Positions in which errors have occurred are found more accurately and erasure
correction is performed more effectively than in cases where TA flags or error
flags issued by the R/W channel are utilized as information indicating the positions
in which errors have occurred, [this being accomplished] by reading the same sector
on the magnetic disk a plurality of times, storing the plurality of NRZ data thus
obtained, comparing these NRZ data in byte units, judging that an error has occurred
in byte positions where the NRZ data reproduced in each read operation differs,
and utilizing these positions as erasure pointers for erasure correction.
