Exception is the partition(volume) boot record.
    May be accessed before OS is up..

    Volume information.

    OS Bootstrap program. 
 
  NTFS keeps 2 copies of 1st 16 entries of volume boot records.
    1st located at sector 0 of volume.

    2nd at middle of volume (NT 3.51) 

    or end of volume (NT 4.0 ^, Win 2000,XP)