ERROR CORRECTION METHOD AND ERROR CORRECTION CIRCUIT

1 . An error correction method comprising:

writing actual data having a first length together with additional data produced from source data to a magnetic disk having sectors having a read/write unit of a second length that is longer than the first length;

specifying one of the sectors to which actual data to be read have been written;

reading actual data and additional data from the specified sector;

verifying the read additional data with the source data; and

performing a first error correction on the read additional data based on a result of the verification.

2 . The error correction method as recited in claim 1 , wherein the verification of the read additional data comprises comparing the read additional data with the source data to find a difference between the read additional data and the source data, and

the first error correction of the read additional data comprises performing an error correction on the read additional data based on information on the difference between the read additional data and the source data.

3 . The error correction method as recited in claim 1 , further comprising:

performing a second error correction on entire data of the specified sector before the verification of the read additional data; and

determining whether or not to perform the verification of the read additional data based on a result of the second error correction of the entire data.

4 . The error correction method as recited in claim 1 , further comprising performing a third error correction on the read actual data based on a result of the first error correction of the read additional data.

5 . The error correction method as recited in claim 1 , wherein the writing operation of the actual data comprises:

dividing data including actual data and additional data to be written to one sector of the magnetic disk into a plurality of code words, and

performing a run length limited encode on at least a code word including the actual data to be written.

6 . The error correction method as recited in claim 5 , wherein the writing operation of the actual data further comprises:

preparing a plurality of sets of additional data to be written to the sector of the magnetic disk, and

adding one or more surplus bits to the actual data to be written and to each set of additional data to be written so that a length of data including the actual data and the surplus bits and a length of data including each set of additional data and the surplus bits are equal to 1/s of the code word where s is an integer.

7 . The error correction method as recited in claim 1 , wherein the writing operation of the actual data comprises:

dividing data including actual data and additional data to be written to one sector of the magnetic disk into a plurality of code words, and

performing a run length limited encode on only a code word including the actual data to be written,

wherein the source data comprises data produced within a range of the run length limited encode.

8 . The error correction method as recited in claim 1 , wherein the writing operation of the actual data comprises:

dividing data including actual data and additional data to be written to one sector of the magnetic disk into a plurality of code words,

generating an error detecting code from the actual data and the additional data, and

performing a run length limited encode on data other than the error detecting code.

9 . The error correction method as recited in claim 1 , wherein the source data comprises predetermined data.

10 . The error correction method as recited in claim 9 , wherein the additional data comprises a plurality of sets of dummy data produced from the predetermined data.

11 . The error correction method as recited in claim 1 , wherein the source data comprises the actual data.

12 . The error correction method as recited in claim 11 , wherein the additional data comprises a plurality of sets of duplicate data of the actual data.

13 . The error correction method as recited in claim 12 , wherein the verification of the read additional data comprises:

comparing the plurality of sets of duplicate data as the read additional data with each other to find a difference between the plurality of sets of duplicate data,

aggregating data elements in which the difference is found in the plurality of sets of duplicate data, and

determining which set of duplicate data includes an error based on a result of the aggregation.

14 . An error correction circuit comprising:

a writing unit operable to write actual data having a first length together with additional data produced from source data to a magnetic disk having sectors having a read/write unit of a second length that is longer than the first length;

a reading unit operable to specify one of the sectors to which actual data to be read have been written and to read actual data and additional data from the specified sector;

a verification unit operable to verify the additional data read by the reading unit with the source data; and

a correction unit operable to perform a first error correction on the additional data read by the reading unit based on a result obtained by the verification unit.

15 . A magnetic disk device comprising:

a magnetic disk;

a writing unit operable to write actual data having a first length together with additional data produced from source data to the magnetic disk, the magnetic disk having sectors having a read/write unit of a second length that is longer than the first length;

a reading unit operable to specify one of the sectors to which actual data to be read have been written and to read actual data and additional data from the specified sector;

a verification unit operable to verify the additional data read by the reading unit with the source data; and

a correction unit operable to perform a first error correction on the additional data read by the reading unit based on a result obtained by the verification unit.