disk_error/21_READ_ERROR                               disk_error/21_READ_ERROR
 
 NUMBER
     21

 MESSAGE
     READ ERROR

 DESCRIPTION
     No sync character.
 
     The disk controller is unable to detect a sync mark on the desired 
     track. Caused by misalignment of the read/write head, no disk is 
     present, or unformatted or improperly seated disk. Can also indicate a 
     hardware failure.