According to one embodiment, a magnetic disk device includes a disk, a head that writes data to the disk and reads data from the disk, and a controller. The controller is configured to read first data written on the disk, measure a first read error rate of the first data, determine a difference in the first read error rate from a previously determined read error rate of the first data, determine a current read error rate for second data written on the disk based on the difference in the first read error rate from the previously determined read error rate, and determine whether a refresh process is performed on the second data based on the current error rate.

An optical disc device includes a first error correction coding circuit that codes the recording data according to a first error correction coding format, a second error correction coding circuit that codes the recording data according to a second error correction coding format, and a recorder that converts the recording data into a recording signal and records it on an optical disc. The second error correction coding format is different in an arrangement of the recording data from the first error correction coding format. The second error correction coding format is configured to generate a second parity code with a higher degree of redundancy. The recorder records the recording data coded by the first error correction coding circuit and only the second parity code in the recording data coded by the second error correction coding circuit.

A multi-gear ECC decoder includes a high power decoder and a low power decoder. In order to significantly reduce the decoding time for high-BER codewords using a slow high power decoder, rather than decoding codewords in either slow high power or fast low power, a controller switches between slow high power decoding and fast low power decoding during the decoding process. The controller first will determine, based on a predetermined factor, whether to start decoding in slow high power or fast low power. Once a decoding power is determined, then the decoding will begin. During the decoding process the decoding transitions from a first power lever decoder to a second power level decoder. The decoding will continue in the second decoding power level after the transition, until the decoding is completed or if another switch needs to occur for insufficient decoding.

A multi-gear ECC decoder includes a high power decoder and a low power decoder. In order to significantly reduce the decoding time for high-BER codewords using a slow high power decoder, rather than decoding codewords in either slow high power or fast low power, a controller switches between slow high power decoding and fast low power decoding during the decoding process. The controller first will determine, based on a predetermined factor, whether to start decoding in slow high power or fast low power. Once a decoding power is determined, then the decoding will begin. During the decoding process the decoding transitions from a first power lever decoder to a second power level decoder. The decoding will continue in the second decoding power level after the transition, until the decoding is completed or if another switch needs to occur for insufficient decoding.