Disk device with improved error-correction capability

A disk device comprising:

• a disk drive including a head for reading data written to a disk and a processing circuit for processing the data;
• and
• a host computer connected to said disk drive through an interface;
• wherein the processing circuit of said disk drive includes a low-level error-correction code unit for performing error correction of the data written to a physical address corresponding to a single sector of the disk,
• the host computer includes a high level error correction code unit for performing error correction of the read data supplied through the interface and read from more than one sector of the disk,
• a high-reliability disk to which both a low-level error-correction code and a high-level error-correction code are written and a disk to which only the low-level error-correction code is written are loadable into said disk drive,
• when the high-reliability disk is loaded, the processing circuit of said disk drive performs low-level error correction, and then said host computer, to which the correction data is supplied, performs high level error correction, and
• when the latter disk is loaded, the processing circuit of said disk drive performs low-level error correction, and said host computer processes the corrected data.