Patent ID: 7636212

Claim:
A magnetic disk drive comprising: a magnetic disk for storing data; a magnetic head including a magnetoresistive effect element, said magnetic head at least reading data on the magnetic disk; a temperature sensor configured to detect the environmental temperature of the magnetic head; and a control unit configured to measure an error rate from a read signal of the magnetic head, and to receive an upper limit of the sense current; wherein said control unit detects a change in environmental temperature from an output of the temperature sensor, and determines a sense current of the magnetoresistive effect element that the best error rate can be achieved while remaining below the upper limit of the sense current, and then sets the sense current below the upper limit; wherein the upper limit of the sense current is a value that is determined from the viewpoint of the reliability of the magnetoresistive effect element wherein: when an increase in environmental temperature is detected, said control unit determines said sense current by repeatedly performing: measuring an error rate at the environmental temperature in question, said error rate being defined as an initial value; increasing the sense current by a specified value; making a check as to whether or not said increased sense current has exceeded the upper limit that is determined from the viewpoint of the reliability of the magnetoresistive effect element; if it is judged that the increased sense current has not exceeded the upper limit, setting the increased sense current as a new sense current; measuring an error rate for the new sense current; comparing the error rate for the new sense current with the error rate defined as the initial value; and if the error rate for the new sense current is smaller than the error rate defined as the initial value, setting the new sense current as an optimum value, and defining the error rate for the new current as the initial value.