1. Field of the Invention
The present invention relates to the field of the read error processing in magnetic disk drives. More specifically, the invention relates to a method of preventing read errors resulting from the thermal asperity (TA) of the servo area of the disk.
2. Background Information
A magnetic disk drive is a drive which writes data to the disk surface or reads data from the disk surface by a change of magnetization. A converter is positioned over a desired position on the track on which data has been recorded, and data is read out of the track of the disk rotating at high speed, or data is written to the track. The magnetic head of the magnetic disk drive is slightly spaced from the disk surface and positioned over a predetermined track. Magneto-resistive (MR) head has been adopted as one of the (magnetic field) conversion heads. The output resistance of the MR head changes as the magnetic field changes. This resistance change with a predetermined current to pass through the MR element converts MR resistance change to voltage signal, as reading out data.
However, the method of reading out this resistance change has a thermal asperity problem as one of its operational problems. The thermal asperity can be defined as follows. The large asperity of the disk surface touches a magnetic head and crashes, and temperature change causes resistance change to occur in the MR element. Because of this resistance change, an abnormal signal will occur.
The phenomenon of a thermal asperity often causes a strip temperature to rise to more than 100 degrees locally. The cause of this temperature rise is a mechanical crash between the head portion, including the MR stripe, and the asperity of the disk surface. Since the (normal) resistance change of the magnetic head by the magnetization change in the medium (disk), which is caused by normal reading, is less than 1% of the MR stripe resistance, the signal change resulting from the temperature rise, which is caused by the thermal asperity, largely exceeds the resistance change caused by a normal read signal, so normal data reading is hindered.
In conventional methods which cope with the thermal asperity with respect to data that is read out, when a sharp signal change, which would be determined to be a thermal asperity, is read out, an appropriate alternation is added to that read signal so that it can be processed as data, or that read signal is corrected with an error correction code. However, these conventional methods have the disadvantage that external additional hardware is required, or in the case of a large burst error which should be with an error correction code, correction becomes impossible and finally it should be processed as an unreadable hard error. Thus, the conventional methods cannot solve the thermal asperity problem sufficiently.