According to one embodiment, a magnetic disk device reads servo information from a recording surface of a magnetic disk using a head, detects a position of the head based on the servo information, and estimates a vibration frequency of a disturbance applied to the head and filtering the estimated vibration frequency from a drive signal of the head. In the filtering, a position error is calculated using a target position of the head given when driving the head and the detected position of the head, a plurality of the vibration frequencies is estimated by executing the vibration frequency estimation based on the position error in a plurality of stages in series, and estimation results of the vibration frequencies are filtered in parallel from the drive signal of the head.

According to an embodiment, on a first track of a magnetic disk, a plurality of first sectors in each of which a data segment is stored, and a second sector in which a parity for first error correction is stored are arranged in this order from a first position. A controller executes a first operation of sequentially reading a first data segment from each of the plurality of first sectors, and storing a group of the read first data segments in a buffer memory. The controller obtains a first parity from the group of the read first data segments. The controller starts a second operation of writing each first data segment stored in the buffer memory, to a first sector that is a read source among the plurality of first sectors, and writing the first parity to the second sector, before the magnetic head reaches the first position.

A method of operating a storage device includes reading data from a storage medium using a detector, processing signals from the detector through a plurality of processing circuits, each respective processing circuit in the plurality of processing circuits being optimized for a different state of a channel condition and providing a respective output metric, selecting a processing circuit from the plurality of processing circuits by comparing the respective output metrics from each processing circuit in a predetermined manner, and designating as output of the detector output of the processing circuit that is selected. The output metrics may be branch metrics or path metrics, and the channel condition may be fly-height or phase shift. The storage device includes a storage medium, and a read channel including a detector, and processing circuits that process signals from the detector. Each respective processing circuit is optimized for a different state of a channel condition.

According to one embodiment, a magnetic disk apparatus includes a magnetic disk, a magnetic head, and a controller. The magnetic disk is provided with a track including a plurality of first sectors. The controller accesses the magnetic disk by using the magnetic head. The plurality of first sectors includes a plurality of second sectors where data segments are written and a third sector where parity and first information indicating effectiveness or ineffectiveness of protection by the parity are written.

A pad/trace line layout for a PMR writer structure having two or more writers on a slider, and a process for selecting the best of the multiple writers is disclosed. Each writer is individually probed with a spin stand test device to generate performance results including bit error rate (BER), and area density capability (ADC). After the best writer is determined, the slider is integrated in a HGA. Only the best writer is connected through trace lines to a preamp to enable functionality. At least one trace line has a plurality of arms that enable flexibility in connecting the best writer to the preamp while other arms are not connected. In some embodiments, all writers share a common W pad that is connected to the preamp through one of two trace lines while the other trace line has one of the plurality of arms connected to the best writer.

A data storage device is disclosed comprising a first voice coil motor (VCM) comprising a first voice coil configured to actuate a first head over a first disk, and a second VCM comprising a second voice coil configured to actuate a second head over a second disk. The data storage device further comprises a spindle motor configured to rotate the first and second disk, wherein during a power failure the first and second disks rotating causes the spindle motor to generate a back electromotive force (BEMF) voltage. During the power failure, the BEMF voltage is applied to the first VCM and to the second VCM during a first interval. The BEMF voltage is monitored, and when the BEMF voltage falls below a first threshold, the BEMF voltage is disconnected from the first VCM and the second VCM during a second interval.