Patent ID: 7706097

Claim:
A magnetic disk drive comprising: a magnetic disk; a head which accesses the magnetic disk; a sensor section configured to detect an acceleration; a first judgment section which judges whether a drop is occurring based on an output of the sensor section; a processing section which executes a retraction of the head if the first judgment section judges that a drop is occurring; and a second judgment section which detects the occurrence of a shock based on the output of the sensor section; wherein, after the first judgment section judges that a drop is occurring, the processing section detects whether the drop judgment is incorrect according to whether the occurrence of a shock is detected by the second judgment section and changes the drop judgment condition of the first judgment section based on a history of detected incorrect drop judgments, wherein: the sensor section includes a gravity sensor which generates a detection signal by detecting a zero gravity state, and a shock sensor which detects a change in acceleration due to a landing shock; the first judgment section judges whether a drop is occurring based on the detection signal of the gravity sensor; and the second judgment section judges whether a shock is occurring based on the detection signal of the shock sensor.