Magnetic disk device using non-aligned read and write heads with tracking servos and a rotary actuator

A magnetic head drive including a composite magnetic head structured by integrally combining a write head into a record head and a magnetic disk having a servo area where position information of the composite magnetic head is recorded and a data area where data is recorded. The servo area includes a positioning data area having head positioning information, and the head has an erased area generated by recording an AC signal having a frequency higher than a burst pattern in an area other than the burst pattern including information of positioning the composite magnetic head of said positioning data area.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a disk drive, such as a hard disk drive 
and a floppy disk drive, using mainly a composite magnetic head with a 
thin film type wherein a write head and a read head are structured in a 
composite form. 
2. Description of the Related Art 
In the conventional magnetic disk drive, there is a disadvantage in which 
the performance of the recording and that of the reproducing cannot be 
suitably designed since recording and reproducing of signals are performed 
by the same head even if an access system of the head differs. As a 
technique for solving this problem, there is known a method for making the 
recording and the reproducing suitable independently by structuring the 
write head and the read head in a composite form. This type of the head is 
called as a composite head to distinguish it from the conventional 
recording/reproducing common head. 
A head in which a magnetic force generating coil is combined into a 
ring-shaped core, which is designed such that a suitable signal recording 
can be performed as a recording head, is used (hereinafter called an 
inductive head for convenience based on a reproducing principle though it 
is not suitable for a name of the write head). Also, an inductive head or 
a magnetoresistive head (hereinafter called an MR head, and there is a 
case in which an MR head of composite type is simply called an MR head) is 
used as a read head. Then, these heads are structured in a composite form 
(a case of the layer structure as in the thin film type is included), 
thereby the composite head is structured. 
In consideration of the miniaturization of the future magnetic disk drive 
and inclination of high density thereof, it is desirable that there is 
used a composite head wherein there is provided such a head which is 
superior to the conventional inductive head in sensitivity of reproducing. 
The MR head whose reproducing output has no relation with the relative 
speed of the head and the disk is used as a read head, and the read head 
and the write head of the inductive type are structured in a composite 
form. 
In a small-sized disk drive, a rotary actuator is used since the structure 
is simpler than a linear actuator and there are advantages in terms of low 
cost, excellent vibration resistance, low consumption of electric power, 
and so on (FIGS. 1A and 1B show one example of a magnetic disk drive of 
rotary actuator system). 
The following explains a case in which the magnetic disk drive of the 
rotary actuator system using the composite head in which the write head 
and the read head are structured in a composite form (for example, a thin 
film magnetic head of composite type, which is structured by layering a 
thin film magnetic head of inductive type, serving as a write head, and MR 
head, serving as a read head). As shown in FIGS. 1A to 2, if the composite 
magnetic head is accessed in the range from an innermost track position to 
an outermost track by rotating an arm of the rotary actuator, 
misregistration is generated at a position of a recording track on the 
magnetic disk and a position of the read head by a skew angle .theta.. As 
shown in FIG. 2, an amount of track misregistration can be described by 
D.multidot.sine.theta.. D shows a space between a magnetic gap of the 
write head and that of the read head (FIG. 2 shows a case using the 
inductive head at both write and read operations, and central position of 
a reproducing element effect section is meant in the case of the MR head 
of FIGS. 1A and 1B, but hereinafter is simply called a magnetic gap 
because of the similar meaning). 
In the specification of the present invention, in order to easily 
understand the relationship between the head position and the magnetic 
disk rotating direction, the relationship is shown in FIG. 2. An area 
where the write head traces is called a recording track, and an area where 
the read traces is called a reproducing track. In contrast, an area on the 
magnetic disk which the recording/reproducing is originally performed is 
called a data track or simply a track. In a case in which the magnetic 
disk drive is structured so that the recording track and the reproducing 
track are conformed to each other when the positioning is performed at the 
central track (in a case in which the width of the recording track and the 
width of the reproducing track are different, the centers of both 
recording and reproducing tracks are conformed to each other, and in a 
case in which the centers of both tracks deviate, an amount of 
misregistration is shown by a distance between both centers), the 
positional relationship between the recording and reproducing tracks at 
each track position, when the head is moved from the outermost 
circumference to the innermost circumference, and an inclination of the 
recording/reproducing gap are shown in FIGS. 3A to 3C. FIGS. 3A to 3C show 
the inclination of the recording/reproducing gap, and the gap therebetween 
is described wider than the actual case. 
FIG. 4 shows an example of a format of the magnetic disk drive. At a 
beginning of each sector, there is provided an ID section where ID 
information of the sector (cylinder number, head number, presence or 
non-presence of defect depending, etc.) is recorded. It is required that 
ID information be read before processing of a data area in both cases, 
that is, a case in which data is reproduced and a case in which data is 
recorded. 
A mode is changed so that the write head is on a data track at a write 
operation and the read head is on a data track at the write operation. In 
this case, if an offset amount of a voice coil motor (VCM) is finely 
adjusted so that a desired head follows the data track, the data section 
can be recorded/reproduced without deteriorating S/N. However, since the 
ID section is required to be read at both read and write operations, the 
following problem occurs. When using the reproducing head, it is extremely 
difficult to change the mode such that the write head is set to be on 
track after reproducing the ID section which physically exists in the same 
sector as the reproducing head since the mode change must be 
instantaneously performed. 
If the width of the recording head is made sufficiently wider than the 
width of the read head, the reproducing track can be included in the 
recording track. Due to this, ID information can be read without having 
deterioration of the quality of a signal of the data section caused by 
writing/reading head misregistration. However, this is not favorable in 
view of the point that a track density is increased. 
"Track Density Constraints in the Application of MR Head Technology" IEEE 
TRANSACTION ON MAGNETICS, Vol. 28, No. 5, P. 2728, 1992 discloses the 
following two methods: 
(1) The ID area and the data area are provided in a different physical 
sector; and 
(2) A plurality of ID areas (for reproducing and recording) are provided. 
However, in the method (1), a throughput of data access is lowered. In the 
method (2), though there is no description of the specific structure, it 
is described that the ID area is divided into odd tracks and even tracks, 
and a plurality of ID areas are provided. 
FIG. 5 is a view showing an example having a plurality of ID areas. FIG. 6 
is a view showing a method for recording a servo signal. According to FIG. 
6, for example, servo information is written as shown by 1 to the end in 
accordance with head positions 1 to 5 at a servo write operation. Then, 
for example, the write head and the read head are positioned at a center 
of the track at the write and read operations, respectively. According to 
FIG. 5, there is provided the structure in which each ID area of each 
track of the odd and even tracks is wider than the track, whereby ID 
information is correctly read. This structure is an effective method to 
solve the track misregistration. However, according to this method, since 
the servo write does not conform to the ID area of each track (that is, 
information is overwritten with a half pitch of the read head), it is 
required that ID information be written twice, and it takes much time to 
write ID information. 
FIG. 7 is a view showing a general structure of the servo area. 
Generally, the servo area has an address AGC area, an erased area, a track 
address code area, a burst AGC area, a positioning data area, and a gap 
section. The address AGC area controls a gain of an auto gain control 
(AGC) amplifier so as to standardize amplitude of a reproduced signal, and 
ensures the detection of the sequential erased area and the reproduction 
of the track address code area. The erased area recognizes the start of 
the servo area. An address in which the head exists is allotted to the 
track address code area. The burst AGC area adjusts the gain of the AGC 
amplifier so as to ensure extraction of positioning information from burst 
pattern data of the sequential positioning data area. The gap section 
absorbs some of the rotation jitter of the magnetic disk. 
Generally, as shown in FIG. 8, the positioning data area of the hard disk 
drive, in which the conventional inductive head is provided, has a 
plurality of burst areas (in this example, A, B, C and D areas). In each 
burst area, a burst signal area and an area erased in a DC manner are 
alternately provided in a direction of the width of the track. That is, 
the burst signal area and the erased area are provided as deviating in the 
width direction of the track. 
A dashed and dotted line of FIG. 8 shows a center of each track. In order 
to position the magnetic head at the center of the track, the magnetic 
head is controlled such that a value of (a-b)/(a+b) is set to 0 from 
amplitude a of the reproduced signal sent from the burst area A and 
amplitude L of the reproduced signal sent from the burst area B. 
The burst areas C and D are recorded at a position which differs a half 
pitch from the burst A and the burst B to obtain a good linearity even in 
a case in which the magnetic head is presented in an area where the 
magnetic head crosses the adjacent two tracks (i.e., in a case in which a 
head position has an incorrect linearity obtained from position 
information generated by the signals of the burst A and the burst B). 
In order to form the above-mentioned positioning data area, as shown in 
FIGS. 9A to 9C, the recording of the positioning data area is performed by 
feeding the magnetic head by a half of the track pitch Tp, and overwriting 
information on a base recording before the movement of the head to another 
portion, and adjusting the phases. 
When the positioning data area is recorded by using an inductive recording 
MR reproducing composite head (hereinafter, referred to as a composite MR 
head), it is known that an edge bipolar charge in a of the width of the 
track is generated at both sides of the recording track. The similar 
phenomenon is generated when a DC erase is performed as shown FIG. 10A. 
FIG. 10B shows the structure of the write head section of the composite MR 
head. The magnetic gap is formed by a lower pole on the reproducing side 
and the upper pole on the trailing side. In reproduction using the 
composite MR head, if the magnetic flux sent from the edge bipolar charge 
is received by the MR film of the MR head, there is a problem in which 
offset is generated in the reproduced signal in a DC manner. 
When using the conventional inductive head, as shown in FIG. 11A, when the 
edge bipolar charge appears in the portion overwritten by the DC erase of 
positioning data, and the edge bipolar charge is reproduced by the 
composite MR head so as to obtain head positioning information, since the 
MR head obtains the reproduced signal at the position where the MR head 
crosses the edge of the burst area, the MR head is subjected to influence 
of the edge bipolar charge. Due to this, the reproduced signal of head 
positioning information has a DC offset in every burst area shown FIG. 
11B. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a magnetic disk drive in 
which ID information can be stably read from a magnetic disk during write 
and read operations with high reliability. 
According to a first aspect of the present invention, there is provided a 
magnetic head disk drive comprising: a composite magnetic head structured 
by integrally combining a write head into a record head; and a magnetic 
disk having a servo area and a data area, wherein the servo area includes 
a positioning data area having head positioning information, wherein data 
is recorded in the data area and wherein the magnetic composite head has 
an erased area generated by recording an AC signal having a frequency 
higher than a burst pattern in an area other than the burst pattern, 
including information for positioning the composite magnetic head in the 
positioning data area. Particularly, the magnetic disk drive of the 
present invention further comprises head tracking servo means for 
providing a positioning offset to the composite magnetic head such that 
the write head is set to be on-track in the data area of the magnetic disk 
during a write operation and the read head is set to be on-track in the 
data area of the magnetic disk during a read operation. 
According to the first aspect of the present invention, when a servo 
pattern is read by an MR head, it is possible to avoid generating a DC 
offset when reading head positioning information of head positioning data, 
thereby making it possible to achieve correct positioning. 
Moreover, according to the first aspect of the present invention, the AC 
signal having a frequency higher than the burst pattern is recorded in an 
area, which is conventionally DC-erased, for position data, thereby making 
it possible to prevent the appearance of an edge bipolar charge and 
prevent the generation of a DC-offset of the read positioning information. 
In the above-mentioned structure, the magnetic disk drive of the present 
invention further comprises a rotary actuator for mounting the magnetic 
head on one end and for rotating around the other end, wherein the 
magnetic disk further includes first ID information recorded at a position 
where the read head is set to be on-track during the data read operation 
and second ID information recorded at a position where the read head is 
set to be on-track during the data write operation. 
In order that the write head is set to be on-track in the data area at the 
write operation and the read head is set to be on-track in the data area 
at the read operation, a positioning offset is provided to the magnetic 
head. Also, there are provided first and second ID information, wherein 
first ID information is recorded where the read head is set to be on-track 
during the data read operation and wherein second ID information is 
recorded where the read head is set to be on-track during the data write 
operation. Since the ID section can be reproduced when the read head is 
on-track, in either case, information of the ID section can be stably read 
at both write and read operations. 
Moreover, in the above-mentioned structure, the magnetic disk drive further 
comprises a rotary actuator for mounting the magnetic head on one end and 
for rotating around the other end, wherein the magnetic disk further 
includes an ID area having first ID information read by the read head 
during the data read operation and second ID information, recorded using a 
format different from the first ID information, read by the write head 
during at the data write operation. 
In order that the write head is set to be on-track in the data area at the 
write operation and the read head is set to be on-track in the data area 
at the read operation, a positioning offset is provided to the magnetic 
head. Also, first ID information, which is recorded by the format suitable 
for reading by the read head, is read at the data read operation when the 
read head is on-track. Also, second ID information, which is recorded in a 
format suitable for reading by the write head, is read at the data write 
operation when the write head is on-track. Thus, information of the ID 
section can be stably read at both write and read operations. 
Furthermore, in the above-mentioned structure, the magnetic disk drive of 
the present invention further comprises a rotary actuator for mounting the 
composite magnetic head on one end and for rotating around the other end, 
wherein the magnetic disk further includes an ID area recorded at a 
recording density different from the data area such that data is read by 
the read head at the data read operation and data is read by the write 
head at the data write operation. 
In order for the write head to be on-track in the data area at the write 
operation and the read head to be on-track in the data area at the read 
operation, a positioning offset is provided to the magnetic head. Also, ID 
information is recorded with relatively low record density as compared 
with the data area and can be read by any of the read and write heads. 
This ID information is read by the read head at the read operation when 
the read head is on-track and by the write head at the write operation 
when the write head is on-track. Thus, information of the ID section can 
be stably read at both write and read operations. 
According to a second aspect of the present invention, there is provided a 
magnetic disk drive comprising: a rotary actuator; a rotary actuator arm 
having a first end and a second end connected to the rotary actuator; a 
composite magnetic head, mounted on the first end of the rotary actuator 
arm, and structured by integrally combining a write head into a read head; 
a magnetic disk having a servo area where positioning information of the 
composite magnetic head is recorded and an ID area where ID information of 
a sector is recorded, the ID area including a first ID area where a 
plurality of odd track ID areas are continuously formed and a second ID 
area where a plurality of even track ID areas are continuously formed; and 
head tracking servo means for providing a positioning offset to the 
composite magnetic head such that the write head is on-track in the data 
area of the magnetic disk at a write operation and the read head is 
on-track in the data area of the magnetic disk at a read operation; 
wherein the servo tracking servo means includes means for setting a width 
of each of the odd and even track ID areas to an integral multiple of a 
pitch width for servo positioning of the composite magnetic head recorded 
in the servo area. 
According to the second aspect of the present invention, the ID area is 
divided into two areas of odd and even tracks, and the width of each of 
the ID area is set to an integral multiple of a pitch width of the servo 
positioning of the magnetic head. Due to this, since it is not needed that 
ID information be overwritten with a half pitch of the write head, time 
for recording ID information can be shortened. 
According to a third aspect of the present invention, there is provided a 
magnetic disk drive comprising: a rotary actuator; a rotary actuator arm 
having a first end and a second end connected to the rotary actuator; a 
composite magnetic head, mounted on the first end of the rotary actuator 
arm, and structured by integrally combining a write head into a read head; 
a magnetic disk having an ID area where ID information of a sector is 
recorded; and head tracking servo means for providing a positioning offset 
to the composite magnetic head such that the write head is set to be 
on-track in the data area of the magnetic disk at a write operation and 
the read head is set to be on-track in the data area of the magnetic disk 
at a read operation; wherein the ID area of the magnetic disk includes a 
first ID area and a second ID area, where the first ID area includes an 
area for recording ID information of an odd number track and an erased 
area for recording erasing information, the ID information and the erasing 
information being alternately recorded and where the second ID area 
includes an area for recording ID information of the plurality of even 
number tracks and an erased area for erasing information, the ID 
information and the erasing information being alternately recorded. 
In the above third aspect of the present invention, a positioning offset is 
provided to the magnetic head in order that the write head is set to be 
on-track in the data area at the write operation and the read head is set 
to be on-track in the data area at the read operation. Also, the record 
positions of ID information on the odd numbered tracks and even numbered 
tracks are recorded based on the relation of the phase difference between 
the odd and even numbered tracks, and both sides of the area where ID 
information is recorded is an erased area. Due to this, a noise component 
cannot be read from the adjacent tracks even if the ID section is read at 
the recording mode when the read head is on-track. Thus, information of 
the ID section can be stably read at both write and read operations. 
According to a fourth aspect of the present invention, there is provided a 
magnetic disk drive comprising: a rotary actuator; a rotary actuator arm 
having a first end and a second end connected to the rotary actuator; a 
composite magnetic head, mounted on the first end of the rotary actuator 
arm, and structured by integrally combining a write head into a read head; 
a magnetic disk having an area where cylinder number information is 
recorded, an area where sector number information is recorded, a servo 
area where servo information is recorded, and a data area where data is 
recorded; head tracking servo means for providing a positioning offset to 
the composite magnetic head such that the write head is set to be on-track 
in the data area of the magnetic disk at a write operation and the read 
head is set to be on-track in the data area of the magnetic disk at a read 
operation; and storing means for storing a defect sector of the magnetic 
disk and defect information of a defect track. At least one of the 
cylinder number information and sector number information is recorded with 
a width equal to or larger than a track pitch. The cylinder number 
information is recorded in different phase relationships in accordance 
with a remainder obtained when the cylinder number is divided by n (n:2 or 
more natural number). The magnetic disk has an area recording first 
cylinder information recorded at a position where the read head is 
on-track at the read operation, second cylinder information recorded at a 
position where the read head is on-track at the data write operation, and 
sector number information recorded at a forward portion of each data 
sector with a width at least equal to or larger than a track pitch. The 
read head reads the servo information, and the servo information includes 
first servo information recorded such that the write head is set to be 
on-track in the data area at the write operation, and second servo 
information recorded such that the read head is set to be on-track in the 
data area at the read operation. 
According to the fourth aspect of the present invention, there is provided 
head tracking servo means for positioning the magnetic head such that the 
write head is set to be on-track in the data area of the magnetic disk at 
a write operation and the read head is set to be on-track in the data area 
of the magnetic disk at a read operation. Moreover, there is provided an 
area where cylinder number information is recorded to be close to an area 
where servo information is recorded, so that the cylinder number can be 
detected and confirmed. Furthermore, there is provided an area where 
sector number information is recorded at the forward portion of each data 
sector, so that the sector number can be confirmed before recording and 
reproducing. 
Moreover, in order to store the defect sector on the disk and defect track 
information into a specific memory on the magnetic disk or a nonvolatile 
solid-state memory, the defect sector and defect track information are 
read at the time of starting the device, thereby making it possible to 
confirm beforehand whether or not the sector to be accessed is a defect 
sector without accessing it. The head number does not have to be written 
to the ID section if a physical head number and a logical head number are 
the same. In some magnetic disk drives, when the logical head number is 
seen from the outer unit, the cylinder number and the sector number are 
different from the logical head number, the cylinder number and the is 
sector number, which are recorded on the disk. This case can be dealt with 
by providing an allocation table in a suitable memory. Therefore, the head 
number can be confirmed without recording it in the ID section. In other 
words, the ID section can be omitted. 
In the above-mentioned structure of the first to fourth aspects of the 
present invention, when a magnetic disk is used in which servo information 
for positioning the head, including position error information, is 
recorded on a data surface, the following points can be provided. 
The magnetic disk alternately and dispersively records first servo 
information corresponding to the read head and second servo information 
corresponding to the write heads. The head tracking servo means includes 
means for positioning the composite magnetic disk based on position 
information obtained by synthesizing first and second position 
information. The first position information is obtained by cutting a low 
frequency component, including a DC component from first an d second 
position error information showing position errors of the read and write 
heads alternately, obtained from first and second servo information read 
from the magnetic disk by the head. The second position information is 
obtained by selecting first position error information at the read 
operation and second position error information at the recording time, 
respectively. 
Discrimination information for discriminating whether servo information is 
first servo information or second servo information is preferably included 
in first and second servo information recorded in the magnetic disk. 
If a sampling frequency is set to Fs and n is set to an integer number (0, 
1, 2, . . . ), the above first position error signal is a signal in which 
a misregistration is generated by displacement of a complementary angle in 
only the frequency of n.multidot.Fs/2, and an error is included. If n is 
an even number equal to or more than 2, since the frequency component 
passes through a Zero-order holding circuit and its output becomes a zero 
output, the frequency component does not appear. Also, regarding the 
frequency component wherein n is an odd number, since the level is reduced 
as n becomes larger due to a low pass filter characteristic of the 
Zero-order holding circuit, such a frequency component can be ignored. 
However, the frequency component is Fs/2 when n=1, and the frequency 
having such a frequency component cannot be ignored. Due to this, first 
and second position error information is cut by the band rejection filter 
of a narrow band frequency for cutting the component of Fs/2. The 
frequency of this filter is fixed, so this filter has little influence on 
other frequencies having a narrow band. In this case, n=0 shows a direct 
current component. However, since an error is included in the direct 
current component, a low frequency component including a DC component is 
cut from first and second position error information, and the obtained 
information is used as first position information. 
On the other hand, first and second position error information is 
respectively selected in accordance with the reproducing or the recording, 
so that the selected information is used as a second position signal. A 
sampling rate of the second position information is Fs/2, and the 
frequency band is a half of the band frequency of first position 
information, but the band frequency is correct, and includes no error. 
However, since the band frequency of the second position information is 
narrow, phase distortion is generated in an area where the frequency is 
high. In order to avoid the generation of phase distortion, it is 
preferable that only the low frequency portion is extracted through the 
low pass filter. 
The above obtained first position information including no DC component and 
second position information having a small amount of AC component are 
synthesized to form third position information, thereby obtaining 
substantially complete position information. The above-obtained third 
position information has no component of Fs/2. However, since third 
position information is substantially the same as position information of 
the sampling rate Fs, the phase distortion is low up to the high 
frequency. Therefore, the head tracking servo system for positioning the 
composite magnetic head is structured by using the above-obtained third 
position signal, whereby the trace of the read head is precisely conformed 
to that of the write head, so that there can be realized the magnetic disk 
drive in which the recording tracks are arranged with high density. 
In the structure of the first through fourth aspects of the present 
invention, the head tracking servo means preferably includes a band 
rejection filter for cutting a frequency component of a 1/2 sampling rate 
from first position information. Also, the head tracking servo means 
preferably includes a low pass filter for cutting a high frequency 
component of the second position information. Moreover, a Zero-order 
holding circuit for inputting position error information is preferably 
provided. 
As mentioned above, according to the pre sent invention, in the magnetic 
disk of the rotary actuator system on which the composite magnetic disk 
having the writing/reading heads in the composite form is mounted, since 
ID information by the format improved to be suitable for the composite 
head is provided, ID information can be surely re ad even if there is 
misregistration in the recording track/reproducing track. Also, ID 
information can be surely read even if the read head is in an off-track 
state to the reproducing track at not only the read operation but also the 
write operation. Therefore, the recording track density can be expected to 
be improved as compared with the prior art. 
Moreover, according to the present invention, in the magnetic disk of the 
present system, the composite writing/reading heads are mounted on the 
rotary actuator. Since cylinder number information and sector number 
information of the improved format for the composite head are provided, 
the information can be surely read even if there is misregistration in the 
recording track/reproducing track. Also, the, information can be surely 
read even if the read head is in an off-track state to the reproducing 
track at not only the read operation but also the write operation. 
Therefore, the recording track density can be expected to be improved as 
compared with the prior art, and the format efficiency of data can be 
improved. 
In addition, since a part of conditions necessary for confirming ID 
information can be written in recording servo information, there can be 
obtained an advantage in which the number of times of servo-disk 
formatting and the total sum of time can be reduced. This advantage is 
extremely helpful in realizing the high density magnetic disk drive on 
which the composite magnetic head is mounted. 
Moreover, according to the present invention, in the magnetic disk of the 
rotary actuator system on which the composite magnetic disk having the 
writing/reading heads in the composite form is mounted, the composite 
magnetic head is positioned at a different position at each of the read 
and write operations, and the read head and the write head are positioned 
at the same trace at the read and write operations. Thus, there can be 
provided the magnetic disk drive with high record density without 
narrowing an effective crack width. 
Additional objects and advantages of the present invention will be set 
forth in the description which follows, and in part will be obvious from 
the description, or may be learned by practice of the present invention. 
The objects and advantages of the present invention may be realized and 
obtained by means of the instrumentalities and combinations particularly 
pointed out in the appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Embodiments of the present invention will be explained with reference to 
the drawings. 
A magnetic disk drive of a first embodiment of the present invention will 
be explained with reference to FIGS. 12A to 13B. 
When a composite magnetic head, in which a write head and a read head are 
structured in a composite form, is applied to a magnetic disk drive of a 
rotary actuator system, if the composite head is moved from an inner 
circumference to an outer circumference by a rotation of the rotary 
actuator, each of the write head W and the read head R generates a 
positional misregistration at a respective track area as shown in FIGS. 
12A to 12C. 
In view of the design of the system, it is common to set the size of the 
track width and a guard band to a preferable relation. In this case, for 
simplifying the explanation, track pitch, the read head and the write head 
are drawn with the same width (the same in the following figures). In 
reality, as shown in FIGS. 3A to 3C, the head is inclined to a track 
direction (disk rotating direction). This is also omitted to simplify the 
explanation (the same in the following figures). 
FIGS. 12A to 12C show the positional relationship between an ID area format 
and the head in odd tracks of each of an outer circumference section, a 
center circumference section, and an inner circumference section. In order 
that the write head is set to be on-track in the data area of the magnetic 
disk at a write operation and the read head is set to be on-track in the 
data area of the magnetic disk at a read operation, a positioning offset 
is provided to the magnetic head, thereby making it possible to perform 
read/write operations in the data area. In this case, the read head reads 
information of an ID section in an off-track state at the recording mode. 
According to the present invention, since both sides of the ID section are 
an erased area, and there is no case in which a noise component is read 
from the adjacent tracks. Therefore, according to the present invention, 
information of the ID section can be stably read at both write and read 
operations. In the present invention, since both sides of the ID section 
are erased, deterioration of quality of the signal of ID information is 
lenient in a case that the head is off-track by various types of noise and 
disturbance. Due to this, the present invention has an advantage in which 
an off-track margin is larger than a conventional method in which data is 
recorded in the adjacent tracks. 
FIGS. 13A and 13B show one example of a format of the ID section of this 
embodiment together with a read gate signal of a controller for 
reproducing ID data. In this embodiment, since the recording positions of 
ID information in odd number tracks and even number tracks are recorded in 
a different phase relation, timing for reproducing ID information is 
changed at each of the odd tracks and the even tracks. A GAP 6 for 
changing various kinds of gate signals is provided as required. A width 
(W) recording ID information is equal to a record width (Tp: the same as 
the track pitch since the guard band is omitted in this case) in the data 
area. 
Both sides of the area where ID information is recorded is formed as an 
erased area. Then, regarding means for erasing, there can be suitably 
selected a DC erase, an AC erase, etc. The AC erase is preferable as 
described later. Erasing may be performed at the time of formatting. Or, 
the front surface may be erased prior to the format. Or, in a case that a 
magnetic state of the magnetic disk before formatting is substantially 
equivalent to the erase state, recording may be performed based on the 
format as shown in FIGS. 13A and 13B. 
The second area, which is used to write ID information, is needed. However, 
since the amount of data of the ID section is originally slight, the 
reduction of the format efficiency can be disregarded. Therefore, there 
can be obtained an advantage in the improvement of reliability and the 
density of the track. 
A first modification of the magnetic disk drive of the first embodiment of 
the present invention will be explained with reference to FIGS. 14A to 
15B. In FIGS. 14A to 15B, the explanation of the portions common to FIGS. 
12A to 13B is omitted. 
In this modification, the positioning offset is provided to the magnetic 
head such that the write head is set to be on-track in the data area at 
the write operation and the read head is set to be on-track in the data 
area at the read operation. Then, in order that the read head is included 
even when the read head is set to be in an off-track state at the 
recording mode, the record width (W) of the ID section is made wider than 
the record width (Tp) of the data section. Due to this, since the read 
head is always presented in the track in which ID information is recorded, 
and reads ID information, information of the ID section can be stably read 
at both write and read operations. 
In addition, similar to the first embodiment, since both sides of the ID 
section are erased, there is brought about an advantage in which the 
off-track margin is wide in the case that the head is off-track by various 
types of noise and disturbance. 
Regarding the above-mentioned wide ID information area, for example, ID 
information is recorded with the same width as the data section, a 
predetermined amount of offset is added to the head, the phases are 
correctly arranged, and recorded ID information is overwritten to the 
previously written information, whereby, the above-mentioned wide ID 
information area can be obtained. 
A second modification of the magnetic disk drive of the first embodiment of 
the present invention will be explained with reference to FIGS. 16A to 
17B. In FIGS. 16A to 17B, the explanation of the portions common to FIGS. 
12A to 13B is omitted. 
In this modification, the record width (W) of the ID section is the same as 
the case of FIGS. 12A to 12C. However, a predetermined amount of offset 
(.DELTA.) is added to the head at the ID information write operation so as 
to record ID information. The amount of offset (.DELTA.) is fixed such 
that ID information is recorded at substantially the center between the 
read head position at the write operation and the read head position at 
the read operation. 
Similar to the above embodiment, the positioning offset is provided to the 
magnetic head such that the write head is set to be on-track in the data 
area at the write operation and the read head is set to be on-track in the 
data area at the read operation. In this case, the provision of the 
positioning offset to the magnetic head is that the read head reads 
information in an off-track state, which is equal to the recording track 
of ID information at both the write and read operations. Then, there is no 
generation in which either the write operation or the read operation is 
disadvantageous in terms of S/N, and as a general, reliability of the 
device can be improved. 
Similar to the first embodiment, since both sides of the ID section are 
erased, there is brought about an advantage in which the off-track margin 
is wide in the case that the head is off-track by various types of noise 
and disturbance. 
FIG. 18 is an outline view of the magnetic disk drive of the second 
embodiment of the present invention. 
In this embodiment, there is used the magnetic disk 3 in which a servo 
signal for head positioning is recorded in the data surface. The composite 
magnetic head 1 is attached to the rotary actuator 2. The movement of the 
rotary actuator 2 is controlled in a radial direction of the magnetic disk 
3 by a VCM (voice coil motor) 6 in accordance with a track position 
control signal sent from a tracking servo circuit 12. The tracking servo 
circuit 12 controls the positioning of the composite magnetic head 1 in 
accordance with servo information reproduced through a 
recording/reproducing circuit 13, in order that the write head is on-track 
in the data area on the magnetic disk 3 at the write operation, and the 
read head is on-track in the data area at the read operation. 
On the magnetic disk 3, there are provided an area where cylinder number 
information is recorded, and an area where sector number information is 
recorded. It is assumed that at least one of cylinder number information 
and sector number information is recorded with a width larger than a track 
pitch. The device of this embodiment has a defect information storage 
memory 15 comprising a nonvolatile solid memory for storing a defect 
sector on the magnetic disk 3 and defect track information. The defect 
sector on the magnetic disk 3 and defect track information may be stored 
in a specific area on the magnetic disk 3. 
In the conventional magnetic disk drive, it is needed that ID information 
(cylinder number, head number, sector number, and presence or non-presence 
of the defect) recorded in the head of each sector should be read before 
processing the data area even when the recording or read operation is 
performed. In contrast, according to this embodiment, since there is 
provided an area where cylinder number information is recorded close to an 
area where servo information is recorded, the cylinder number can be 
detected and confirmed. Then, since there is provided an area where sector 
number information is recorded in the front of each data sector, it is 
possible to confirm the sector number before the recording or read 
operation. 
Moreover, in the device of this embodiment, in order to store the defect 
sector on the disk and defect track information into the memory 10, the 
defect sector and defect track information are read from the memory 10 at 
the time of starting the device, thereby making it possible to confirm 
whether the sector to be accessed is a defect sector or not beforehand 
without accessing. The head number does not have to be written to the ID 
section if a physical head number and a logical head number are the same. 
In some magnetic disk drives, there is a case that the logical head number 
seen from the outer unit, the cylinder number and the sector number are 
different from the logical head number, the cylinder number and the sector 
number, which are recorded on the disk. This case can be dealt with by 
providing an allocation table is to a suitable memory. Therefore, the head 
number can be confirmed without recording it to the ID section. 
In this embodiment, it is needed that a hard disk controller 14 (HDC) for 
controlling the recording/producing circuit 13 be changed for the 
conventional HDC. However, processing can be performed by use of ID 
information (cylinder number, sector number, head number and detect 
information), which is sequentially confirmed by a different timing, by 
the above-mentioned method in accordance with a condition of interface. In 
a case that the conventional IC for HDC, serving as HDC 14, is used, a 
suitable circuit is added thereto, and a signal may be transmitted by the 
same timing when the conventional ID section is read before the 
recording/reproducing is performed in the data area. 
According to the above-mentioned embodiment, even if a format in which the 
ID section is omitted is used in the magnetic disk 3, all necessary ID 
information can be confirmed prior to the data write operation. 
In recent years, the so-called sector servo system, which is popularly used 
in a data surface servo system, has been mainly used in accordance with 
improvement of track density. In a recording system at the same transfer 
rate from the outer circumference to the inner circumference, the servo 
sector and the data sector are the same in almost all cases. In the case 
where both are the same, for example, servo data, cylinder number 
information, and sector number information are sequentially stored, and 
the data area continues after a suitable gap is provided for changing the 
recording/reproducing circuit. 
In contrast, in so-called CDR (Constant Density Recording) system in which 
the data area is divided into several zones, the transfer rate is 
increased in the outer circumference zone, and the recording is performed 
at substantially the same recording density through the inner and outer 
circumferences so as to increase the capacity of data, there is a case 
that both the servo sector and the data sector do not conform to each 
other. In such a case, cylinder number information is recorded 
sequentially after servo information of each servo sector, and sector 
number information is recorded in the head of each of the data sectors 
through a suitable gap for changing the recording/reproducing circuit. 
If the phases of sector number information are arranged (the phases are 
arranged in the zone in the case of CDR) and recorded, it is advantageous 
that completely the same data can be read by the recording/reproducing 
track misregistration even if the head is off-track. 
Among the above ID information, cylinder number information and sector 
number information can be recorded at the same time at the servo write 
operation. In this way, by recording the cylinder number information and 
sector number information at the same time at the servo information write 
operation, the phases and the tracks can be correctly adjusted and 
recorded similar to servo information. Unlike ID information recorded at 
the time of the format in the prior art, highly accurate recording in 
which the phase is controlled can be performed. Moreover, a time for 
recording an ID section when formatting the disk can be omitted, and there 
can be obtained an advantage in which a formatting efficiency can be 
improved. The method for recording cylinder number information will be 
explained in an embodiment described later. 
As means for realizing the head tracking servo, which can position the 
magnetic head such that the write head is on-track in the data area at the 
write operation and the read head is on-track in the data area at the read 
operation, there may be used a servo pattern in which a head positioning 
servo signal for recording and a head positioning servo signal for 
reproducing are separately written. Or, in order to compensate for the 
recording/reproducing track misregistration, an offset may be provided to 
position the head. The following embodiment mainly describes a case in 
which the offset is provided. 
A first specific example of the second embodiment will be explained with 
reference to FIGS. 19A to 20B. 
As shown in FIG. 18, when the composite head, in which the write head and 
the read head are structured in a composite form, is applied to the 
magnetic disk drive on which the rotary actuator 2 is mounted, if the 
composite magnetic head 1 is moved from the inner track of the magnetic 
disk 3 to the outer track of the magnetic disk 3 by the rotation of the 
rotary actuator 2, as shown in the right side of each of FIGS. 19A to 19C, 
each of the position of the write head (shown by W in the figure) and the 
position of the read head (shown by R in the figure) generates a position 
misregistration in the track area. 
If n is set to a natural number greater than or equal to 2, cylinder number 
information is recorded in different phase relationships in accordance 
with a remainder obtained when the cylinder number is divided by n. 
Regarding the setting the natural number, in consideration of the 
recording/reproducing track misregistration, head width tolerance, and 
amount of random off-track, if the width with which the read head can read 
information is set to X, n may be selected such that n.multidot.TP&gt;X 
(Tp=track pitch). When the recording/reproducing track misregistration is 
small, n=1, cylinder number information, which is recorded in the full 
width of the track pitch, is used. 
FIGS. 19A to 19C show the case of n=2. That is, these figures show the 
positional relationship between the cylinder number area format and the 
head in the outer circumference section of the magnetic disk, central 
section, and odd tracks of the inner circumference section. The 
positioning offset is provided to the magnetic head such that the write 
head is set to be on-track in the data area at the write operation and the 
read head is set to be on-track in the data area at the read operation, 
thereby making it possible to perform write/read operations in the data 
area. In this case, the cylinder number section is read in a state that 
the read head is off-track at the time of the recording mode. However, 
since the cylinder number section has a width twice as large as the track 
pitch, there is brought about an advantage in which an off-track margin is 
larger than a conventional method in which data are recorded in the 
adjacent tracks. 
FIGS. 20A and 20B show an example of the cylinder number section format in 
this embodiment together with a read gate signal of a controller for 
reproducing the cylinder number section. 
In this embodiment, since the recording positions of cylinder number 
information in odd number tracks and even number tracks are recorded in 
different phases, timing for reproducing cylinder number information is 
changed at each of the odd tracks and the even tracks. A GAP 6 for 
changing various kinds of gate signals is provided as required. 
In the width (W) for recording cylinder number information, since the same 
recording as the servo signal can be performed, the phases are arranged as 
information is sent in a radial direction with a half pitch of the track 
pitch, and overwritten, so that cylinder number information is recorded in 
the width of the full of the track pitch. Therefore, cylinder number 
information can be recorded with a wider recording width than the 
recording width of the data area (in the figures, since the guard band is 
omitted, the same width is shown), which is determined by the width of the 
recording head. About twice the area, which is used to write cylinder 
number information, is needed. However, since the amount of data of the 
cylinder number area is originally slight, there can be larger advantage 
in the improvement of the format efficiency due to the omission of the ID 
section. Moreover, there can be obtained an extremely large advantage in 
the improvement of reliability and the track density. 
FIGS. 21A to 22B show the positional relationship between a cylinder number 
area format and the head in the track of each of the outer circumference 
section, center circumference section, and inner circumference section. In 
order that the write head is set to be on-track in the data area at the 
write operation and the read head is set to be on-track in the data area 
at the read operation, the positioning offset is provided to the magnetic 
head, thereby making it possible to perform read/write operations in the 
data area. In this case, in order that the write head is set to be 
on-track state in the data area at the write operation and the read head 
is set to be on-track in the data area at the read operation, the 
positioning offset is provided to the magnetic head. In addition, there 
are provided first cylinder number information, which is recorded at a 
position where the read head is set to be on-track at the data read 
operation, and second cylinder information, which is recorded at a 
position where the read head is set to be on-track at the data write 
operation. Due to this, in any case, the read head can reproduce the 
cylinder number section in a state that the read head is on-track, and 
cylinder number information can be stably read at both write and read 
operations. 
A third specific example of the second embodiment will be explained with 
reference to FIGS. 23A to 24B In this example, servo information is read 
by the read head so as to realize a head tracking servo, which can 
position the magnetic head such that the write head is set to be on-track 
in the data area at the write operation and the read head is set to be 
on-track in the data area at the read operation. There are provided first 
servo information, which is recorded such that the write head is set to be 
on-track in the data area at the write operation, and second servo 
information, which is recorded such that the read head is set to be 
on-track in the data area at the read operation. Thereby, the write/record 
heads can be correctly set to be on-track at the recording/write 
operations, respectively. 
A magnetic disk drive of a third embodiment of the present invention will 
be explained with reference to FIGS. 25A and 25B. 
According to the third embodiment, the ID area is divided into two areas of 
odd and even tracks, and the width of each ID area is set to an integral 
multiple of a pitch width of the servo positioning. In other words, as 
shown in FIG. 25A, the width of each of the ID areas is set be twice as 
large as the pitch width of the servo positioning. In this case, for 
example, the odd ID area has an width in which servo positioning pitches A 
and B are added. Thereby, since there is no need that ID information is 
overwritten with a half pitch of the write head, time for recording ID 
information can be shortened. 
A magnetic disk drive of a fourth embodiment of the present invention will 
be explained with reference to FIG. 26. FIG. 26 is a diagram showing that 
a servo pattern is recorded in the present invention. 
Prior to recording the servo pattern onto the magnetic disk 3, an index, 
serving as a reference and a clock for servo signal are written into the 
track (hereinafter called as a servo clock track), which is fixed on the 
magnetic disk 3, by use of a clock head 7 in order to record the servo 
pattern generated by a clock generating circuit for separating the index 
signal from the servo signal. At the servo pattern write operation, the 
index signal for obtaining timing to record the servo pattern and the 
clock for servo signal are reproduced by the clock head 7. 
A clock separating circuit 27 for index and servo signals separates the 
clock for index and servo signals from a reproducing signal sent from the 
clock head 7, and transmits the signal to a servo pattern generating 
circuit 25. The servo pattern generating circuit 25 generates a signal for 
recording the servo pattern based on timing due to the clock for index and 
servo signals. At this time, burst pattern data in a positioning data area 
are generated based on the clock for servo signal. However, in an AC 
signal area other than the burst pattern of positioning data, the servo 
pattern is structured in accordance with the clock having a higher 
frequency than the frequency of the burst pattern generated by a clock 
generating circuit 26 for AC signal. A series of the servo pattern 
recording signal, which is structured by the servo pattern generating 
circuit 25, is sent to an recording/reproducing amplifier for the servo 
pattern recording, and recorded onto the magnetic disk 3 by the write head 
of the MR head. 
The position of the head is detected by a head position detecting circuit 
23 using a laser measuring device. A head position control circuit 22 
generates a head position control signal by use of a signal showing the 
head position. An actuator driver 21 is driven, and the servo pattern is 
recorded as the head is sent. Thereby, a predetermined servo pattern is 
recorded on the entire circumference of the magnetic disk. 
FIG. 27 is a block diagram showing a generating circuit in a case that the 
servo pattern recorded by the device of FIG. 26 is used. 
The reproducing signal reproduced by the MR head from the magnetic disk is 
amplified by a recording/reproducing amplifier, and sent to a servo 
area/data area discriminating circuit 30, a data reproducing circuit 31, 
and a burst signal separating circuit 32. The reproducing signal, which is 
recognized as a data area by the servo area/data area discriminating 
circuit 30, is modulated by the data reproducing circuit 31, and 
transmitted as producing data. The reproducing signal, which is recognized 
as a servo area by the servo area/data area discriminating circuit 30, is 
passed through a low pass filter or a burst signal separating filter 31 
having a band-pass filter characteristic, information is extracted from 
the burst pattern. Then, information is sent to a servo circuit 33, and 
used in controlling the head position. 
FIG. 28 is an example showing a recording pattern of a burst portion A and 
that of a burst portion B. Similar to the burst portions A and B, in burst 
portions C and D, the portion other than the burst portions is recorded by 
the AC signal having a higher recording frequency than the burst portions. 
The AC signal portion does not need to adjust to the phase every half 
track pitch. 
A fifth embodiment of the present invention will be explained with 
reference to FIGS. 29A to 30B. FIGS. 29A to 30B show the positional 
relationship between an ID area format and the head in the track of each 
of the outer circumference section, center circumference section, and 
inner circumference section. In order that the write head is set to be 
on-track in the data area at the write operation and the read head is set 
to be on-track in the data area at the read operation, the positioning 
offset is provided to the magnetic head, thereby making it possible to 
perform read/write operations in the data area. 
According to this embodiment, there are provided first ID information, 
which is recorded at a position where the read head is set to be on-track 
at the read operation, and second ID information, which is recorded at a 
position where the read head is set to be on-track at the write operation. 
Thereby, the read head reads the ID section in a state that the read head 
is on-track at the write/read operations, so that information of the ID 
section can be stably read at both write and read operations. 
FIGS. 30A and 30B show an example of the ID section format in this 
embodiment together with a read gate signal of a controller for 
reproducing the ID section. In this embodiment, since the recording 
position of ID information is different in the write and read operations, 
timing for reproducing ID information is changed at each of the write and 
read operations. 
A sixth embodiment of the present invention will be explained with 
reference to FIGS. 31A to 32B. FIGS. 31A to 31C show the positional 
relationship between an ID area format and the head in the track of each 
of the outer circumference section, center circumference section, and 
inner circumference section. In order that the write head is set to be 
on-track in the data area at the write operation and the read head is set 
to be on-track in the data area at the read operation, the positioning 
offset is provided to the magnetic head, thereby making it possible to 
perform read/write operations in the data area. 
According to this embodiment, at the data read operation, the read head 
reads first ID information, which is recorded by the format suitable for 
reproducing by use of the read head, in the on-track state. At the data 
write operation, the write head reads second ID information, which is 
recorded by the format suitable for reproducing by use of the read head 
and different from first ID information, in the on-track state. Thereby, 
information of the ID section can be stably read at both write and read 
operations. 
In the composite head, the write head is naturally inferior to the read 
head in the ability of reproduction. Due to this, it is needed that second 
ID information read by the write head be by a suitable format for 
reproducing information in which a linear record density is made lower the 
first ID information for the head and redundancy is provided (for example, 
strong ECC (error correction code)) by use of the write head. 
FIGS. 32A and 32B show an example of the ID section format in this 
embodiment together with a read gate signal of a controller for 
reproducing the ID section. In this embodiment, since the recording 
position of ID information is different in the write and read operations, 
timing for reproducing ID information is changed at each of the write and 
read operations. Generally, since conditions such as the frequency band of 
the filter and a constant of an equalizer are different in the case that 
the signal is read by the read head and the case that the signal is read 
by the write head, the reproducing circuit system or the constant of the 
circuit is preferably changed to be suitable for each case. 
A seventh embodiment of the present invention will be explained with 
reference to FIGS. 33A to 33C, and 34. FIGS. 33A to 33C show the 
positional relationship between an ID area format and the head in the 
track of each of the outer circumference section, center circumference 
section, and inner circumference section. In order that the write head is 
set to be on-track in the data area at the write operation and the read 
head is set to be on-track in the data area at the read operation, the 
positioning offset is provided to the magnetic head, thereby making it 
possible to perform read/write operations in the data area. 
According to this embodiment, ID information, which is recorded at 
relatively low record density as compared with the data area and can be 
read even by the read head or the write head, can be read by the read head 
in a state that the read head is in an on-track at the read operation and 
by the write head in a state that the write head is off-track at the write 
operation. Due to this, information of the ID section can be stably read 
at both write and read operations. 
In the composite head, the write head is naturally inferior to the read 
head in the ability of reproduction. Due to this, it is needed that second 
ID information read by the write head be by a suitable format for 
reproducing information in which a linear record density is made lower the 
first ID information for the head and redundancy is provided (for example, 
adding strong ECC (error correction code)) by use of the write head. 
FIG. 34 shows an example of the ID section format in this embodiment. In 
this embodiment, since common ID information is read at both write and 
read operations, it is unnecessary to change timing for reproducing ID 
information at the write and read operations. Generally, since conditions 
such as the frequency band of the filter and a constant of an equivalent 
circuit are different in the case that signal is read by the read head and 
the case that the signal is read by the write head, the reproducing 
circuit system or the constant of the circuit is preferably changed to be 
suitable for each case. 
FIG. 35 shows an enlarged view showing the arrangement of servo information 
on the magnetic disk of an eighth embodiment. In this embodiment, first 
servo information 36 corresponding to the read head and second servo 
information 37 corresponding to the write head are alternately and 
dispersively recorded in a direction of a recording track 35, that is, a 
disk rotating direction (shown by .theta.). Each of first and second servo 
information 36 and 37 is used to position each of the read head and the 
write head. 
FIG. 36 shows an enlarged view of servo information shown in FIG. 35. In 
this figure, there are formed a servo area where first and second 
information for recording and reproducing position information are 
recorded, and an ID section 1 and an ID section 2 for recording and 
recording through a gap GAP. Since the ID section is normally read at both 
write and read operations, two ID sections 1 and 2 are provided for 
recording and reproducing. In the servo area, there is recorded 
discrimination information of 0 or 1 for discriminating whether servo 
information is first servo information (for recording) or second servo 
information (for reproducing). Discrimination information may be provided 
in either ID section 1 or ID section 2. However, discrimination 
information is preferably written in the servo area as mentioned above so 
as to prevent information of ID section 1 and ID section 2 from being 
increased. 
Since the ID sections are dispersively recorded, the ID sections cannot be 
read if the position of the track and that of the head misregister. Due to 
these, two ID sections for recording and reproducing are used. Since servo 
information is written by a continuous recording system, servo information 
can be read if the position of the track and that of the head misregister. 
Due to this, position information for recording and reproducing appearing 
alternately can be read by one head. 
FIG. 37 shows an example showing the structure of a position information 
generating circuit, and showing the portions of the recording/reproducing 
circuit 13 of FIG. 18 and the tracking servo circuit 12, which are related 
to this embodiment. 
The reproduced signal 30 is a signal, which is read from the magnetic disk 
of FIG. 36 by the read head, and includes first and second servo 
information. The reproduced signal 30 is inputted to a signal separating 
circuit 41. Then, position error information X, which includes first and 
second position error information obtained from first and second servo 
information by the well-known means, and a control signal C, which 
includes the discrimination signal for discriminating whether servo 
information is used for reproducing or recording, are separated from each 
other. In this case, first and second position error information is 
information showing the position error of each of the write head and the 
read head. A CPU 43 receives the control signal C from the signal 
separating circuit 41, and controls the entire device. 
Position error information C sent from the signal separating circuit 41 is 
sampled with a sampling rate Fs (sampling frequency) by an A/D converter 
42 including a Zeroorder holding circuit, and converted to a digital 
signal. Thereafter, the digital signal is inputted to a band rejection 
filter (BRF) 44, which cuts a frequency component of Fs/2. Then, a low 
frequency component including a DC component is cut by a high-pass filter 
(HPF) 45, so that first position information Xi is generated. 
A selector 46 selects either first position error information, which shows 
the position error of the read head, or second position error information, 
which shows the position error of the write head, in accordance with a 
select control signal generated by the CPU 43 based on discrimination 
information. Position error information selected by the selector 46 is 
inputted, and the high frequency portion whose phase component is 
distorted is cut, so that second position information X2 is generated. 
An adder circuit 48 adds and synthesizes first and second position 
information X1 and X2, and outputs third position information X3. In this 
case, the cutoff frequency of the high-pass filter 45 and that of the 
low-pass filter 47 (low cut-off frequency and high cut-off frequency) are 
conformed to each other, whereby first and second position information X1 
and X2 are smoothly synthesized. Third position information X3 is formed 
by synthesizing first position information X1 including no DC component 
with second position information X2 having little AC component. In third 
position information X3, there is no component of Fs/2. However, third 
position information is substantially the same as position information of 
sampling rate Fs, and there is little phase distortion up to the high 
frequency. Third position information X3 is fed back to VCM 11 of FIG. 18 
through a VCM driver (not shown), and positions the composite magnetic 
head 1 to a predetermined position. 
The above embodiments explained the case of dealing with the track 
misregistration due to the skew angle. In addition, it is obvious that the 
embodiments of the present invention can perform the functions described 
below. More specifically, in order to deal with deterioration of the 
signal generated by the recording/reproducing track misregistration caused 
by misregistration of the mask position during the step of laying the 
write head and the head, an offset is provided to the head in accordance 
with misregistration of the write head and the read head and formatting is 
performed. The above-mentioned point is included in the feature of the 
present invention. 
A more preferably manner of write/read composite head for improving a track 
density will be explained. In the following explanation, a portion of only 
the write head of the composite head will be illustrated and explained 
except where needed. 
FIGS. 38A and 38B are schematic diagrams for explaining a side fringing 
phenomenon occurred at write operation with a ring-type head. FIG. 38A 
shows the case that skew angle is zero, FIG. 38B shows the case that the 
skew is .theta.. A closed curve A shown in each of FIGS. 38A and 38B shows 
an example of equivalent magnetic field curve having recording magnetic 
field equal to coercivity (Hc) on the surface of the magnetic disk. 
It is common knowledge that magnetization of the magnetic disk is reversed 
by enlarging an intensity of the magnetic field of the head equal to or 
larger than Ha of the magnetic disk. Accordingly, an inner portion of the 
closed curve A is changeable area of the magnetization and final recording 
state is basically determined by the magnetic field of the trailing edge 
of the head. 
Since broad magnetic field is formed in a outside portion of the edge 
opposite to the magnetic disk, a formed flux reversal becomes broad. In 
addition, it has a problem such that a reversal position is different from 
the regular position and a noise of the magnetic disk is large. These 
phenomena are called as side fringing and are important factors of 
narrowing an effective recording area, thereby obstructing an improvement 
of the track density. 
When a recording is performed by using the abovementioned head, an 
influence of the side fringing is the same at the right and left sides of 
the head (f.sub.R =f.sub.L =f.sub.O) at which a skew angle is zero. When a 
skew angle is not zero, a width of trailed area by side fringing magnetic 
field is widened and a normal recorded area is finally narrowed by the 
trailing edge at another edge. Therefore, an invalid area is extremely 
extended (f.sub.L &gt;f.sub.O) 
FIG. 39 is a schematic diagram for explaining a problem occurring during 
recording with a single pole head (SPH) for perpendicular recording. The 
perpendicular recording with SPH has a feature that the side fringing 
effect is extremely small than the in-plane recording with the ring-head, 
since the magnetic field of the edge portion is rapidly reduced. 
The recording by the above-mentioned head having a skew angle has a demerit 
because of recording at the side portion of the head. When a skew angle is 
not zero, a width of trailed area by side of the edge is widened and a 
normal recorded area is not finally performed by the trailing edge at 
another edge. Therefore, an invalid area is extremely extended at a read 
operation. 
In order to solve the above problem, in the present invention, an arbitrary 
portion of the pole of the write head of the leading side is made in a 
shape of the pole being in an area trailed by trailing edge of the write 
head on an arbitrary track from the innermost track to the outermost 
track. The specific examples of the write head is shown in FIGS. 40A to 
43. It is assumed that a skew angle at which the head position determined 
at the outermost track is .theta..sub.out and a skew angle at which the 
head position is determined at the innermost track is .theta..sub.in. For 
convenience, a sign of the angle is determined that .theta..sub.out is 
positive direction and .theta..sub.in is negative direction, relatively. 
FIGS. 40A to 40C show some cases of a ring head. In a case that one of the 
angle of the skew angle .theta..sub.out or .theta..sub.in is 0.degree. or 
the same sign, one of the poles of the reading side may be trimmed. In a 
case that the skew angle is negative at inner circumference side and 
positive at outer circumference side, the head may be trimmed as shown in 
FIG. 40B. The head may be trimmed shown in FIG. 40C for the purpose of 
further loping the side fringing. 
FIGS. 41A to 41C show some cases of an SPH. In the SPH, which is same as 
the ring head, in a case that one of the angle of the skew angle 
.theta..sub.out or .theta..sub.in. is 0.degree. or the same sign, one of 
the pole of the may be trimmed. In a case that the skew angle is negative 
at inner circumference side and positive at outer circumference side, the 
head may be trimmed as shown in FIG. 41B. The head can be trimmed shown in 
FIG. 41C to share up-faced head and down-faced head 
(.vertline..theta.&gt;.vertline..theta..sub.out .vertline., 
.vertline..theta..sub.in .vertline.). 
FIG. 42 shows an example of a trimming of a merged type MR composite head 
and FIG. 43 shows an example of a trimming of an In-Gap type MR composite 
head. In FIGS. 42 and 43, the various shapes can be employed according to 
the sign of skew angles .theta..sub.out, .theta..sub.in and other 
conditions same as FIGS. 40A to 40C. 
The method of trimming is performed as follows. The composite head is made 
in a normal process and a portion except for a selected portion deleted by 
trimming is masked by resist. The resist is removed after trimming, e.g. 
using etching or ion milling. A well-known art such as FIB (Focused Ion 
Beam) processing can be employed as a trimming. 
As described above, by using the above-mentioned write/read composite head 
of the present invention, an improved track density is achieved which 
suppresses the influence of side fringing when using a rotary actuator. 
Additional advantages and modifications will readily occur to those skilled 
in the art. Therefore, the present invention in its broader aspects is not 
limited to the specific details, representative devices, and illustrated 
examples shown and described herein. Accordingly, various modifications 
may be made without departing from the spirit or scope of the general 
inventive concept as defined by the appended claims and their equivalents.