Abstract: According to one embodiment, a control device includes a writer, a setting module, a reader, and an Iw sensitivity acquiring module. The writer writes a signal by the magnetic head. The setting module sets an electric parameter to the magnetic head. The reader reads the signal by the magnetic head. The Iw sensitivity acquiring module acquires Iw sensitivity of the magnetic head. The Iw sensitivity acquiring module includes a first acquiring module, a second acquiring module, and an Iw sensitivity calculator. The first acquiring module acquires a predetermined output value related to control of a signal having a predetermined frequency. The second acquiring module acquires a predetermined output value related to control of the signal having the predetermined frequency. The Iw sensitivity calculator calculates the Iw sensitivity of the magnetic head based on the predetermined output values acquired by the first and second acquiring modules.

Abstract: A final area retrieving apparatus, an information reproducing apparatus, a final area retrieving method, and a final area retrieving program are provided, which are capable of decreasing a period of time necessary for acquiring information necessary for reproduction of optical disc. When a final area of optical disc D is retrieved, a system control unit 6 stores a start address of the area, and the like in a flash memory 5. When the optical disc D is inserted again, and a final area is newly retrieved, it is determined whether a final area retrieved at the last time exists on the optical disc D, based on a starting address of final area stored in the flash memory 5. In a case where it is determined that a final area retrieved at the last time exists on the optical disc D, the acquisition of start address of next area, and the like is started from a final area retrieved at the last time, and a final area is retrieved.

Abstract: A signal quality evaluating method necessary for a signal quality evaluation index and a margin design is provided for an apparatus utilizing hologram recording techniques. An evaluation index is used being obtained by dividing root sum square of standard deviations of luminance value distribution of on- and off-pixels obtained from reproduced signals, by a difference between average values.

Abstract: In an optical disc having N (N is an integer larger than or equal to 3) information recording layers of rewritable or recordable type, each of the information recording layers includes an test area to adjust conditions for recording and reproduction and the test areas are arranged so that the radial positions thereof overlap those of other layers. Recording test is performed only to an area smaller than or equal to 1/N of the test area of each layer and any other area is always unrecorded (write inhibited).

Abstract: In a recording medium, an extension address is obtained without changing the number of bits of the address embedded in the wobble. The wobble address is partially or wholly encoded to embed the address information. At the time of reproducing the address information, the original address information is obtained by restoring the embedded information by the decoding process.

Abstract: According to the present invention, whether recoding pits are larger or smaller than diffraction limit is determined. Then, a signal process suitable for processing of the recording pits larger than the diffraction limit and a signal process suitable for processing of the recording pits smaller than diffraction limit are divided to divisionally perform equalizer processing. The respective signals subjected to the divisional processing are synthesized to obtain a processed output signal. A reproduction signal with reduced impact of intersymbol interference is thus obtained.

Abstract: An optical storage system includes an optical pick-up head for receiving and transforming an optical signal into an electric signal; a pre-amplifier for receiving the electric signal and outputting a RF signal and a position error signal; a data and timing recovery unit for receiving the RF signal and generating a modulated signal and a clock signal; an error correction unit for generating a data signal according to the modulation signal and the clock signal; a defect signal generator for receiving the RF signal and generating a defect signal according to the RF signal, wherein the defect signal is enabled when the RF signal has a defect; and an error correction controller for receiving the defect signal and generating an error correction control signal according to the defect signal, wherein the error correction unit further receives the error correction control signal and adjusts the decoding strategy of the error correction unit according to the error correction control signal.

Abstract: In an optical information recording device and optical information recording method for angularly multiplexing and recording data on pages on the same recording region on a hologram disk, data on each page is sequentially generated by sequentially dividing input data in predetermined units, the pages to be recorded on the same recording region are divided into page groups so that pages to be recorded adjacently by the angular multiplexing may not belong to the same group, each page group is individually subjected to inter-page coding processing for computing an error-correcting code and adding the computed error-correcting code, and data on the pages subjected to the inter-page coding processing is angularly multiplexed and recorded on the hologram disk.

Abstract: An optical head 12 reproduces information recorded on an optical disc 11, a BCA detector 21 and a medium discriminating circuit 22 acquire waveform distortion information for specifying a waveform distortion of a reproduction signal reproduced by the optical head 12, and a variable waveform equalizer 16 changes a parameter used in a distortion reduction processing for reducing the waveform distortion of the reproduction signal based on the waveform distortion information.

Abstract: A light beam is scanned on a track of a recording medium, the track having a first track region and a second track region, each track region having a physical property that has recurring deviations. A wobble signal is derived from the light beam, the wobble signal having information associated with the recurring deviations. Whether the light beam is at the first track region or the second track region is determined based on a frequency, a period, or a pulse width of the wobble signal.

Abstract: An optical disc reader comprising a controller that controls a read operation to read data recorded on an optical disc and a counter that counts the number of zero crossings in a tracking error signal. Between the completion of focusing operation and the start of tracking operation, the controller determines whether or not the light beam is properly focused on a data recording layer in the optical disc based on the number of zero crossings in the tracking error signal counted by the counter. If it is determined that the light beam is not properly focused, the controller causes the focusing operation to be performed again. Otherwise, if it is determined that the light beam is properly focused on the data recording layer, the controller causes the tracking operation to be performed and then starts the read operation.

Abstract: According to one embodiment, a medium recording device includes a reading/writing module configured to read/write data from/to a recording medium, a buffer memory configured to temporarily store the read data and data from a host, and a controlling circuit configured to, in response to a read command, read data from the buffer memory or the recording medium to transfer the data to the host, and in response to a write command, to store data from the host in the buffer memory, to write the data onto the recording medium, and to execute a write retry when writing fails. The controller circuit recognizes a read command issued by the host at a fixed interval for replaying continuous data, and determines whether write in response to a write command received during the replaying is likely to fail, and when the write is likely to fail, permits a reception of the read command issued at the fixed interval.

Abstract: A disk drive transporter, for transporting a disk drive and for mounting a disk drive within a test slot, includes a frame configured to receive and support a disk drive. The frame includes sidewalls configured to receive a disk drive therebetween and sized to be inserted into a test slot along with a disk drive. The frame also includes a clamping mechanism operatively associated with at least one of the sidewalls. The clamping mechanism includes a first engagement element and a first actuator operable to initiate movements of the first engagement element. The first actuator is operable to move the first engagement element into engagement with a test slot after a disk drive being supported by the frame is arranged in a test position in a test slot.

Abstract: A highly efficient and reliable reproduced signal evaluation method and an optical disc drive using that method in which assuming that the number of 2T's appearing successively in a predetermined evaluation bitstream is i, the evaluation bitstream is divided into a main bitstream (5+2i) long and sub bitstreams at the ends of the main bitstream. The check process to determine whether a predetermined evaluation bitstream is included in the binarized bitstreams is replaced with a main bitstream agreement check. This can prevent an increase in the circuit size. At the same time, by separately summing up for each main bitstream the calculated results of Euclidean distance between the reproduced signal and the target signal corresponding to the evaluation bitstream, the size of an evaluation summing circuit can be reduced.

Abstract: According to one embodiment, a magnetic disk apparatus comprises a magnetic disk configured to store encrypted data, a magnetic head configured to read data from and to write data to the magnetic disk, and a recording and reproducing circuit connected to the magnetic head, wherein the recording and reproducing circuit configured to read data from an area of the magnetic disk, to decrypt read data, to re-encrypt decrypted data with changing a cipher key, and to rewrite re-encrypted data in the area of the magnetic disk.

Abstract: A method of detection is described to be used in file system-based player devices to determine the type of compact disk that has been inserted into a player. The method automatically distinguishes between the DTS-CD format and standard audio CDs. The method allows the operating system or CPU software to take appropriate action to decode and playback the audio stream once the a decision between standard audio CD or DTS-CD is made.

Abstract: In a recording/reproducing system that performs PRML decoding, a suitable evaluation value for setting a recording condition can be obtained with a simple structure. It is assumed that a value corresponding to a difference between a difference metric between a maximum likelihood path for an equalized signal that is fed to maximum likelihood decoding processing and a path in a bit-advanced shift direction and a difference metric between the maximum likelihood path for the equalized signal and a path in a bit-delayed shift direction is a signal quality evaluation value dSAM. Further, the signal quality evaluation value dSAM is calculated using an equalization error value ek which is an error between an equalized signal value fed to the maximum likelihood decoding processing and an ideal equalized signal value determined from a decoded signal obtained as a result of the maximum likelihood decoding processing.

Abstract: According to one embodiment, a disk drive includes a medium scanner and a threshold manager. The medium scanner measures the write count of each head with respect to a disk. The medium scanner executes a read verify process by which data is read out from the disk, during idle state, when the write count is equal to or larger than a predetermined threshold value. The medium scanner rewrites the recovered data to the disk, if a read error occurs and the error is recoverable. The threshold manager initially sets the write count threshold value of each head in accordance with the head performance, and dynamically changes the write count threshold value in accordance with the error rate when the device is in operation.

Abstract: The present invention is aimed at providing an optical disc device and a recording condition setting method which can automatically determine an optical recording condition to an optical disc, and the optical disc device comprises an optical pickup which records data on a disc; a data encoder which modulates data to be recorded; a recording timing setting means which sets a timing of recording the data on the disc; a phase error detection means which measures an error amount of a mark recorded on the disc from a position where the mark should be properly located; an error convergence means which calculates error information indicating an optimum position of the mark; a recording timing calculation means which calculates a correction value of the recording timing to be set on the recording timing setting means, based on the error information; and a control means which feedbacks an output of the recording timing calculation means to the recording timing setting means, thereby to optimize the recording timing.

Abstract: An information recording apparatus mutually communicates with a number-of-copying-times management server via a communication network, the server performing management by correlating medium identification information that enables unique identification of an information recording medium, with information related to number of allowable copying times of digital contents recorded on the information recording medium. The apparatus acquires the medium identification information of the inserted information recording medium, and acquires information related to the number of allowable copying times correlated with the acquired medium identification information, from the number-of-copying-times management server, for recordation in a storage unit.

Abstract: Spherical aberration correction is provided for CD writing in a double (CD+DVD), triple (CD+DVD+BD) or quadruple (CD+DVD+BD+HD-DVD) writer, which use the same light path for CD and DVD. In an optical drive that uses numerous laser wavelengths combined into one light path each wavelength having a different numerical apertures a correction for spherical aberration is made to correct for effective numerical apertures of the light path that becomes shifted up from the original value to higher values. The correction in spherical aberration removes that effect of the higher effective NA and defects, particularly in writing, are corrected.

Abstract: A hard disk drive with a patterned disk that has a discrete track. The disk drive includes a controller that controls a head and a voice coil motor to optimize a writing of information onto the discrete track. Writing optimization can occur by initially writing a track of information and recording the write position. The written track is then located by reading the information with a read element of a drive head and analyzing a quality of the read signal, such as signal amplitude or error rate. The read position is then recorded. The information is erased and the head is moved. The process of writing, finding the written track location, storing the write and read positions and again moving the head is repeated. The write and read positions that provide the best quality signal is saved and subsequently used to write and read data on the discrete track.

Abstract: A method of determining a recording power used to record information to an optical disc, includes carrying out test recording which records predetermined data to a predetermined area of the optical disc to determine the recording power, and recording predetermined data with a power equal to or more than the determined recording power to an area adjacent to the predetermined area.

Abstract: A system for grading defective bit patterned magnetic media by disk sector in hard disk drives recovers a portion of any defective sectors at a lower areal density. The invention reduces the track pitch density for sectors containing amalgamated islands while leaving the remainder of the defect-free sectors in the zone optimized for linear bit density. This recovers a portion of the defective sector, approximately in proportion to the ratio of amalgamated islands over the original number of islands. A typical zone is first optimized for tracks per inch during formatting of the patterned media disk drive. The zone is then broken up into sectors that can each be optimized separately for linear bit density to ensure the maximum sustainable capacity for each sector.

Abstract: The invention relates to an optical recording apparatus on optical carrier or disk, the apparatus has means for sampling a power level of an irradiation beam, e.g. a laser beam, that is capable of recording data in a data region (101) in response to an predefined input signal (NRZ). The irradiation beam (5) has a substantially constant power level in a first period (MT1), where the first period (MT1) is longer than the period of time associated with the maximum code run length (MRL) of the encoding scheme. Forward photo sensing means (FS 41, 40) is adapted to sample the power level in at least a sub-period of time (ST1) of the first period (MT1). The invention relaxes the requirements of the forwarding photo sensing means (FS), as the first period (MT1) may be extended beyond the time that was previously available for monitoring the power level of the irradiation beam.

Abstract: A method of controlling a temperature of a subject test slot in a cluster of test slots includes evaluating a request for a temperature change for the subject test slot to determine if sufficient power is available to achieve the requested temperature change, and inhibiting the requested temperature change unless or until sufficient power is determined to be available to achieve the requested temperature change.

Abstract: According to one embodiment, a storage apparatus includes: a reader configured to read a sector recorded in a storage medium; a detector configured to detect a sync mark in the sector; a determiner configured to determine the position of the data region of the sector based on the sync mark detected by the detector; a data generator configured to generate data of the data region based on the data region, the position of the data region being determined by the determiner; a first judging module configured to judge whether the data generated by the data generator is normal; and a data compartment recorder configured to record a data compartment in the storage medium distinguishably from other data compartments, the recorded data compartment comprising a data region from which, among the data generated by the data generator, data judged as abnormal is generated.

Abstract: According to one embodiment, in a disk drive, a voice coil motor is controlled to cause a head to minutely vibrate in a radial direction on a track of a disk. When the voice coil motor vibrates the head in the radial direction of the disk, frictional force occurring between the disk and the head is calculated based on the driving force of the voice coil motor generated to vibrate and detected positional information, thereby measuring frictional characteristics.

Abstract: An optical disk drive for determining a disk characteristic of an optical disk comprising an information layer comprising a substantially circular track is described. The optical disk drive has an optical pickup unit arranged to generate a beam, direct the beam to the optical disk for forming an incident beam, sense a reflected beam produced by the optical disk with a sensor upon receiving the incident beam with the sensor, produce a sensor output signal from sensing the reflected beam; a disk receiving device arranged to receive the optical disk; a motor arranged to provide a transition of the disk receiving device from a first mode to a second mode in at least one transition phase; and a controller arranged to receive the sensor output signal during at least one part of the at least one transition phase and perform at least part of determining the disk characteristic from at least the sensor output signal received during the at least one part of the at least one transition phase.

Abstract: According to one embodiment, a test device for a storage device includes: a module configured to acquire from the storage device a value corresponding to a signal level read from a magnetic disk through a magnetic head of the storage device, at a first timing at which an initial power of 0 or greater is supplied to a heater in the head and at a second timing at which a power to the heater is returned to the initial power after the power to the heater has been increased from the initial power, a periphery of a head element in the head has been expanded by the heater, and the element has been protruded toward a magnetic disk side; and a determiner configured to determine whether plastic deformation has occurred in the periphery of the element based on a difference between the values obtained at the first and second timings.

Abstract: According to one embodiment, a method of writing servo information comprises: moving a head at a predetermined pitch in the radial direction of a storage disk to write servo information to each radial direction position in the circumferential direction of the storage disk; detecting a positional deviation value of the head while the servo information is being written to the radial direction position and determining whether the positional deviation value exceeds a predetermined value; and writing, when the positional deviation value exceeds the predetermined value, the position of defective servo information where the positional deviation value exceeds the predetermined value to a predetermined position in the radial direction of the storage disk.

Abstract: A method for testing a mold structure including magnetically transferring a magnetic signal according to a concavo-convex pattern for a servo area in a mold structure to a perpendicular magnetic recording medium; electrically reproducing ?50 tracks of the magnetic signal of servo data transferred onto the perpendicular magnetic recording medium using a magnetic head to obtain a reproduction signal; and calculating a pattern drawing accuracy radially from the reproduction signal to evaluate a performance of the mold structure including a disc-shaped base material; and the concavo-convex pattern for the servo area and a concavo-convex pattern for a data area formed on a base material surface following a desired design pattern. The concavo-convex patterns for the servo area are aligned in the radial direction of the base material, and the concavo-convex pattern for the data area are aligned in the circumferential direction between the concavo-convex patterns for the servo area.

Abstract: An information recording medium according to the present invention includes a track on which a data sequence including a plurality of recording marks and a plurality of spaces provided between the plurality of recording marks is recordable; and a recording condition recording area in which a recording condition for recording the data sequence on the track is recordable.

Abstract: The described implementations relate to DVD identification. One method accesses media content from a DVD and identifies a format of the media content. The method also determines a unique identification for the media content based upon the format.

Abstract: According to one embodiment, a method evaluates a head comprising a read element, a recording element, a coil, and a heater to change a projection amount of the elements by thermal expansion. The method includes: floating the head over the medium rotated; projecting including conducting electricity through the heater with an electric power, and projecting the elements toward the medium; first recording including stopping the conduction, and recording data in a sector on the medium after the stopping; second recording of recording data in another sector on the medium; reproducing the recorded data to obtain their reproducing characteristics; and obtaining including repeating the projecting, first and second recording, and reproducing, while changing the electric power in the projecting, obtaining the electric power for the heater at which the characteristics equal each other to compute the projection amount due to a current fed through the coil upon recording.

Abstract: A method models and calibrates the fly height of a slider above the disk for disk drives. The calibration scheme uses the Wallace spacing loss equation and laser doppler velocimetry to predict fly height and detect the actual fly height of the slider. The slider is vibrated at selected resonances, such as by capacitive coupling to the disk, and the fly height is gradually reduced. In one version, contact between the slider and disk may be detected using an arm electronics sensor. The amplitude of mean-to-peak, vibration detection is used as an indication of the actual fly height and to calibrate the modeled fly height.

Abstract: A method for controlling proximity of a read element of a perpendicular-magnetic-recording (PMR) head to a PMR disk. The method includes: a) writing recorded data with a write element of the PMR head to the PMR disk; b) providing a proximity-control setting to a proximity-control element; c) positioning the read element of the PMR head with the proximity-control element as determined by the proximity-control setting in communication with the PMR disk for reading recorded data back from the PMR disk; d) measuring a resolution of a read-back signal of recorded data on the PMR disk associated with the proximity-control setting; e) determining if the resolution measured for the read-back signal of recorded data on the PMR disk satisfies a criterion for the resolution of the read-back signal of recorded data; and, f) changing the proximity-control setting, and repeating b), c), d) and e), unless the resolution satisfies the criterion.

Abstract: A system in one embodiment includes a disk; a reservoir having a selectively openable cover; a lubricant in the reservoir; and a sensor for detecting an event or condition that triggers opening of the cover. A method in another embodiment includes determining that a trigger event or a trigger condition is occurring or has occurred in a hard disk drive; opening a cover of a lubricant reservoir for allowing egress of lubricant therefrom upon determining that the trigger event or the trigger condition has occurred; and closing the cover of the lubricant reservoir after a period of time. Additional systems and methods are also presented.

Abstract: A method for utilizing idle times during read/write operations for a personal video recorder (PVR) is described. Idle times during read/write operations are predicted and then such idle times are used to perform hard disk maintenance functions.

Abstract: An optical disk drive, and a method of determining a write strategy thereof. In the method of determining a write strategy of an optical disk drive where a mark and a space are formed on an optical disk by a laser beam to display write information and information is written or reproduced, write quality is evaluated by combining at least two of power- and pulse-based parameters defining a writing multi pulse, and the at least two parameters are changed on a 2-dimensional matrix. The power- and pulse-based parameters indicating specific write quality are determined as strategy parameters, based on evaluated results of the write quality.

Abstract: A method for optimizing design parameters of a magnetic write head. The method involves compiling a table of data points for a plurality of design parameters. An experimentally derived optimal design point is determined a first set of tests are performed at this experimentally determined design point. A three dimensional response surface is generated based on the testing. Then, a projected optimal design point is determined from the three dimensional response surface. Another test is performed using this projected optimal design point, and a convergence is determined by comparing the results of the first and second tests. If the convergence is within a predetermined value, then the process is complete. If the convergence is not within the predetermined value, then the process is repeated using the most recent projected optimal design point.

Abstract: In one embodiment, a magnetic disk drive includes a magnetic disk, a head slider for flying above the spinning magnetic disk, a pattern analyzer for analyzing a data pattern of data to be recorded on the magnetic disk to determine a recording current reversal timing and a recording assistance area in accordance with the analysis so that the rear end of the determined recording assistance area is shifted forward if the determined recording current reversal timing is earlier than a criterion, or the rear end of the determined recording assistance area is shifted backward if the determined recording current reversal timing is later than the criterion, a recording assistance element on the slider for forming the determined recording assistance area on the magnetic disk, and a recording element for recording the data on the magnetic disk using the recording current in accordance with the determined recording current reversal timing.

Abstract: According to one embodiment, a vibration correspondence information storage module stores, each time process such as reading and writing is performed, a head performing the process, a vibration amount of the head upon performing the process, and a process retry count in association with one another as vibration correspondence information. A process completion prediction time calculator calculates, upon determining a next execution command from among unexecuted read and write commands, process completion prediction time based on arrival time taken for a scheduled execution head to arrive at a scheduled process position from the current position, and a process retry count associated with the scheduled execution head and a current vibration amount thereof in the vibration correspondence information. A next execution command determining module determines the next execution command based on the process completion prediction time.

Abstract: In one embodiment, defects are detected on the face of a hard-disk drive platter. A preamble, a sync mark, user or pseudorandom data, and a data pad are written to every sector on a track of the platter. Inter-sector gaps that separate consecutive sectors are overwritten with a fixed data pattern such that consecutive sectors are in phase lock with one another. After the track has been written, the track is read back and analyzed. Consecutive sectors are analyzed continuously without stopping. The preambles, sync marks, data pads, and overwritten inter-sector gaps are analyzed using suitable flaw-scan techniques. The user or pseudorandom data is analyzed using both data-integrity checks and suitable flaw-scan techniques. This process is repeated for all tracks on the disk, and defect detection is completed when all tracks have been analyzed.

Abstract: An eccentricity measurement method of measuring the eccentricity of a rotary disk of a rotary encoder includes forming, on the rotary disk, at least one first straight-line pattern group in a different radial direction including a plurality of straight-line patterns that are equally spaced in the radial direction and extend in a normal line direction from a base point a predetermined distance away from a center of a radial scale of the rotary disk; placing the rotary disk on a table including at least one second straight-line pattern group including straight-line patterns; and measuring the amount and the direction of the eccentricity of the rotary disk in accordance with the position of the straight-line pattern of the first straight-line pattern group that coincides with the position of the straight line pattern of the second straight-line pattern group in the radial direction.

Abstract: According to one embodiment, a magnetic storage apparatus configured to write data to and read data from a magnetic medium with a head includes a setting module, a write module, a read module, and a quality measurement module. The setting module sets a plurality of sections divided in the track direction of the magnetic medium and a predetermined reference path along the track direction, and also sets at least one offset for each of the sections such that the offset is different between adjacent sections. The offset is the position of the head with respect to the reference path. The write module writes a first data pattern to the offset set by the setting module and writes a second data pattern to the reference path a predetermined number of times. The read module reads the first data pattern written by the write module. The quality measurement module measures the quality of the first data pattern read by the read module.

Abstract: A method and apparatus for measuring latency in a communication path is provided. The technique includes driving a signal such as a square wave on the communication path, such as a write path such that it travels around the write-read path, and sensing a returned signal at one end of the write-read path. A square wave signal corresponding to the square wave driven on the write path is delayed by a predetermined phase thus generating a delayed signal. The returned signal and the delayed signal are mixed, producing a mixed signal. The mixed signal is integrated to obtain an integrated output. The phase by which the delayed signal is shifted is successively adjusted. Returned signals are mixed with such delayed signals until the integrated output is equal to zero. The phase shift amount that results in a nulled integrated output, less a quarter cycle of the square wave, is equal to the round trip latency of the write-read path.

Abstract: Some embodiments of the present invention provide a system that characterizes the performance of a disk drive at frequencies in a set of frequencies in a frequency range. First, the disk drive is vibrated at each frequency in the set of frequencies, one frequency at a time. During this process, a disk drive performance metric is monitored. Next, the performance of the disk drive is characterized by determining the parameter related to acceleration due to the vibrations for each frequency at which a disk drive performance metric degrades by a predetermined amount from a baseline.

Abstract: A system includes a hard disk controller module configured to control a hard disk. A read channel device is in communication with the hard disk controller module via a read bus and a write bus. The read channel device includes a loopback circuit configured to selectively loop back the write bus to the read bus. The read channel is configured to generate a write clock for the hard disk controller module to write data on the write bus. The read channel is configured to generate a read clock for the hard disk controller module to read the data on the read bus. The write clock is independent of the read clock.

Abstract: A method for distinguishing unbalanced disc in an optical disc reproducing/recording apparatus, comprising following steps: moving an optical pickup head to a first position of an optical disc; rotating the optical disc to a predetermined rotating speed; transferring a focus error signal produced by the optical pickup head to a focus control voltage signal; controlling the optical pickup head by the focus control voltage signal to maintain a focus light spot produced by the optical pickup head on the optical disc; and distinguishing if the optical disc is an unbalanced disc according to the focus control voltage signal.