Both SU and BSEGY are similar to the exchange format, SEGY in that they use a 240 byte trace header followed by a data block. This way, the headers are locked to the data. Neither SU or BSEGY uses a reel header, since that goes back to the days of 9 inch tape.
BSU also supports dumping data to text and comma separated variable formats for those who just want to get the binary format out into something they can use in software like Matlab or Spread Sheets.