JP2005141874A - Magnetic disk unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve performance of a whole device by setting optimum read-write offset quantity under use environment in accordance with variation of environment temperature at the time of use in a magnetic disk device using a head utilizing magneto-resistance effect. <P>SOLUTION: This device has a temperature detecting means 13 detecting temperature variation of the magnetic disk device, read-write offset quantity is measured by an offset measuring means in accordance with variation of detection temperature of the temperature detecting means 13, and read-write offset quantity between a read head used for compensation and the write-head is changed depending on the offset value. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a magnetic disk device (international patent classification G11B 21/10) that records and reproduces data on a magnetic disk using a head using the magnetoresistive effect, and improves the control method of the magnetoresistive head. By doing so, the performance of the entire apparatus is improved.

  In recent years, various elemental technologies have been enhanced in most magnetic disk devices (HDD: hard disk drives) in response to the demand for recording density that increases year by year. Elements that determine the recording density of the HDD include a magnetic head, a recording medium, a recording / reproducing channel, and a positioning mechanism. In order to continue further improvements in recording density in line with current trends, it is important not only to improve individual elemental technologies, but also to combine each elemental technology as a system and study the total effect. Seem. Specifically, in order to achieve ultra-high density, it is necessary to dramatically improve the recording density in both the linear recording density direction (BPI) and the radial direction (TPI) of the disk.

  Regarding the magnetic head technology, the read head and the write head are separated and mounted on the same slider. A GMR (giant magnetoresistive) head is used as the read head, and an inductive head is used as the write head. The adoption of the GMR head has succeeded in enhancing the reproduction capability of the magnetic recording signal, and has largely contributed to increasing the density in the linear recording direction of the disk. For magnetic media that records data read by this GMR head, technologies such as low noise and high coercive force have been improved, and in HDI (head disk interface) and mechanical servo systems, low head flying height and head positioning technology have been enhanced. It has greatly contributed to improving the recording density in the radial direction of the disc.

  FIG. 11A is a perspective view showing a magnetic head floating concept of a hard disk drive. A slider 110 mounting the head is held in a state of floating above the magnetic disk 112 by a suspension 111 of a head actuator. Yes. A magnetic head 113 is mounted on the tip of the slider 110 as shown in FIG. As shown in FIG. 2C, the magnetic head 113 has a structure in which the write gap 114 of the write head and the read gap 115 of the read head are separated from each other, and are arranged at physically different positions.

  As the structure of the hard disk drive, as shown in the schematic plan view of the mechanism around the magnetic disk in FIG. 12, the head structure 120 is mounted on the magnetic disk 112 while rotating around the rotating shaft 121a of the actuator 121 as a fulcrum. To access. In FIG. 12, a is the distance from the rotation axis 121a of the actuator 121 to the center of the magnetic disk, L is the distance from the rotation axis 121a of the actuator to the head gap, and r is the data accessed from the center of the magnetic disk. The distance to the track. A tangential direction s of the data track on the magnetic disk 112, a so-called head gap 122 formed by a portion of the head structure 120 having a write head for recording a signal and a read head 114 for sensing and reading a reproduction signal. A skew angle 123 (θ) occurs between the straight line t connecting the centers of the actuators 121. The skew angle 123 has a unique value depending on the data track accessed by the head structure 120. The optical offset amount is generated by the optical offset amount and the skew angle 123 or the like. When the head gap 122 is located on the inner circumference side and the outer circumference side of the magnetic disk 112, the write head and the read head are physically different positions with respect to the radial direction of the magnetic disk 112 with respect to the same track position. It becomes a relationship. That is, the physical position where the write head becomes the track center and the physical position where the read head becomes the track center are different. For this reason, in order to improve the characteristics of the read / write, one is to attach the read head and the write head in the slider with high accuracy. However, in an actual head, a read / write offset amount is generated between the read head and the write head. Therefore, for a model having a plurality of heads, an optimum read / write offset amount is set for each head.

  Therefore, a method of correcting the read / write offset amount of the head structure unit 120 in the TPI direction that is currently proposed will be briefly described with reference to FIG.

  First, the read / write offset amount of the head structure 120 at an arbitrary point in each zone of the magnetic disk 112 is measured. Next, the actually measured value is determined as the read / write offset amount of the head structure 120 in the entire zone. This value is stored in advance in the fixed magnetic recording device when the fixed magnetic recording device is manufactured and shipped, and this value is used when the fixed magnetic recording device is actually used. In this method, the read / write offset amount actually measured in the zone including the data track is applied to the offset amount for a certain data track. In addition to the above methods, there is also a proposal regarding a method of performing linear interpolation for data tracks other than measurement points.

  In FIG. 13, the solid line indicates the offset amount employed by the above method, and the broken line indicates the offset amount subjected to the linear interpolation. Note that the description of the method of linear interpolation is omitted here.

As a conventional method for measuring the read / write offset amount itself, there is a method of analyzing MSE (Mean Square Error) using a read channel. (For example, see Patent Document 1)
However, the response to the temperature change of the data storage device has not been realized. As a means for detecting the temperature, a method of using as a read head temperature monitoring means has been proposed. (For example, see Patent Document 2)
JP 11-353828 A JP 2000-235701 A

  When the ambient temperature of the magnetic head or the magnetic disk changes, the coercive force of the magnetic disk changes. FIG. 14 shows an example of the temperature dependence of the magnetic disk coercivity. In FIG. 14, the horizontal axis represents the temperature change and the vertical axis represents the coercivity (Hc) of the magnetic layer of the magnetic disk. It can be seen that the lower the temperature, the greater the coercivity. It tends to get smaller. In this example, there is a change of about 20 Oe per temperature. Generally, an increase in coercive force makes it difficult to write data on a magnetic disk, and therefore, the magnetic track width tends to decrease at a low temperature and increase at a high temperature. Further, the change in magnetic track width does not change linearly. Therefore, not only the magnetic track width but also the read / write offset amount changes with temperature. At present, the read / write offset amount measured at one temperature at the time of factory shipment is used as it is even if the temperature changes when the user uses it. For example, when the read / write offset amount is measured at a temperature of 60 ° C. at the time of shipment from the factory, the read / write offset value at 60 ° C. is adopted even if the user uses the device in an environment of 5 ° C. In particular, hard disk devices for mobile use have a wider temperature range for users than those used for conventional PC use. Therefore, it is not preferable to always use a value set at a certain temperature. Further, in a situation where the recording density increases year by year and the track width has become 0.2 μm or less, if the read / write offset amount is not appropriate, the possibility of an error in data reading becomes higher than before, which is also not preferable. . In other words, the conventional method has been a problem because the optimum performance of the magnetic disk drive device cannot be obtained.

  Therefore, the present invention has been made in view of such problems, and the object of the present invention is to make it possible to adjust the offset amount of the head structure portion so as to be always more optimal, so that the GMR head can be adjusted. This makes it possible to increase the reproduction efficiency, reduce the seek time, and reduce the error occurrence rate at the time of data reading.

  The magnetic disk apparatus of the present invention is provided with temperature detecting means for detecting a temperature change of the magnetic disk apparatus, and a read head and a write head used for correction based on the detected temperature of the temperature detecting means. The read / write offset amount is changed, and the best error rate can be derived in the environment used by each user, and the reliability of the product itself can be improved.

  As described above, according to the present invention, according to the magnetic disk device of the present invention, it is possible to improve the reproduction efficiency from the GMR head by making the offset amount of the head structure portion always adjustable. In addition, the seek time can be suppressed and the error occurrence rate at the time of data reading can be reduced.

  According to the first aspect of the present invention, a magnetoresistive head in which a read head and a write head are separated is used, data is recorded on a magnetic disk by the write head, and the magnetic disk is recorded by the read head. In the magnetic disk device that reads data from the disk, the magnetic disk device has temperature detection means for detecting a temperature change of the magnetic disk device, and based on the detected temperature of the temperature detection means, between the read head and the write head used for correction This is a magnetic disk drive characterized by changing the read / write offset amount of the disk, and with this configuration, the optimum read / write offset amount in the operating environment can be obtained even if the temperature used by the user changes compared to conventional devices. It becomes possible to set.

  The invention according to claim 2 of the present invention is characterized in that the read / write offset amount changed based on the detected temperature is stored and held in advance in the magnetic disk device as data corresponding to the detected temperature. The magnetic disk apparatus according to claim 1, wherein the configuration allows an optimum read / write offset amount to be quickly set in a use environment even if the temperature used by a user changes compared to a conventional apparatus. It becomes.

  According to a third aspect of the present invention, there is provided an offset amount measuring means for measuring a read / write offset amount, and when the detected temperature is within a plurality of predetermined temperature ranges from the temperature detecting means. 2. The magnetic disk apparatus according to claim 1, wherein the read / write offset amount is measured by the offset amount measuring means, and the measured read / write offset amount is used. Even if the value changes, it becomes possible to set the optimum read / write offset amount in the use environment promptly.

  According to a fourth aspect of the present invention, the read / write offset amount for each temperature region measured by the offset amount measuring means is stored and held as data, and then the temperature detecting means 4. The magnetic disk apparatus according to claim 3, wherein the stored and held read / write offset amounts are used respectively for indicating the temperature in the temperature range of each of the temperatures measured by the offset amount measuring means. Since the read / write offset amount for each region is stored and held as data, the next time the temperature detection means indicates the temperature of those temperature regions, the read / write offset amount stored and held is respectively set. Since it is used, it is possible to set the optimum read / write offset amount in the use environment more quickly.

  The invention according to claim 5 of the present invention is the magnetic disk apparatus according to claim 1, wherein the temperature detecting means is the read head, and a detecting element is newly arranged as the temperature detecting means. It is not necessary and cannot detect temperature in real time.

  According to a sixth aspect of the present invention, in the magnetic disk apparatus according to the third aspect, the measurement of the read / write offset amount of the offset amount measuring means is executed when the magnetic disk apparatus is idle. The read / write offset amount can be measured by the offset amount measuring operation so as not to affect when the user uses it.

  According to a seventh aspect of the present invention, there is provided means for calculating a geometric read / write offset amount calculated based on the relative position of the magnetic head with respect to the magnetic disk. 4. The magnetic disk apparatus according to claim 3, wherein the read / write offset amount is measured by the offset amount measuring means using the read / write offset amount, before measuring the effective read / write offset amount. In addition, it is possible to estimate in advance where the value exists, so that quicker measurement is possible.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
FIG. 1 is a block diagram showing the configuration of the magnetic disk device according to the first embodiment of the present invention. 10 is a magnetic disk, 11 is a magnetic head, 12 is an amplifier, 13 is a temperature detecting means, 14 is an AD converter, Reference numeral 15 denotes temperature calculation means, 17 denotes optimization determination means, 18 denotes offset measurement means, and 16 denotes data storage means.

  The magnetic disk 10 records magnetic signals such as user information and servo information. The magnetic head 11 includes a read head and a write head, and reads / writes data from / to the magnetic disk 10. The amplifier 12 amplifies the signal from the magnetic head 11. The temperature detecting means 13 is disposed in the vicinity of the magnetic disk 10 and detects the temperature. When the temperature changes, the analog value output from the temperature detection means changes. As the temperature detection means 13, specifically, a read head in the magnetic head 11 or a temperature sensor may be provided.

  FIG. 2 shows a change in the analog value of the resistance value with respect to the temperature of the read head when, for example, a read head is used as the temperature detecting means 13. When the temperature changes, the resistance value of the head changes in an analog manner accordingly. The temperature is monitored when, for example, the head passes through a location on the magnetic disk 10 other than the servo or data area where the head is not read / written, or by a head that is not used in an apparatus having a plurality of heads. Can be done in real time. The AD conversion means 14 converts the resistance value accompanying the temperature change of the read head into a digital value. The temperature calculation means 15 analyzes the digital value of the read head resistance value sent from the AD conversion means and calculates the current temperature. If the correlation of the temperature dependence of the resistance value as shown in FIG. 2 is grasped in advance for all magnetic heads at the time of shipment from the factory, the temperature can be calculated based on the resistance value. Further, even when a temperature sensor is employed as the temperature detecting means 13, the temperature can be grasped similarly.

  In the data storage means 16, a table for converting the resistance value created at the time of factory shipment into a temperature as shown in FIG. 2 or a unique read for each radius of each head measured at the time of factory shipment as shown in FIG. Each table of write offset amount is stored. The optimization determination means 17 determines whether the temperature calculated by the temperature calculation means 15 is appropriate for the currently set read / write offset amount. For example, assume that the temperature at which the read / write offset amount is measured at the time of factory shipment is 25 degrees. Judgment whether or not to re-measure the optimum read / write offset amount is based on the following correspondence table. This table is also stored in the data storage means 16.

Detection temperature by temperature calculation means Read / write offset amount need to be remeasured 0 ° C to 10 ° C Remeasurement 10 ° C to 20 ° C Remeasurement 20 ° C to 30 ° C Use factory default value 30 ° C to 40 ° C Remeasurement 40 ° C ~ 50 ℃ Re-measurement 50 ~ 60 ℃ Re-measurement In this example, the temperature range is set at 10 ℃, but it can be changed depending on the model and individual magnetic head depending on the product design specifications and read head characteristics at the development stage. You can do it. When the temperature detected by the temperature calculating means 15 is 35 degrees, it is determined that remeasurement is necessary according to the correspondence table. The offset measuring unit 18 measures the read / write offset amount when the optimization determining unit 17 determines that remeasurement is necessary. For example, if the user writes data or idles when data is not read, there is no problem in use.

  FIG. 3 shows an example of a read / write offset measurement algorithm. First, a VCM (voice coil motor) is driven to seek roughly to the position where the magnetic head is measured (step S02). Then, the area around the area to be measured is DC erased and initialized so that the already written signal does not affect the current measurement (step S03). It is sufficient to erase an area about five times the mechanical track width of the normal write head. For example, if the head track width is 0.3 μm, 0.3 × 5 = 1.5 μm DC erase may be performed. Next, a minute seek (micro seek) is performed at a place to be measured (step S04). Then, the measurement data is written at the position where the current on-track is performed (step S05).

  Normally, writing is performed using a lower frequency (LF) among data frequencies actually used at the radial position. There are cases where there are six 0's between 1 and 1, such as 10000001, and there are three cases such as 10001, depending on the data to be recorded even at the same radius. As the frequency of the test, LF having a wide interval between 1 and 1 (a lot of 0 between 1) is adopted. Further, this writing range does not necessarily have to be the entire track circumference. For example, it is set to measure 20 periods of LF from the index. Then, a micro seek is performed on the inner circumference with the position thus written as a center reference (step S06). This value is determined such that if the mechanical track width is 0.5 μm, for example, the micro seek is performed on the inner periphery side of 1.0 μm. In this example, the seek is first performed on the inner circumference side, but the seek may be performed from the outer circumference side. Subsequently, the TAA (Track Average Amplitude) of the test signal written in advance by LF at the center position at the micro seek position is measured (step S07). This data is stored in a memory such as a buffer. Next, microstep is performed on the outer peripheral side (step S08).

  Since the microstep amount is a resolution when measuring the effective track width, the smaller the microstep amount, the higher the measurement accuracy. However, the smaller the value is, the more time is required for measurement, so it is necessary to set an appropriate value. For example, if the mechanical track width is 0.5 μm, it is sufficient that the microstep is about 0.05 μm. It is determined whether or not the initially set micro seek has reached the limit (step S09).

  If the micro seek has not reached the limit, steps S07 and S08 are repeated again. This data is also stored in a memory such as a buffer. When the micro seek limit is reached, the read / write offset amount is calculated in step S10. The read / write offset amount is the micro seek amount when the TAA value is the largest when the position where data is written is the origin. This completes the series of read / write offset measurement operations.

  FIG. 4 shows an example of TAA measurement results at a certain temperature. Although there are three graphs, the results are for the disc ID (inner circumference), MD1 (middle circumference), and OD (outer circumference). The horizontal axis of the graph is the microstep amount, and the vertical axis is the TAA value measured at each position. The individual heads have different TAA characteristics when the position in the TPI direction is changed. Of course, the read / write offset amount differs for each magnetic head.

  For example, the read / write offset amount when the temperature is 5 ° C., 25 ° C., and 45 ° C. at the same location on the magnetic disk is as shown in FIG. In FIG. 1, when the optimization determination unit 17 determines that remeasurement is necessary based on the temperature indicated by the temperature calculation unit 15, the read / write offset amount is remeasured at a certain point (for example, ID) on the magnetic disk. The result is updated in the offset table. Regarding MD and OD, it is also possible to estimate the temperature dependence of the offset amount without actually measuring it by analyzing the change in the read / write offset amount with respect to the temperature at the ID. Thereby, the time for re-measurement of the offset amount in the idle state can be shortened. Then, this value is used until a temperature change exceeding a specified value is detected and the optimization determination means 17 determines again that remeasurement is necessary. By using such a method, the optimum read / write offset amount can be set in real time according to the temperature environment currently used.

(Embodiment 2)
In the magnetic disk device according to the second embodiment of the present invention, the read / write offset amount between the read head and the write head is measured in advance at a plurality of temperatures, and the read / write offset amount is measured at the plurality of temperatures. Data is stored, and a correlation table is generated to generate a correlation table of the read / write offset amount with respect to the temperature by referring to the corresponding read / write offset amounts when measured at a plurality of temperatures. FIG. 6 is a flowchart showing the flow.

In FIG. 6, first, information related to the temperature around the magnetic head and the magnetic disk is detected (step S13). For example, when a head is used as the detecting means, analog data of the resistance value of the read head is used. Next, the information related to the analog temperature obtained in step 13 is converted into digital data (step S14). Then, the current temperature is calculated based on the digitized information (step S15). For example, the current temperature is calculated based on the correlation between the head resistance value and the temperature as shown in FIG. Then, a track profile as shown in FIG. 4 is created under the current temperature environment, and a read / write offset amount is created at several points on the magnetic disk (step S16). In step 16, the read / write offset amount measured at several points on the magnetic disk is stored for each head. The temperature condition data measured at this time is also recorded at the same time. The following table is an example of data to be stored.

Read / write offset (um) Temperature (℃)
Magnetic disk radius Head 1 Head 2
ID 0.167 0.129 25
MD1 -0.353 -0.393 25
MD2 -0.693 -0.733 25
OD -0.972 -1.013 25
Next, the temperature around the magnetic disk device is changed using a thermostatic chamber (chamber) or the like. The temperature is changed to 45 ° C., for example, and the setting is confirmed in step S18. Returning to step S13 again, the temperature is confirmed by the magnetic disk device itself, and the same steps are performed. An offset correspondence table corresponding to each head is created and stored even at 45 ° C. Thus, since the read / write offset amount at each temperature is obtained as shown in FIG. 5, an offset correlation table can be created (step S19). FIG. 7 shows an example of the offset correlation table with the magnetic disk ID created in step S19. From this table, the read / write offset amount at the current temperature is obtained for each head. Such data is similarly recorded at points such as the magnetic disk MD and OD.

  If the above-described series of steps are performed at the time of shipment from the factory, the data storage device itself can have the temperature dependence of the read / write offset amount before going to the user. That is, it is no longer necessary to re-measure the offset when the temperature changes after reaching the user's hand.

(Embodiment 3)
In the magnetic disk device according to the third embodiment of the present invention, the measured temperature of the magnetic disk device changes from one operating temperature range to another operating temperature range by using the correlation table corresponding to the temperature. FIG. 8 is a data storage method having a step of loading a different one of the correlation tables every time and a step of performing a next read by using the updated table. .

  At the time of factory shipment, for example, a read / write offset amount at 25 ° C. is set and shipped (step S22). Thereafter, when the user is using it, that is, when the data storage device is powered on, the temperature is always monitored as in the first embodiment (step S23). After grasping the current temperature in step 23, the offset correlation table created at the time of factory shipment by the method shown in the embodiment 2 is referred to (step S24). Then, the optimum offset amount at the current temperature is checked from the correlation table, and the value is set to be used for reading data in the actual data storage device (step S25). By performing the operations from S21 to S26 in real time, the optimum read / write offset amount at the current temperature can always be set in each magnetic head.

(Embodiment 4)
In the magnetic disk apparatus according to the fourth embodiment of the present invention, the step of calculating the geometric read / write offset amount calculated based on the relative position of the magnetic head with respect to the magnetic disk is performed before the read / write offset amount is measured. FIG. 9 shows the flow of the flow.

First, the geometric offset amount of the disk is calculated (step S22). The skew angle θ in FIG. 12 can be calculated if the distance r from the magnetic disk center to the accessed data track, the distance L from the actuator to the head gap, and the distance a from the actuator to the magnetic disk center are known. Is possible. That is, the following calculation formula θ = π / 2-acos {(L2 + r2-a2) / (2 × Lxr)}
Is calculated arithmetically. When the skew angle θ is obtained, the read / write offset amount obtained geometrically based on the dimensional specifications of the head shown in FIG. 11 can be calculated. That is, the following calculation formula.

(R-W distance) xsinθ
In this way, seek is first performed with the calculated theoretical offset amount (step S23). Thereafter, TAA1 is measured (step S24). After measuring TAA1, seek to the outer peripheral side with respect to the position where TAA1 is measured (step S25). The seek amount is preferably about 20% of the track pitch. TAA2 is measured at this position (step S26). Next, after measuring TAA2, seek to the inner circumference side with respect to the position where TAA1 is measured (step S27). The amount of seek on the inner peripheral side is also about 20% of the track pitch. TAA3 is measured at this position (step S28). When TAA1, TAA2, and TAA3 are obtained, the three values are compared. Case2 is on the outer peripheral side from the peak. Case3 is in the vicinity of the peak. First, it is determined whether or not the case 1 corresponds to TAA1 <TAA2, TAA1> TAA3 (step S29). If applicable, it means that it is on the inner peripheral side from the peak, so seek to the outer peripheral side and go to step S24 again. If it does not correspond in step S29, then it is determined whether case 2 corresponds to TAA1> TAA2 and TAA1 <TAA3 (step S30). If applicable, it means that it is on the outer peripheral side from the peak, so seek to the inner peripheral side and proceed to step S24 again. If it does not correspond in step S30, then it is determined as case 3 whether TAA1> TAA2 and TAA1> TAA3 are satisfied (step S31). If it corresponds, it is in the vicinity of the peak, so the process is terminated (step S32). FIG. 10 schematically shows the positional relationship in the track profile in the three cases of case1, case2, and case3. Case 1 is on the inner peripheral side from the peak indicating the read / write off-track amount. In this way, the read / write off-track amount obtained from the actual measurement of the track profile is obtained, and an eye is placed near the peak to improve the measurement time, and the periphery of the peak can be focused on. .

1 is a block diagram showing a configuration of a magnetic disk device according to a first embodiment of the present invention. The temperature dependence of the resistance value of the read head of the magnetic disk device A flowchart showing a flow of processing for creating a track profile of the magnetic disk device The figure which shows the off track quantity of the same magnetic disk unit Diagram showing the temperature dependence of the track profile of the magnetic disk device Flowchart of the process flow of the magnetic disk device according to the second embodiment of the present invention. The temperature dependence of the off-track amount of the magnetic disk device Flowchart of processing flow of the magnetic disk device according to the third embodiment of the present invention. Flowchart of the process flow of the magnetic disk device according to the fourth embodiment of the present invention. The figure which shows the detection process of the track profile peak of the magnetic disk device A perspective view and a partially enlarged plan view showing a general magnetic disk device head flying concept Top view of a typical magnetic disk unit The figure which shows the amount of offset in a general magnetic disk unit Diagram showing temperature dependence of coercivity of magnetic disk

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Magnetic disk 11 Magnetic head 12 Amplifier 13 Temperature detection means 14 AD conversion means 15 Temperature calculation means 16 Data storage means 17 Optimization determination means 18 Offset measurement means 110 Slider 111 Suspension 112 Magnetic disk 113 Magnetic head 114 Write gap 115 Read gap 120 Head structure 121 Actuator 122 Head gap 123 Skew angle

Claims (7)

In a magnetic disk device, which uses a magnetoresistive head in which a read head and a write head are separated, records data on the magnetic disk by the write head, and reads data from the magnetic disk by the read head, the magnetic disk It has a temperature detection means for detecting a temperature change of the apparatus, and the read / write offset amount between the read head and the write head used for correction is changed based on the detected temperature of the temperature detection means, Magnetic disk unit to be used. 2. The magnetic disk apparatus according to claim 1, wherein the read / write offset amount changed based on the detected temperature is stored and held in advance in the magnetic disk apparatus as data corresponding to the detected temperature. An offset amount measuring means for measuring the read / write offset amount is provided, and when the detected temperature falls within a plurality of predetermined temperature ranges from the temperature detecting means, a read / write offset is set by the offset amount measuring means. 2. The magnetic disk apparatus according to claim 1, wherein the quantity is measured and the measured read / write offset quantity is used. The read / write offset amount for each temperature region measured by the offset amount measuring means is stored and held as data, and then when the temperature detecting means indicates the temperature of those temperature regions, 4. The magnetic disk apparatus according to claim 3, wherein the read / write offset amount stored and held is used. 2. The magnetic disk apparatus according to claim 1, wherein the temperature detecting means is the read head. 4. The magnetic disk device according to claim 3, wherein the measurement of the read / write offset amount by the offset amount measuring means is performed when the magnetic disk device is idle. Means for calculating a geometric read / write offset amount calculated based on the relative position of the magnetic head to the magnetic disk, and using the calculated geometric read / write offset amount, the offset amount 4. The magnetic disk apparatus according to claim 3, wherein the read / write offset is measured by the measuring means.

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