Magnetic disk drive and method for manufacturing a magnetic disk drive

Abstract

To accurately detect read errors in postcodes. [Solution] The magnetic disk device of the embodiment comprises a magnetic disk having a plurality of tracks, a magnetic head for reading and writing data to the magnetic disk, a plurality of servo regions provided on each of the plurality of tracks and including at least a portion of a first physical pattern which is the physical pattern after writing of a first data pattern including position information for each of the plurality of tracks, and a control unit for controlling the magnetic head. Each of the plurality of servo regions includes either a first servo region including the first physical pattern, or a second servo region including a second physical pattern which is the physical pattern after writing of a second data pattern different from the first data pattern, for each of the plurality of tracks, and the control unit determines whether the third servo region among the plurality of servo regions of the plurality of tracks has the first or the second physical pattern.

Description

[Technical Field]

[0001] Embodiments of the present invention relate to a magnetic disk device and a method for manufacturing a magnetic disk device. [Background technology]

[0002] In a magnetic disk drive, data is read and written by moving the magnetic head to a desired track position among multiple tracks on the magnetic disk. At this time, the magnetic head is aligned to the desired track according to magnetic head position correction information for each track, which is read from the postcode of each track.

[0003] However, invalid areas where no postcode is recorded may be mistakenly read as postcodes. In this case, the reading result of the invalid area, which does not contain meaningful information, may be judged as correct and used to align the magnetic head to the desired track, even though it cannot be used as magnetic head position correction information for each track. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] U.S. Patent Application Publication No. 2017 / 0263275 [Patent Document 2] U.S. Patent Application Publication No. 2021 / 0327468 [Overview of the project] [Problems that the invention aims to solve]

[0005] One embodiment aims to provide a magnetic disk device and a method for manufacturing a magnetic disk device that can accurately determine postcode read errors. [Means for solving the problem]

[0006] The magnetic disk device according to the embodiment includes a magnetic disk having a plurality of tracks, a magnetic head that reads and writes data to and from the magnetic disk, a plurality of servo areas provided respectively on the plurality of tracks and including at least a part of a first physical pattern which is a physical pattern after writing of a first data pattern including position information for each of the plurality of tracks, and a control unit that controls the magnetic head. The plurality of servo areas include, for each of the plurality of tracks, either a first servo area including the first physical pattern or a second servo area including a second physical pattern which is a physical pattern after writing of a second data pattern different from the first data pattern. The control unit determines which of the first and second physical patterns a third servo area has among the plurality of servo areas that the plurality of tracks have.

Brief Description of Drawings

[0007] [Figure 1] FIG. 1 is a schematic diagram showing an example of the configuration of a magnetic disk device according to the embodiment. [Figure 2] FIG. 2 is a schematic diagram showing an example of the configuration of a magnetic disk according to the embodiment. [Figure 3] FIG. 3 is a schematic diagram showing an example of a state in which servo data is written in a servo area according to the embodiment. [Figure 4] FIG. 4 is a diagram showing an example of a data pattern that a postcode of a magnetic disk according to the embodiment has. [Figure 5] FIG. 5 is a diagram showing an example of a data pattern that a base pattern of a magnetic disk according to the embodiment has. [Figure 6] FIG. 6 is a schematic diagram for explaining the positional relationship between a write head and a read head of a magnetic head according to the embodiment. [Figure 7] FIG. 7 is a schematic diagram showing the acquisition timing of a read waveform of a discrimination target area by the magnetic disk device according to the embodiment. [Figure 8]Figure 8 is a graph showing an example of various read waveforms of a magnetic disk according to the embodiment. [Figure 9] Figure 9 is a graph showing the distribution of correlation coefficients obtained from the read waveforms of the postcode or the background pattern written to the magnetic disk according to the embodiment. [Figure 10] Figure 10 is a flowchart showing an example of the procedure for postcode discrimination and error detection processing by a magnetic disk device according to the embodiment. [Figure 11] Figure 11 is a schematic diagram showing an example of a method for manufacturing a magnetic disk device according to an embodiment. [Figure 12] Figure 12 is a graph showing the distribution of frequency components obtained by discrete Fourier transform from the read waveform of the postcode or the read waveform of the background pattern written to the magnetic disk according to the embodiment. [Modes for carrying out the invention]

[0008] Embodiments of the present invention will be described in detail below with reference to the drawings. However, the present invention is not limited to the embodiments described below. Furthermore, the components in the embodiments described below include those that are easily conceivable by those skilled in the art or that are substantially the same.

[0009] (Example of a magnetic disk drive configuration) Figure 1 is a schematic diagram showing an example of the configuration of a magnetic disk device 1 according to an embodiment. The magnetic disk device 1 in this embodiment is configured as, for example, an HDD (Hard Disk Drive). However, the magnetic disk device 1 in this embodiment may be other types of magnetic disk devices, such as a hybrid HDD.

[0010] As shown in Figure 1, the magnetic disk device 1 of the embodiment includes a magnetic disk 10, a spindle motor (SPM) 11, a magnetic head 12, an arm 13, a voice coil motor (VCM) 14, a driver IC (Integrated Circuit) 20, a head amplifier IC 30, a memory 70, and a system controller 100.

[0011] The spindle motor 11 holds the magnetic disk 10 and rotates the magnetic disk 10 around a spindle (not shown). The magnetic disk 10 has a recording layer on which data can be recorded. More specifically, the magnetic disk 10 has multiple concentric tracks centered on the rotation center of the spindle motor 11, and data can be written to these tracks.

[0012] The magnetic head 12, which includes a write head and a read head (not shown), is mounted at the tip of an arm 13. The arm 13 is driven by a voice coil motor 14 connected to the other end, which moves the magnetic head 12 to a predetermined position on the magnetic disk 10. This brings the magnetic head 12 close enough to access the recording surface of the magnetic disk 10. In other words, this allows the magnetic head 12 to record (write) and read (reproduce) data on the recording surface of the magnetic disk 10.

[0013] The magnetic disk drive 1 may have a plurality of magnetic disks 10 held in parallel in the vertical direction on a spindle motor 11, and the recording surfaces of the magnetic disks 10 may be provided on both sides of the magnetic disks 10, for example. In this case, the magnetic disk drive 1 may have a plurality of magnetic heads 12 such that the number of magnetic heads 12 corresponds to the number of recording surfaces of the magnetic disks 10.

[0014] The system controller 100 is implemented using a large-scale integrated circuit (LSI), known as a System-on-Chip (SoC), in which multiple elements are integrated onto a single chip. The system controller 100 is connected to the host 200 and controls the entire magnetic disk drive 1 based on commands from the host 200. The host 200 is configured as, for example, a processor, a personal computer, or a server.

[0015] The system controller 100 includes a read / write (R / W) channel 40, a hard disk controller (HDC) 50, and a microprocessor (MPU) 60.

[0016] The R / W channel 40, HDC 50, and MPU 60 are electrically connected to each other, and the system controller 100 is electrically connected to the driver IC 20, head amplifier IC 30, and memory 70.

[0017] The R / W channel 40 is a signal processing circuit that processes read / write signals. The R / W channel 40 includes a read channel that performs signal processing for read data and a write channel that performs signal processing for write data (neither of which are shown). The read channel converts the read signal into digital data and demodulates the read data from the digital data. The write channel encodes the write data transferred from the HDC 50 and transfers the encoded write data to the head amplifier IC 30.

[0018] The HDC50 configures the interface between the magnetic disk drive 1 and the host 200 and performs read and write data transfer control. In other words, the HDC50 functions as a host interface controller that sends and receives signals to and from the host 200. Signals transferred from the host 200 include commands such as write commands and read commands. The HDC50 transmits these commands received from the host 200 to the MPU60.

[0019] In this manner, in response to various instructions from the host 200, the HDC 50 controls the writing of data to the magnetic disk 10 and the reading of data from the magnetic disk 10 via the magnetic head 12, head amplifier IC 30, R / W channel 40, and MPU 60.

[0020] The MPU60 is the main controller of the magnetic disk drive 1 and performs read / write (R / W) control via firmware. However, the MPU60 may also include a circuit for performing R / W control.

[0021] In R / W control, the MPU 60 controls data write and read operations according to commands from the host 200. More specifically, when the MPU 60 receives a write command from the host 200, for example, it executes a write operation to write data to a predetermined area of ​​the magnetic disk 10. Also, when the MPU 60 receives a read command from the host 200, for example, it executes a read operation to read data from a predetermined area of ​​the magnetic disk 10.

[0022] At this time, the MPU 60 controls the voice coil motor 14 via the driver IC 20 to position the magnetic head 12 at the desired position on the magnetic disk 10 and perform a write or read operation.

[0023] The driver IC 20 controls the driving of the spindle motor 11 and the voice coil motor 14 according to the control of the MPU 60. When the spindle motor 11 is driven, the magnetic disk 10 held by the spindle motor 11 rotates as described above. When the voice coil motor 14 is driven, the magnetic head 12 is positioned on the target track on the magnetic disk 10.

[0024] The head amplifier IC 30 supplies a write signal to the magnetic head 12 corresponding to the write data supplied from the R / W channel 40. The head amplifier IC 30 also amplifies the read signal output from the magnetic head 12 and transmits it to the R / W channel 40.

[0025] The memory 70 is composed of volatile memory and non-volatile memory, etc. As an example, the memory 70 includes a buffer memory consisting of DRAM (Dynamic Random Access Memory) and flash memory.

[0026] (Example of magnetic disk configuration) Figure 2 is a schematic diagram showing an example of the configuration of the magnetic disk 10 according to the embodiment.

[0027] As shown in Figure 2, the magnetic disk 10 has multiple tracks TR arranged concentrically, defined by servo data pre-written to the magnetic disk 10. Figure 2 also shows an example of the rotation direction of the magnetic disk 10. However, the rotation direction of the magnetic disk 10 may be the opposite of the example in Figure 2.

[0028] Furthermore, the magnetic head 12 moves relative to the magnetic disk 10 as the magnetic disk 10 rotates. Therefore, the write / read direction, that is, the direction in which data is written or read by the magnetic head 12, is along the circumferential direction of the magnetic disk 10 and opposite to the direction of rotation of the magnetic disk 10.

[0029] Furthermore, in the radial direction, the direction from the edge of the magnetic disk 10 toward the center is sometimes called the inner diameter (ID) direction, and the direction from the center of the magnetic disk 10 toward the edge is sometimes called the outer diameter (OD) direction.

[0030] Multiple tracks TR are provided with multiple servo regions SV (SVn, SVs) arranged radially in the radial direction with predetermined intervals in the circumferential direction, and data regions DA positioned between them.

[0031] In at least a portion of the servo area SV, servo data used for positioning the magnetic head 12 during the manufacturing process of the magnetic disk device 1 is written. At this time, the servo area SV may include a servo area SVn and a servo area SVs, depending on the amount of information written. The servo area SVn is an area to which a predetermined amount of information data is written, and the servo area SVs is an area to which the same or lesser amount of information data as the servo area SVn is written.

[0032] As a result, at least one servo region SVs is placed between two circumferentially adjacent servo regions SVn. In the example in Figure 2, one servo region SVs is placed between adjacent servo regions SVn. That is, servo regions SVn and servo regions SVs are arranged alternately, one at a time, in the circumferential direction. However, servo regions SVn may be placed instead of servo regions SVs, regardless of the example in Figure 2.

[0033] The data area DA of the magnetic disk 10 is used to write user data received from the host 200, metadata such as error correction codes associated with the user data, and system data.

[0034] In this specification, a track TR on which servo data is written will be referred to as a servo track, and a track TR on which user data, etc., is written will be referred to as a data track, and these will be distinguished from each other.

[0035] That is, servo data included in the servo area SV described above holds in advance the setting of the positional relationship between a plurality of servo tracks and a plurality of data tracks. Thereby, the magnetic disk device 1 can execute positioning control to position the magnetic head 12 on a target data track based on the servo data recorded on each servo track. The positioning control includes a seek operation to move the magnetic head 12 in the radial direction toward the target data track, a tracking operation to maintain the magnetic head 12 on the target data track, and the like.

[0036] FIG. 3 is a schematic diagram showing an example of a state in which servo data is written in the servo area SV according to the embodiment.

[0037] In FIG. 3, three tracks TR n+1 , n-1 , , n ,

[0039] , , n , , n+1 , n-1 ,

[0038] , TR n , TR n+1 adjacent to each other in the radial direction of the magnetic disk 10 and the track centers C n-1 , TR <00000​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​As shown in Figure 3, the servo region SVn of each track TR contains the preamble, servo mark, Gray code, N burst, and Q burst in this order in the write / read direction, i.e., in the circumferential direction of the magnetic disk 10. In addition, in at least some tracks TR, the postcode is recorded in the region following the Q burst in the write / read direction.

[0040] These servo data, including preambles, servo marks, Gray codes, N-bursts, Q-bursts, and postcodes, are recorded such that their respective circumferential start and end positions are radially aligned between individual tracks TR.

[0041] The preamble is a single-period pattern data where the data value changes periodically in the circumferential direction. The magnetic head 12 reads the servo waveform, and the R / W channel 40 captures the read servo waveform as sampled data based on the servo clock. The preamble is used to adjust the amplitude, phase, and frequency of the sampled data.

[0042] A servo mark is pattern data used to determine the demodulation timing of servo data. Based on the detection timing of the servo mark, the MPU 60 determines the demodulation timing of the various servo data read by the magnetic head 12 thereafter.

[0043] Gray code is pattern data that includes addresses for identifying each servo track on the magnetic disk 10.

[0044] N-bursts and Q-bursts are pattern data used to detect the amount of displacement of the servo track from the track center, indicated by the address contained in the Gray code, and to calculate the position error signal required for track tracking.

[0045] More specifically, N-bursts, like the preamble, servo marks, and Gray code, have a radial center position that corresponds to the individual track TRn-1 ,TR n ,TR n+1 Each of the track centers C n-1 ,C n ,C n+1 It is positioned to coincide with the individual track TR. On the other hand, the Q-burst has its radial center position aligned with the individual track TR. n-1 ,TR n ,TR n+1 Each of the track centers C n-1 ,C n , n+1 They are positioned with a 0.5 SvTp offset. The N-burst and Q-burst are positioned so that the phase of the data pattern is reversed by 180 degrees by 1 SvTp in the radial direction. Reversing the phase of the data pattern by 180 degrees means that if the written data is a binary value of "0" and "1", the data pattern will have "0" and "1" swapped.

[0046] By configuring the N-burst and Q-burst in this way, the magnetic head 12 can perform the individual track TR n-1 ,TR n ,TR n+1 Each of the track centers C n-1 ,C n ,C n+1 When passing through, and Track Center C n-1 ,C n ,C n+1 When passing through a position offset by 0.5 SvTp, the maximum and minimum amplitudes of the N-burst lead waveform and the Q-burst lead waveform swap.

[0047] The MPU60 can detect the amount of displacement of the servo track from the track center based on the amplitude and phase of the N-burst read waveform and the amplitude and phase of the Q-burst read waveform.

[0048] Furthermore, as mentioned above, Q Burst is used by individual track TR n-1 ,TR n ,TR n+1 Each of the track centers C n-1 ,Cn , n+1 Because it is recorded with a 0.5 SvTp shift, the servo data, including the preamble, servo mark, Gray code, N burst, Q burst, and postcode, will have a radial pitch of 0.5 SvTp.

[0049] The postcode is pattern data that encodes the RRO correction amount. RRO (Repeatable Run Out) is a positional deviation that occurs repeatedly in sync with the rotation of the magnetic disk 10.

[0050] Although the ideal shape of the track is a perfect circle, distortion occurs in the servo track due to vibrations received during servo data writing and the quality of servo data writing. Therefore, the radial position of the servo track, as determined by the N-burst and Q-burst described above, may deviate from the radial position of an ideally shaped servo track. This positional deviation occurs repeatedly by the same amount with a period of one rotation of the magnetic disk 10, and is therefore called RRO (Rapid Error Relief).

[0051] In the manufacturing process of the magnetic disk drive 1, the RRO correction amount is measured for each predetermined servo track and written as a postcode to the corresponding servo area SVn.

[0052] The MPU60 obtains the radial position of the magnetic head 12, which is obtained by reading the N-burst and Q-burst, by applying a correction using the RRO correction amount recorded in the postcode, thereby canceling out the positional shift caused by RRO.

[0053] The postcode is overwritten on the background pattern that is pre-lit in the circumferentially adjacent areas of the Q burst in each track TR. In some track TRs where the postcode was not lit, the background pattern remains without being overwritten. In the example in Figure 3, the track TR n-1 ,TR n ,TR n+1 Among them, Truck TRn-1 ,TR n The postcode is recorded in the track TR n+1 The underlying pattern remains.

[0054] Thus, tracks TR in which the postcode is not written and the underlying pattern remains are invalid tracks, etc., that have defects or other issues and were determined to be unsuitable for data writing / reading during the manufacturing process of the magnetic disk device 1.

[0055] The background pattern may be lit only in a portion of the circumferential region of the area used for recording the postcode, or it may be lit over the entire circumferential region of the area used for recording the postcode, or it may be lit beyond the area used for recording the postcode. Therefore, the respective circumferential end positions of the background pattern and the postcode do not necessarily coincide radially between individual tracks TR. However, the respective circumferential start positions of the background pattern and the postcode are recorded so that they coincide radially between individual tracks TR.

[0056] In the example in Figure 3, the background pattern is written only to a portion of the circumferential area of ​​the region used for recording the postcode. In this case, the area following the remaining background pattern may be a blank area BNK where no predetermined information is written. In other words, a blank area BNK is an area that does not contain meaningful information.

[0057] Furthermore, the postcode written to the servo area SVn may include a Sync mark indicating the starting position of the postcode, and parity bits for detecting data errors such as corrupted data bits contained in the postcode.

[0058] In the servo regions SVs of each track TR, N-bursts and Q-bursts are recorded in that order along the write / read direction. In other words, the servo regions SVs contain the servo data written to the servo region SVn described above, excluding the preamble, servo mark, Gray code, and postcode. Therefore, the circumferential length of the servo regions SVs is shortened compared to the servo region SVn, and as a result, it is possible to increase the amount of user data that can be recorded in the data region DA.

[0059] Thus, since no servo marks are recorded in the servo region SVs, the R / W channel 40 determines the demodulation timing of various servo data based on the timing at which a servo mark is detected when the magnetic head 12 passes over another servo region SVn. However, in addition to bursts and Q-bursts, an additional pattern for detecting a shift in demodulation timing may be written to the servo region SVs. Also, a preamble, servo marks, and Gray code may be written to the servo region SVs, similar to the servo region SVn.

[0060] As described above, the servo region SVn contains the preamble, servo mark, Gray code, N-burst, Q-burst, and postcode, and this data written to the servo region SVn is also called normal servo data. In addition, the servo region SVs contains only burst and Q-burst, and this data written to the servo region SVs is also called short servo data.

[0061] Next, an example of the configuration of the background pattern of the magnetic disk 10 of the embodiment will be described using Figures 4 and 5. The postcode and the background pattern described above are written with different data patterns.

[0062] Figure 4 shows an example of a data pattern of the postcode of the magnetic disk 10 according to the embodiment.

[0063] One servo data is represented, for example, by "0" and "1". If the unit of the write length of the servo data to the magnetic disk 10 is T, then the write length of one servo data is 4T. More specifically, the R / W channel 40 of the magnetic disk device 1 has a fundamental frequency set for writing and reading the servo data. If the unit of the fundamental frequency is FreqRWC, then 1T corresponds to the time of one cycle, that is, the time expressed as the reciprocal of the fundamental frequency (1 / FreqRWC).

[0064] As shown in Figure 4, when one servo data is written to the magnetic disk 10, it is converted into 4T length data. More specifically, servo data "0" is converted to, for example, "0011", and servo data "1" is converted to, for example, "1100".

[0065] The data included in the above postcode is also represented by a combination of servo data "0" and servo data "1". Figure 4 shows examples of when two servo data such as "00", "01", "10", and "11" are converted to 8T length data, and when three servo data such as "000", "001", "010", "100", "011", "101", "110", and "111" are converted to 12T length data.

[0066] In the following, the servo data before it is written to the magnetic disk 10, and the pattern represented by "0"s and "1"s in the converted data, will be called the data pattern, and the data pattern that has been written to the magnetic disk 10 and physically exists on the magnetic disk 10 will be called the physical pattern. In this case, the data read by the magnetic head 12 from the physical pattern after it has been written to the magnetic disk 10, and the data before it is converted back into servo data, can also be called the data pattern. However, sometimes the converted servo data before it is written to the magnetic disk 10 and the pre-conversion servo data read by the magnetic head 12 are distinguished and referred to as servo write data and servo read data, respectively.

[0067] As can be seen in Figure 4, the converted postcode is represented by a combination of 2T or 4T data patterns: “00”, “11”, “0000”, and “1111”.

[0068] As mentioned above, the background pattern overwritten with the postcode has a different data pattern from the postcode. That is, the background pattern is composed without including the 2T or 4T data patterns of "00", "11", "0000", and "1111".

[0069] Figure 5 shows an example of a data pattern on the background pattern of the magnetic disk 10 according to the embodiment.

[0070] Example 1 in Figure 5 is an example of constructing a base pattern data pattern by repeating data with a light length of 3T, consisting of "000" and "111". Example 2 in Figure 5 is an example of constructing a base pattern data pattern by repeating data with a light length of 5T, consisting of "00000" and "11111". Example 3 in Figure 5 is an example of constructing a base pattern data pattern by repeating data with a light length of 6T, consisting of "000000" and "111111".

[0071] Note that data patterns in which the same data value is repeated consecutively, such as "00", "11", "0000", and "1111" in the postcode, or "000", "111", "00000", "11111", "000000", and "111111" in the background pattern, are examples of sub-data patterns included in the background pattern. Also, the light lengths such as 2T, 3T, 4T, etc. that a sub-data pattern has are sometimes called the pattern length of the sub-data pattern.

[0072] Thus, the base pattern can be constructed by combining sub-data patterns with light lengths other than 2T or 4T. Another example is that the base pattern can also be constructed by combining sub-data patterns with different light lengths other than 2T or 4T.

[0073] Example 4 in Figure 5 is an example of constructing the background pattern data pattern by repeating a data set, where one set consists of a sub-data pattern with a light length of 8T, combining a sub-data pattern with a light length of 3T for "000" and a sub-data pattern with a light length of 5T for "11111". Example 5 in Figure 5 is an example of constructing the background pattern data pattern by repeating a data set, where one set consists of a sub-data pattern with a light length of 12T, combining a sub-data pattern with a light length of 3T for "000" and "111" and a sub-data pattern with a light length of 6T for "111111".

[0074] By configuring the background pattern as described above, it is possible to obtain a background pattern having a data pattern that does not include any of the 2T or 4T sub-data patterns of "00", "11", "0000", and "1111" included in the postcode.

[0075] In order to improve the positioning accuracy of the magnetic head 12, it is preferable that the postcode indicating the RRO correction amount is written corresponding to the write position and read position of all data tracks.

[0076] However, in light of the manufacturing efficiency of the magnetic disk drive 1, postcodes may be written only to correspond to the write position of the data track, for example, to the read position. In such a configuration, when aligning the read head of the magnetic head 12, the RRO correction amount of the magnetic head 12 may be controlled based on the postcode written to correspond to a nearby write position. This is because, during data reading, the read head of the magnetic head 12 is aligned to the read position, and the corresponding postcode is not written to the read position.

[0077] For example, whether the postcode of a predetermined write position can be read from a read position during data reading is determined by whether the read position at that time matches a predetermined write position on a different data track from the data track to which the read position belongs, or whether these read and write positions are within a predetermined distance of each other. If these read and write positions match or are within a predetermined distance of each other, the MPU60 determines that the postcode of the write position being determined can be read from the read position at that time.

[0078] As described above, the ability to read a postcode at a predetermined light position during reading is due to the configuration of the magnetic head 12 and the driving operation of the arm 13 on which the magnetic head 12 is mounted.

[0079] Figure 6 is a schematic diagram illustrating the positional relationship between the write head 12w and the read head 12r of the magnetic head 12 according to this embodiment.

[0080] As shown in Figure 6, the light head 12w and the read head 12r of the magnetic head 12 are provided on the magnetic head 12, spaced apart from each other, for example, in a direction along the extension direction of the arm 13. The magnetic head 12 is moved to a desired read position or write position by the rotational drive of the arm 13.

[0081] As a result, the light head 12w and the read head 12r can be positioned on different tracks TR depending on the rotation angle of the arm 13, that is, depending on the radial position of the destination of the magnetic head 12. Therefore, when the read head 12r is at a predetermined read position on a predetermined track TR, the light head 12w can be positioned at a predetermined light position on another track TR. In this case, the read head 12r at the predetermined read position may be able to read the postcode corresponding to a predetermined light position on the other track TR.

[0082] As described above, when a readable postcode is available during data reading, etc., the RRO correction amount can be read from that postcode and used to correct the read position of the magnetic head 12, thereby improving the positioning accuracy of the magnetic head 12 during reading in the magnetic disk drive 1.

[0083] However, as mentioned above, among the multiple tracks TR, there may be parts where the postcode is not written to the servo area SVn, such as invalid tracks, and the underlying pattern remains. Therefore, even if there is an area used for writing the postcode within the range readable from the read position during data reading, it is necessary to determine whether what is written to that area is the postcode or the underlying pattern that remained without the postcode being written.

[0084] (Example of postcode detection operation) Next, using Figures 7 to 9, the operations performed in the magnetic disk device 1 of the embodiment to distinguish between the postcode and the background pattern will be described. In the following description, the area used for writing the postcode, which is within the range readable from the read position during data reading, etc., will be referred to as the area to be distinguished.

[0085] The MPU60 first acquires the read waveform of the region to be analyzed. The timing of acquiring this read waveform is shown in Figure 7.

[0086] Figure 7 is a schematic diagram showing the timing of acquiring the read waveform of the area to be discriminated by the magnetic disk device 1 according to the embodiment.

[0087] As shown in Figure 7, when acquiring the read waveform of the region to be discriminated, the MPU 60 transmits a read gate signal RGS to the R / W channel 40, which indicates the start and end timings of the read operation. The R / W channel 40 starts reading when the read gate signal RGS reaches a "H" level and ends reading when it reaches a "L" level. While the read gate signal RGS is at a "H" level, the read waveform is sampled at the fundamental frequency (FreqRWC) interval described above.

[0088] Furthermore, in the servo region SVn which includes the region to be discriminated, the magnetic head 12 moving in the write / read direction shall pass the end position of the servo mark at time t1 and the start position of the region to be discriminated at time t2. Also, if a postcode is written to the region to be discriminated, the magnetic head 12 shall pass the end position of that postcode at time t4.

[0089] Furthermore, as shown in the example in Figure 7, if the end position of the background pattern is before the end position of the postcode in the write / read direction, and the background pattern is what is being written to the area to be identified, the magnetic head 12 will pass the end position of the background pattern at time t3, prior to time t4.

[0090] In this case, regardless of whether the area to be determined is the postcode or the background pattern, if the time range is from t2 to t3, it is possible to obtain a partial read waveform of the postcode, or a partial or complete read waveform of the background pattern.

[0091] In the example shown in Figure 7, within the time range of t2 to t3, the lead gate signal RGS is set to a "H" level at time t21, which is delayed by dly time from time t2, and the lead gate signal RGS is set to a "L" level at time t22, which is len time from time t21, and the lead gate signal RGS is set to a "L" level, which ends the read. By appropriately adjusting the dly time and len time, it is possible to acquire a read waveform in any region of the postcode or background pattern, thereby improving the accuracy of distinguishing between the postcode and the background pattern.

[0092] Furthermore, the timing for acquiring the read waveform of the region to be discriminated can be set separately from the timing for acquiring the read waveform when reading the RRO correction amount from the postcode.

[0093] Figure 8 shows the read waveform obtained as described above, specifically the read waveform when a postcode is written to the region to be identified, and the read waveform when a background pattern is written, along with the theoretical waveform of the background pattern.

[0094] Figure 8 is a graph showing an example of various read waveforms of the magnetic disk 10 according to the embodiment.

[0095] More specifically, Figure 8(a) shows the theoretical waveform of the data pattern that will be written as the background pattern, Figure 8(b) shows a partial excerpt of the read waveform of the background pattern where the postcode remained without being overwritten, and Figure 8(c) shows a partial excerpt of the read waveform of the postcode that was overwritten onto the background pattern. The horizontal axis of each graph represents the sampling time, and the vertical axis represents the amplitude of each waveform. The amplitude on the vertical axis is negative when reading a region where "0" is written, and positive when reading a region where "1" is written.

[0096] Note that the waveforms in Figures 8(a) and 8(b) are examples where the background pattern has a repeating data pattern of "000" and "111".

[0097] As shown in Figure 8(a), a background pattern with a repeating data pattern of light length 3T theoretically results in a waveform that repeats maxima and maxima at a constant period.

[0098] As shown in Figure 8(b), the read waveform of the background pattern actually written to the magnetic disk 10 is similar to the waveform in Figure 8(a), although the regularity is slightly disrupted compared to Figure 8(a).

[0099] Thus, the read waveform of the actually written background pattern will differ slightly from the theoretical waveform of the background pattern due to the influence of factors such as the quality of the magnetic disk 10 and the write or read accuracy of the magnetic head 12.

[0100] As shown in Figure 8(c), the postcode written to the magnetic disk 10 also exhibits multiple variations in amplitude values, unlike the waveform in Figure 8(a), which has only two amplitude values, such as a maximum and a minimum. However, even taking this into consideration, the postcode has a data pattern in which "00", "11", "0000", and "1111", which are not included in the background pattern, are arbitrarily combined. Therefore, the postcode read waveform shown in Figure 8(c) does not resemble either of the waveforms in Figures 8(a) or 8(b).

[0101] To compare the waveforms in Figures 8(a) to 8(c) more quantitatively, for example, the correlation coefficient between the waveform in Figure 8(a) and the waveform in Figure 8(b), and the correlation coefficient between the waveform in Figure 8(a) and the waveform in Figure 8(c), can be calculated and the results of these correlation coefficients can be referenced.

[0102] There are various types of correlation coefficients, but here we will not specify the method of calculating the correlation coefficient. As an example, the formula for Pearson's product-moment correlation coefficient is shown in equation (1) below.

number

[0103] The correlation coefficient between the waveform in Figure 8(a) and the waveform in Figure 8(b) is calculated based on equation (1) above, for example, assuming that the waveform in Figure 8(a) is represented by the variable x and the waveform in Figure 8(b) is represented by the variable y.

[0104] The correlation coefficient between the waveform in Figure 8(a) and the waveform in Figure 8(c) is calculated based on equation (1) above, for example, assuming that the waveform in Figure 8(a) is represented by the variable x and the waveform in Figure 8(c) is represented by the variable y.

[0105] The calculated values ​​of various correlation coefficients, including Pearson's product-moment correlation coefficient mentioned above, range from -1 to +1. A correlation coefficient closer to -1 indicates a strong negative correlation, while a correlation coefficient closer to +1 indicates a strong positive correlation. Furthermore, a correlation coefficient closer to 0 means there is no correlation between the two variables x and y.

[0106] Figure 9 is a graph showing the distribution of correlation coefficients obtained from read waveforms read from postcodes or background patterns written to the servo region SVn of the magnetic disk 10 according to the embodiment.

[0107] In Figure 9, the horizontal axis of the graph represents the correlation coefficient, and the vertical axis represents the theoretical occurrence rate of the background pattern in the read waveforms of the postcode or background pattern. Furthermore, the data group Dp plotted on the left side of the graph is based on the read waveforms of the postcode, while the data group Dg plotted on the right side of the graph is based on the read waveforms of the background pattern.

[0108] The occurrence rate of the underlying pattern in the postcode read waveform is, more specifically, the number of occurrences of a data pattern that matches the theoretical waveform of the underlying pattern in the read waveforms acquired multiple times for the postcode written to the magnetic disk 10. Similarly, the occurrence rate of the underlying pattern in the read waveform is the number of occurrences of a data pattern that matches the theoretical waveform of the underlying pattern in the read waveforms acquired multiple times for the underlying pattern written to the magnetic disk 10.

[0109] In other words, for example, suppose that among the read waveforms obtained multiple times for a postcode, the number of data points with a correlation coefficient of -0.1 is 1000, and the occurrence rate at that time is 0.032. In this case, it means that among the 1000 read waveforms of the postcode that showed a correlation coefficient of -0.1, the data pattern that matches the theoretical waveform of the underlying pattern appeared 32 times.

[0110] Furthermore, for example, suppose that among the read waveforms acquired multiple times for a base pattern, the number of data points for a read waveform with a correlation coefficient of 0.7 is 1000, and the occurrence rate at that time is 0.046. In this case, it means that out of the 1000 read waveforms of the base pattern that showed a correlation coefficient of 0.7, the data pattern that matched the theoretical waveform of the base pattern appeared 46 times.

[0111] As shown in Figure 9, when we examine the results of the correlation coefficient calculation based on the above, we find that all of the data group Dp based on the postcode read waveforms are distributed at positions where the correlation coefficient is less than 0 and close to 0. From this, it can be said that the postcode read waveforms have almost no correlation with the theoretical waveform of the underlying pattern.

[0112] On the other hand, all of the data sets Dg based on the read waveforms of the background pattern have correlation coefficients greater than 0 and are distributed close to a correlation coefficient of +1. From this, it can be said that the read waveforms of the background pattern written to the magnetic disk 10 are positively correlated with the theoretical waveform of the background pattern.

[0113] Furthermore, since the distributions of data group Dp and data group Dg are separate and do not overlap, it can be seen that, based on the read waveform of the target region acquired as described above, it is possible to determine whether what is written to the target region is a postcode or an underlying pattern.

[0114] More specifically, during the manufacturing of the magnetic disk drive 1, the read waveform of the background pattern before the postcode is overwritten and the read waveform of the postcode after the overwrite are obtained in advance from the magnetic disk 10. Furthermore, a correlation coefficient is calculated based on these read waveforms, and a threshold value that serves as the basis for the above determination can be set based on the distribution of the data group Dp based on the postcode read waveform and the distribution of the data group Dg based on the background pattern read waveform. The set threshold value is stored, for example, in the MPU 60 of the magnetic disk drive 1.

[0115] In this case, if the magnetic disk device 1 has multiple magnetic disks 10, the above measurement can be performed on one or more magnetic disks 10 that are arbitrarily selected from among those magnetic disks 10, and a threshold can be set for each magnetic disk device 1. Alternatively, the above measurement may be performed on all magnetic disks 10 that are provided in a single magnetic disk device 1, in which case a threshold can be set for each individual magnetic disk 10.

[0116] When reading predetermined data, if a determination is made regarding the discriminant area that can be read from the read position, the MPU60 acquires the read waveform of the discriminant area at the read timing shown in Figure 7 above, calculates the correlation coefficient with the theoretical waveform of the background pattern, and makes a determination regarding that discriminant area based on the preset threshold.

[0117] In the example graph in Figure 9, for example, the threshold TH can be set to 0.15. In this case, if the correlation coefficient based on the read waveform of the area to be discriminated is less than 0.15, it can be determined that what is written to that area is a postcode. On the other hand, if the correlation coefficient based on the read waveform of the area to be discriminated is 0.15 or greater, it can be determined that what is written to that area is a background pattern and not a postcode.

[0118] (Example of postcode detection process) Next, using Figure 10, an example of postcode discrimination processing and error detection processing in the magnetic disk device 1 of the embodiment will be described. Figure 10 is a flowchart showing an example of the procedure for postcode discrimination processing and error detection processing by the magnetic disk device 1 according to the embodiment.

[0119] As shown in Figure 10, the MPU 60 uses the R / W channel 40 to acquire the read waveform of the region to be discriminated (step S101). The MPU 60 calculates the correlation coefficient between the read waveform of the region to be discriminated and the theoretical waveform of the background pattern (step S102). The MPU 60 determines whether the calculated correlation coefficient is less than a preset threshold (step S103).

[0120] If the correlation coefficient based on the read waveform is below the threshold (step S103: Yes), it can be said that what is written to the region to be determined is a postcode. Then, the MPU60 acquires data regarding the quality of that postcode (step S104). Examples of postcode quality data include the detection result of the Sync mark indicating the starting position of servo data such as postcodes, and the error judgment result based on the parity bit for error detection attached to the servo data including postcodes.

[0121] The MPU60 performs a quality determination of the postcode based on the acquired postcode quality data (step S105).

[0122] If the quality of the postcode is within an acceptable range (step S105: Yes), the MPU 60 obtains the playback position of the postcode (step S106). The playback position of the postcode is calculated by the MPU 60 based on the distance between the current position of the magnetic head 12, which has been moved to the read position of the read target portion on the magnetic disk 10, and the position of the postcode that was determined above. The current position of the magnetic head 12 can be obtained by reading the servo data corresponding to the read position at that time.

[0123] The MPU60 determines whether the playback position of the acquired postcode is within the appropriate range (step S107). At this time, if the distance between the current position of the magnetic head 12 and the postcode is within the distance at which the postcode can be read, it is determined that the playback position of the postcode is within the appropriate range; if it exceeds the distance at which the postcode can be read, it is determined that the playback position of the postcode is not within the appropriate range.

[0124] If the playback position of the postcode is within the appropriate range (step S107: Yes), the MPU 60 corrects the read head position of the magnetic head 12 based on the RRO correction amount read from the postcode (step S108), and then performs postcode determination processing (step S110). Postcode determination processing is, for example, data reading processing for desired data.

[0125] If the correlation coefficient calculated from the read waveform of the area to be determined is above a threshold (Step S103: No), if the quality of the postcode is not within an acceptable range (Step S105: No), or if the playback position of the postcode is not within an appropriate range (Step S107: No), the MPU 60 determines an error (Step S109). In this case, there is no postcode available for read position correction of the magnetic head 12, so processing after postcode determination is performed without read head position correction of the magnetic head 12 (Step S110). Processing after postcode determination is, for example, data read processing for the desired data.

[0126] With the above steps completed, the postcode determination process and error detection process by the magnetic disk device 1 according to the embodiment are finished.

[0127] (Method of manufacturing a magnetic disk drive) Next, a method for manufacturing the magnetic disk device 1 will be described using Figure 11. Figure 11 is a schematic diagram showing an example of a method for manufacturing the magnetic disk device 1 according to an embodiment.

[0128] The manufacturing method of the magnetic disk device 1 includes the process of writing various types of information, such as servo data, to the magnetic disk 10. The following description will mainly focus on the above-mentioned writing process to the magnetic disk 10 in the manufacturing method of the magnetic disk device 1.

[0129] The writing of various types of information, including servo data, to the magnetic disk 10 is performed, for example, after the magnetic disk drive 1 has been assembled.

[0130] As shown in Figure 11(a), the servo area SVn of the magnetic disk 10 is first written with servo data excluding the postcode, such as the preamble, servo mark, Gray code, N burst, and Q burst. In addition, the area used for writing the postcode is written with a background pattern.

[0131] In other words, the magnetic disk 10 is written in the following order in the write / read direction: preamble, servo mark, Gray code, N burst, Q burst, and background pattern.

[0132] As described above, the background pattern is lit from the starting position of the area used for writing the postcode to a range less than or equal to the length of that area. If the length of the background pattern is shorter than the length of the area used for writing the postcode, the area after the end of the background pattern may be a blank area (BNK).

[0133] Furthermore, servo data such as N-bursts and Q-bursts are written to the servo area SVs of the magnetic disk 10 at the same timing as the servo area SVn. If an additional pattern for detecting demodulation timing deviations is added to the servo data in the servo area SVs as described above, a data pattern similar to the background pattern described above may be written to the area used to write the additional pattern. Alternatively, the background pattern written to the servo area SVs may be different from the data pattern of the background pattern written to the servo area SVn. In addition, the data pattern written to the servo area SVs may include the preamble, servo marks, and Gray code written to the servo area SVn.

[0134] After writing this servo data, etc., the RRO correction amount is learned. In the RRO correction amount learning, a predetermined track is sequentially set as the target track for each track within a predetermined range, and for each target track, the difference between the actual radial position of the magnetic head 12 and the radial position of the target track is measured under positioning control based on Gray code, N burst, and Q burst.

[0135] In other words, the MPU60 reads the Gray code, N burst, and Q burst written to the servo region SVn and estimates the position of the magnetic head 12 based on these read results. The MPU60 also positions the magnetic head 12 on the target track based on the estimated position of the magnetic head 12. Meanwhile, the MPU60 obtains the deviation of the estimated position of the magnetic head 12 from the target track as the RRO correction amount.

[0136] As shown in Figure 11(b), the MPU 60 writes the RRO correction amount obtained as described above to the postcode area of ​​the servo region SVn in at least some of the tracks among the multiple tracks on the magnetic disk 10. At this time, the background pattern is overwritten on the tracks that are targeted for postcode writing. On the other hand, on tracks that are not targeted for writing, such as those designated as invalid tracks, the postcode is not written, and the background pattern remains in the servo region SVn.

[0137] Furthermore, in at least one of the magnetic disks 10 incorporated in the magnetic disk device 1, the read waveform of the background pattern and the read waveform of the postcode are acquired before and after writing the postcode to the servo area SVn, and a threshold value is set to be used to distinguish between the postcode and the background pattern.

[0138] Based on the above, the magnetic disk device 1 of the embodiment is manufactured.

[0139] (Overview) In magnetic disk drives, a postcode containing RRO correction amount information may be written only to the write position of the data track on the magnetic disk, corresponding to the write position. In such magnetic disk drives, the postcode corresponding to a predetermined write position may be used to correct the read position of the magnetic head during data reading, etc. However, in this case, there is a risk of mistakenly identifying the read result of a servo area where the postcode has not been written as data read from the postcode.

[0140] Here, when using a postcode corresponding to a predetermined write position during data reading, for example, a determination is made as to whether the quality of the postcode is within an acceptable range, and whether the reproduction position of the postcode is within an appropriate range.

[0141] However, even if the postcode playback position is within the correct range, it is impossible to determine whether the read result intended for magnetic head read position correction is actually data read from the postcode. Furthermore, during postcode quality evaluation, even in servo areas where the postcode is not written, some signal may be mistakenly identified as a Sync mark detection signal. Even if parity bits are added to the servo data, not all errors can be detected; for example, odd-numbered data bit corruptions can be detected, but even-numbered ones cannot. Increasing the amount of information in the parity bits used for error detection to improve the accuracy of error detection in the servo data would reduce the amount of user data that can be recorded in the data area DA.

[0142] According to the magnetic disk device 1 of the embodiment, each of the multiple servo regions SVn includes, for each of the multiple tracks, either a servo region SVn on which a data pattern indicating a postcode is written, or a servo region SVn on which a background pattern having a data pattern different from the postcode data pattern is written.

[0143] As described above, the background pattern that is lit in a predetermined servo region SVn is one that has been lit before the postcode is lit and remains lit without the postcode being lit. In this way, by pre-lighting a background pattern that has a data pattern different from the postcode's data pattern, it is possible to determine whether it is a postcode or a background pattern that is lit in a predetermined servo region SVn.

[0144] This reduces the likelihood of misidentifying the background pattern as a postcode, allowing for highly accurate detection of postcode read errors. In addition to evaluating the quality and regeneration position of the postcode, the system also evaluates the distinction between the postcode and the background pattern, thus expanding the acceptable range for the regeneration position of the postcode. Consequently, the frequency of position correction of the magnetic head 12 during data reading and other operations can be increased, improving the positioning accuracy of the magnetic head 12.

[0145] According to the magnetic disk device 1 of this embodiment, the background pattern has a sub-data pattern different from the sub-data pattern of the postcode. This makes it possible to differentiate the data pattern of the background pattern from the data pattern of the postcode so that the postcode and the background pattern can be distinguished.

[0146] According to the magnetic disk device 1 of the embodiment, the MPU 60 determines the degree of agreement between the read waveform of the area to be discriminated and the read waveform of the background pattern based on the correlation coefficient between the read waveform of the area to be discriminated and the read waveform of the background pattern. By performing the evaluation using the correlation coefficient in this way, the degree of agreement between these read waveforms can be quantitatively determined, and the accuracy of the determination can be improved.

[0147] In the above embodiment, the correlation coefficient between the read waveform of the area to be discriminated and the theoretical waveform of the underlying pattern was calculated to determine whether or not a postcode was written to the area to be discriminated. However, the above determination may also be made by calculating the correlation coefficient between the read waveform of the area to be discriminated and, for example, the read waveform of the underlying pattern actually written to the magnetic disk 10.

[0148] In this case, the read waveform of the background pattern can be one that was acquired in advance during the manufacturing of the magnetic disk drive 1. Furthermore, the threshold used for the above determination can also be set based on, for example, the correlation coefficient between the postcode read waveform and the background pattern read waveform acquired during the manufacturing of the magnetic disk drive 1.

[0149] The correlation coefficient between the postcode read waveform and the background pattern read waveform is also expected to be close to 0, similar to the data group Dp shown in the graph in Figure 9 above. Furthermore, in this case, it is thought that it will be possible to set a threshold value with higher judgment accuracy.

[0150] (modified version) Next, a modified magnetic disk device of the embodiment will be described using Figure 12. In the modified magnetic disk device, the method for distinguishing between the postcode and the background pattern differs from that of the embodiment described above.

[0151] More specifically, in the modified magnetic disk drive, the Discrete Fourier Transform (DFT) is used to distinguish between the postcode and the background pattern. In other words, in the modified version, the Discrete Fourier Transform is used to calculate the frequency components of specific frequencies contained in the read waveform (read data).

[0152] The Discrete Fourier Transform (DFT) is a method for converting non-periodic data into a sum of trigonometric functions. While the general Fourier Transform is used for analog data, the Discrete Fourier Transform can be used for digital data.

[0153] The Discrete Fourier Transform allows the data in question to be decomposed into different frequency components such as sine waves and cosine waves. After the Discrete Fourier Transform, for example, an arbitrary read waveform of a postcode or background pattern can be represented by the following function f(x) of the variable x.

[0154] f(x)=A1sin(f1x)+A2sin(f2x)+A3sin(f3x)

[0155] In the function f(x) above, f1, f2, f3... are the frequencies of the sine waves contained in the arbitrary lead waveform, and sin(f1x), sin(f2x), sin(f3x)... are the frequency components of the sine waves contained in the arbitrary lead waveform. Also, A1, A2, A3... are the individual magnitudes of the frequency components of the sine waves contained in the arbitrary lead waveform. If the theoretical underlying pattern is a sine wave with frequency f2, then by calculating the frequency components of the sine waves contained in the arbitrary lead waveform using the Discrete Fourier Transform, it can be seen that the magnitude of the frequency component of the theoretical underlying pattern, which is a sine wave with frequency f2 and contained in the arbitrary lead waveform, is A2.

[0156] Figure 12 is a graph showing the distribution of frequency components obtained by discrete Fourier transform from the postcode read waveform or the background pattern read waveform written to the magnetic disk according to the embodiment. That is, the graph in Figure 12 shows the distribution of theoretical background pattern frequency components contained in the postcode read waveform or the background pattern read waveform, calculated by performing a discrete Fourier transform on the postcode read waveform or the background pattern read waveform.

[0157] The horizontal axis of the graph in Figure 12 represents the magnitude of the frequency components of the theoretical background pattern contained in the lead waveform of the postcode or background pattern, that is, the values ​​corresponding to the coefficients of the individual frequency components A1, A2, A3, etc. in the function f(x) described above. The vertical axis of the graph represents the occurrence rate of the theoretical background pattern in the lead waveform of the postcode or background pattern.

[0158] Furthermore, the data group Dp' plotted on the left side of the graph is data based on postcode read waveforms, and the data group Dg' plotted on the left side of the graph is data based on postcode read waveforms.

[0159] In other words, for example, suppose that among the read waveforms obtained multiple times for a postcode, the magnitude of the frequency component of the theoretical underlying pattern contained in the postcode's read waveform is 5, and the occurrence rate of the underlying pattern is 0.067. In this case, for example, out of 1000 read waveforms of the postcode, there were 67 read waveforms in which the magnitude of the frequency component of the theoretical underlying pattern contained was 5.

[0160] Furthermore, for example, if, among the lead waveforms obtained multiple times regarding the background pattern, the magnitude of the theoretical background pattern frequency component included in the postcode lead waveform is 15, and the occurrence rate of the background pattern is 0.073, then, for example, out of 1000 lead waveforms of the background pattern, there were 73 lead waveforms in which the magnitude of the theoretical background pattern frequency component included was 15.

[0161] As shown in Figure 12, when we examine the calculation results of the frequency components based on the above, we can see that even when using the discrete Fourier transform instead of the correlation function in the above embodiment, the distributions of data group Dp' and data group Dg' remain separate and do not overlap. Therefore, for example, by obtaining the read waveform of the region to be discriminated from and calculating the frequency components, it is possible to determine whether what is written to the region to be discriminated from is a postcode or an underlying pattern.

[0162] In other words, similar to the embodiment described above, during the manufacturing of the magnetic disk device, the read waveform of the background pattern before the postcode is overwritten and the read waveform of the postcode after the overwrite are obtained in advance from the magnetic disk, the frequency components contained therein are calculated by discrete Fourier transform, and a threshold used for discriminating the target region is set based on the distribution of data groups Dp' and Dg' based on each read waveform. When reading predetermined data, the above determination is made based on the pre-set threshold.

[0163] In the example graph in Figure 12, for example, the threshold TH' can be set to 11. In this case, if the magnitude of the frequency component of the theoretical background pattern included in the read waveform of the region to be discriminated is less than 11, it can be determined that what is written to that region is a postcode. On the other hand, if the magnitude of the frequency component of the theoretical background pattern included in the read waveform of the region to be discriminated is 11 or greater, it can be determined that what is written to that region is a background pattern and not a postcode.

[0164] In the modified magnetic disk device, the degree of agreement between the read waveform of the target region and the read waveform of the background pattern is determined based on the frequency components of the background pattern included in the read waveform of the target region. In this way, even when using frequency components, the degree of agreement between these read waveforms can be determined quantitatively, thereby improving the accuracy of the determination.

[0165] Here, as shown in the embodiments described above, for example, the data pattern of the background pattern can be constructed by repeating sub-data patterns having predetermined light lengths, such as 3T, 5T, and 6T. As in the modified example described above, when determining a postcode using frequency components, it is desirable to use a background pattern in which a sub-data pattern of a single light length is repeated. This is because it is possible to narrow down the frequency components that represent the background pattern from among the multiple frequency components included in the function f(x).

[0166] Furthermore, a background pattern consisting of repeating sub-data patterns with a single light length tends to have shorter repeating units than a background pattern that combines sub-data patterns with multiple light lengths. This has the advantage of reducing errors in the data included in the background pattern.

[0167] Furthermore, when using a background pattern that combines sub-data patterns of multiple light lengths, multiple frequency components included in the function f(x) will be identified as frequency components that represent the background pattern.

[0168] On the other hand, by combining sub-data patterns of multiple light lengths to construct a background pattern, any background pattern can be selected from a wide variety of options. In this case, for example, if the postcode is determined using a correlation coefficient instead of frequency components, as in the embodiment described above, it becomes unnecessary to identify multiple frequency components representing the background pattern from within the function f(x).

[0169] In addition, the postcode determination can be performed using various methods, not limited to the embodiments and modified methods described above, and a suitable background pattern can be selected according to the adopted method.

[0170] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. [Explanation of symbols]

[0171] 1...Magnetic disk drive, 10...Magnetic disk, 12...Magnetic head, 60...Microprocessor (MPU), DA...Data area, SV (SVn, SVs)...Servo area, TR...Track.

Claims

1. A magnetic disk having multiple tracks, A magnetic head for reading and writing data to the magnetic disk, Each of the aforementioned plurality of tracks is provided with a plurality of servo regions, each including at least a portion of a first physical pattern which is a physical pattern after writing a first data pattern containing positional information for each of the plurality of tracks, The system comprises a control unit for controlling the magnetic head, The aforementioned plurality of servo regions are A first servo region including the first physical pattern, Each of the plurality of tracks includes either a second servo region, which includes a second physical pattern, which is the physical pattern after writing of a second data pattern different from the first data pattern, or The control unit, The system determines whether the third servo region among the multiple servo regions of the multiple tracks has the first or second physical pattern. Magnetic disk drive.

2. The first data pattern and the second data pattern are each composed of multiple sub-data patterns. Each of the aforementioned sub-data patterns has a pattern length that is an integer multiple of the pattern length expressed as the reciprocal of a predetermined frequency. Of the aforementioned plurality of sub-data patterns, the sub-data patterns of the second data pattern are different from the sub-data patterns of the first data pattern. The magnetic disk device according to claim 1.

3. The aforementioned subdata pattern is, A data pattern in which data with the same value, either "0" or "1", The second data pattern described above is: A first sub-data pattern having a first pattern length different from any of the sub-data patterns of the first data pattern, and consisting of consecutive "0"s, A repeating pattern of a second sub-data pattern consisting of consecutive "1"s with a second pattern length different from any of the sub-data patterns of the first data pattern, The magnetic disk device according to claim 2.

4. The first pattern length and the second pattern length are equal. The magnetic disk device according to claim 3.

5. The control unit, The determination is made based on the degree of agreement between the third data pattern obtained by reading the third physical pattern written to the third servo region and the second data pattern. The magnetic disk device according to claim 1.

6. The control unit, The degree of agreement is evaluated based on the first correlation coefficient between the third data pattern and the second data pattern. The magnetic disk device according to claim 5.

7. The control unit, If the first correlation coefficient is less than a first threshold predetermined based on the second correlation coefficient between the first data pattern and the second data pattern, it is determined that the third servo region has the first physical pattern. If the first correlation coefficient is greater than or equal to the first threshold, it is determined that the third servo region has the second physical pattern. The magnetic disk device according to claim 6.

8. The control unit, The frequency components of the second data pattern included in the third data pattern are calculated by discrete Fourier transform, and the degree of agreement is evaluated. The magnetic disk device according to claim 5.

9. The control unit, If the magnitude of the frequency component included in the third data pattern is less than a second threshold preset based on the magnitude of the frequency component of the second data pattern included in the first data pattern, then it is determined that the third servo region has the first physical pattern. If the magnitude of the frequency component included in the third data pattern is greater than or equal to the second threshold, it is determined that the third servo region has the second physical pattern. The magnetic disk device according to claim 8.

10. The location information for each of the aforementioned multiple tracks is, It includes correction information for correcting the position of the magnetic head, The control unit, If it is determined that the third servo region has the first physical pattern, the position of the magnetic head is corrected based on the correction information contained in the third data pattern obtained by reading the third physical pattern written to the third servo region. The magnetic disk device according to claim 1.

11. A second data pattern, different from the first data pattern, is written to each of the multiple tracks of a magnetic disk, which are provided on each of the multiple tracks and are used when writing a first data pattern containing position information for each of the multiple tracks, thereby resulting in a plurality of servo regions having a first physical pattern which is the physical pattern after the first data pattern has been written. The first data pattern is overwritten to at least a portion of the plurality of servo regions, which include a second physical pattern that is the physical pattern after the second data pattern has been written. A first read waveform obtained by reading the first physical pattern overwritten with the second physical pattern, and a second read waveform obtained by reading the second physical pattern are obtained. Based on the first and second read waveforms, a threshold is set to determine whether a predetermined servo region among the plurality of servo regions having the plurality of tracks has the first or second physical pattern. A method for manufacturing a magnetic disk drive.

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