Magnetic disk device

A magnetic disk device comprising:

• a disk;
• a head;
• a head position demodulation unit which demodulates a position of the head (head position) by performing switching between normal servo demodulation for processing servo information written to a servo sector of the disk and short servo demodulation for processing servo information by a short servo system;
• and
• a controller which controls the position of the head, wherein
• the controller comprises:
• a head position prediction unit which predicts a head position;
• and
• a write inhibition determination unit which determines that data write operation to the disk by the head is inhibited based on the predicted head position (head prediction position), and
• the head position prediction unit performs position prediction by using a latest head position obtained by demodulation by the head position demodulation unit and a head position obtained by past demodulation by normal servo demodulation,
• the controller further comprising:
• a first position prediction unit which calculates a prediction position by a first calculation formula when the latest head position is a head position (normal head position) obtained by the normal servo demodulation;
• and
• a second position prediction unit which calculates the prediction position by a second calculation formula which is different from the first calculation formula when the latest head position is a head position (short head position) obtained by the short servo demodulation.