A magnetic disk device of an embodiment includes: a head structure including at least one reproducing head and main magnetic pole gap installation portion behind a flying slider and including at least two thermal actuators; and a control unit that can independently control the thermal actuators and that sets spacing of the reproducing head and the main magnetic pole gap installation portion with respect to a recording medium by setting a rotational speed at the time of contact, which rotational speed is a rotational speed of the recording medium, to be lower than a normal rotational speed when the reproducing head and the main magnetic pole gap installation portion are brought into contact with the recording medium.

An apparatus comprises a laser diode configured to generate light during a write operation. A slider comprises a near-field transducer (NFT) and an optical waveguide. The slider is configured for heat-assisted magnetic recording and to communicate the light to the NFT via the waveguide. A writer heater of the slider is configured to receive power during the write operation. A thermal sensor is situated at or near an air bearing surface of the slider. The thermal sensor is configured to produce a sensor signal in response to sensing back-heating from the medium while the NFT generates heat during a write operation. Circuitry, coupled to the thermal sensor, is configured to compare the sensor signal to a threshold and generate an output signal indicative of degradation of NFT performance in response to the sensor signal exceeding the threshold.

According to one embodiment, a magnetic disk drive selects in command evaluation in reordering processing, a command accessible in a shortest time. The device determines whether media bumps which influence a dynamic flying height (DFH) control exist in a seek section between completion of a previous command and start of a selected command or not, calculates a latency necessary for avoidance of the media bumps if it is determined by the determination that the media bumps which influence the DFH control exist, and selects the command accessible in the shortest time including the time obtained by summing the latency calculated by the calculation as the command to be next processed.

A hard disc drive includes a slider including a first reader and a second reader. The hard disc drive also includes a magnetic recording medium and a controller. The controller is configured to determine a distance between the slider and the magnetic recording medium based at least in part on amplitudes of read signals from both the first reader and the second reader.

A disc drive includes a data storage surface having a system data zone and a user data zone, and a head that communicates with the data storage surface. The disc drive also includes a control circuit communicatively coupled to the head. The control circuit is configured to, during power up initialization of the disc drive, apply a fly height control value to direct the head to fly at a first target fly height for reading system data from the system data zone. The first target fly height is substantially higher than a second target fly height for reading user data from the user data zone. The control circuit determines whether an actual fly height of the head is substantially equal to the first target fly height. The control circuit performs fly height correction when the actual fly height is not substantially equal to the first target fly height.

Apparatus and method for reducing the effects of thermal asperities on a rotatable data recording surface. A data transducer writes user data to a first set of tracks at a first fly height above the recording surface. A compensation circuit detects a thermal asperity (TA) on the recording surface, and establishes a guard band as a second set of tracks that are co-radial with the TA. The second set of tracks are deallocated and removed from service. The compensation circuit further defines a reserve band as a third set of tracks immediately adjacent the guard band, and selects an increased, second fly height that allows the data transducer to write data to the reserve band without contacting the TA. The second set of tracks may have a greater track pitch than the first set of tracks to compensate for the greater fly height.

An apparatus comprises a laser diode configured to generate light during a write operation. A slider comprises a near-field transducer (NFT) and an optical waveguide. The slider is configured for heat-assisted magnetic recording and to communicate the light to the NFT via the waveguide. A writer heater of the slider is configured to receive power during the write operation. A thermal sensor is situated at or near an air bearing surface of the slider. The thermal sensor is configured to produce a sensor signal in response to sensing back-heating from the medium while the NFT generates heat during a write operation. Circuitry, coupled to the thermal sensor, is configured to compare the sensor signal to a threshold and generate an output signal indicative of degradation of NFT performance in response to the sensor signal exceeding the threshold.

According to one embodiment, a magnetic disk drive selects in command evaluation in reordering processing, a command accessible in a shortest time. The device determines whether media bumps which influence a dynamic flying height (DFH) control exist in a seek section between completion of a previous command and start of a selected command or not, calculates a latency necessary for avoidance of the media bumps if it is determined by the determination that the media bumps which influence the DFH control exist, and selects the command accessible in the shortest time including the time obtained by summing the latency calculated by the calculation as the command to be next processed.

Gain values used by a variable gain amplifier (VGA) to read servo marks of a heat-assisted recording medium are measured. Sector-specific, repeatable gain values that indicate an expected VGA gain at a desired clearance are determined based on the measured gain values. The sector-specific, repeatable gain values are used as input to a closed-loop clearance controller together with measured values of servo VGA gain while writing data to the recording medium.

According to an embodiment, a circuit includes a biasing and a low-frequency recovery circuit. The biasing circuit includes a voltage digital to analog converter (V-DAC), a differential difference amplifier coupled to the V-DAC, a common-mode feedback (CMFB) amplifier coupled to the differential difference amplifier, and a first pair of transistors arranged as a high-impedance structure and coupled to the differential difference amplifier and the CMFB amplifier. The low-frequency recovery circuit includes a current digital to analog converter (C-DAC), a second pair of transistors arranged as a high-impedance structure and coupled to the first pair of transistors, a pair of resistors having a resistance value equal to half a resistance of the resistive sensor, the pair of resistors arranged between the second pair of transistors and coupled to the C-DAC, and a gain circuit coupled to shared nodes between the second pair of transistors and the pair of resistors.