows Server 2003.[1][2]
File Information
Windows NTBackup would backup a file or a folder into a BKF file. It has been replaced by the wbadmin command.[3]
Format Information
BKF backup files begin with the ascii TAPE
or hex values 54415045