Recording/reproducing apparatus and servo-information recording method

An index determining unit determines that a current position in a disk medium corresponds to a true index when reaching a true index pattern of servo information recorded in the disk medium. The determination is used for reading predetermined servo information so as to perform a servo control operation of a disk reading/writing head. The disk medium has the true index pattern in a first portion of the disk medium and also untrue index patterns of servo information in a predetermined number of second portions in proximity to the first portion along a track direction. The true index pattern and the untrue index patterns form a predetermined sequence. The index determining unit comprises a reading unit for reading the servo information recorded in the disk medium; a storing unit for storing the read servo information in series; and a determining unit for determining that a current position in the disk medium corresponds to the true index when the stored servo information includes a sequence which is different from the predetermined sequence by a predetermined error.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a recording/reproducing apparatus for 
recording servo information on a disk medium, and then reading the servo 
information and performing servo control of a head. 
Recently, due to the increased amount of information being processed in 
computer systems, the amount of information to be stored in a magnetic 
disk apparatus has increased. Therefore, miniaturization and increased 
storage capacities of storage media of information storage apparatuses are 
required. Further, high-density storage media and high-performance 
recording/reproducing apparatuses are demanded. 
2. Description of the Related Art 
FIG. 1 shows a plan view of one example of a magnetic disk apparatus in the 
related art. In the magnetic disk apparatus 11, an actuator 12 includes a 
predetermined number of arms 13 each of which has a magnetic head 14 at a 
projecting end thereof via a supporting-spring mechanism 13a. A base of 
each arm 13 is pivotably supported by a pivot 15. 
A rotational supporting unit 16 is provided at the other end of the arm 13. 
A coil 17 is wound on the rotational supporting unit 16. Magnets 18a and 
18b are fixed below the coil 17. A VCM (Voice Coil Motor) is formed by the 
coil 17 and magnets 18a and 18b. 
A predetermined number of magnetic disks 20 are fixed onto a spindle 19 of 
a sensor-less spindle motor (not shown in the figure) and are rotated. In 
the actuator 12, an electric current flows through the coil 17 via a 
circuit substrate 21 and a flexible print board 22, and thus the arms 13 
are rotated so that each of the heads 14 moves along a radial direction of 
each of the disks 20. 
In this magnetic disk apparatus 11, a seeking control is performed for 
positioning the magnetic heads 14 at predetermined tracks in the magnetic 
disks 20. This seeking control is performed in a closed-loop servo control 
method in which servo information previously recorded on the magnetic 
disks 20 is read for the seeking control. 
A servo-area servo method and a data-area servo method are included in the 
servo control method. In the servo-area servo method, a magnetic disk 
which has the servo information recorded in a special servo area in the 
disk is used. In the data-area servo method, a magnetic disk which has the 
servo information recorded in a data area in the disk is used. 
The servo information is recorded in each track or each sector in the 
magnetic disks 20 at predetermined positions common to the magnetic disks 
20. In order to read predetermined servo information from the magnetic 
disks 20, an index recorded in each track of each of the magnetic disks 20 
is previously detected, index detection thus being performed. A recording 
position of the servo information and then positions of the magnetic heads 
14 are detected based on the detected index. 
FIG. 2 illustrates an index pattern in a magnetic disk in the related art. 
FIG. 2 shows a case of a sector servo method in which sector servo 
information 24 is recorded in each sector of a predetermined track in the 
magnetic disk 20. The sector servo information 24 is recorded, for 
example, in an AGC (Automatic Gain Control information) region 24.sub.1, 
in an SM (Servo Mark information) region 24.sub.2, an ID and INDEX 
(writing and reading index information) region 23.sub.3, and a POSITION 
(position information) region 24.sub.4 shown in FIG. 2. 
Sector servo numbers (for example, 0 through 60) and an index pattern are 
recorded in the ID and INDEX region 24.sub.3. The index pattern is formed 
by a pattern in which "0" is allocated for a position at which the sector 
number is "0" and "1" is allocated for the other positions. The "0" in the 
index pattern acts as an index, and an index pulse is generated when "0" 
is detected. Thus, the above-mentioned index detection is performed. 
Servo information is recorded in each of the magnetic disks 20 in a manner 
in which positions at which the servo information are recorded overlap one 
another between recorded tracks of the disks 20. 
FIG. 3 shows a spatial relationship of the positions between disks 20 in 
the related art at which the servo information is recorded. FIG. 3 shows 
an example disclosed in Japanese Laid-Open Patent Application No. 
2-304784. In this example, the servo information is recorded in the tracks 
TRK0 through TRK3 of the disks 20 in a manner in which the positions at 
which the servo information is recorded overlap one another between the 
tracks TRK0 through TRK3 of the disks 20 in a time series manner. When 
servo information is recorded or written in sectors (0, 0), (0, 1), (0, 
2), and (0, 3) of the tracks TRK0 through TRK3 shown in the figure, a head 
14.sub.0 selected from the magnetic heads 14 writes the servo information 
to the sector (0, 0) of the track TRK0. Then, after the completion 
thereof, a head 14.sub.1 selected from the magnetic heads 14 writes the 
servo information to the sector (0, 1) of the track TRK1. Thus, after 
completion of servo-information writing to one sector, servo-information 
writing to a subsequent sector is performed. In this manner, the servo 
information is written to the four sectors (0, 0) through (0, 3). 
In the related art, as shown in FIG. 2, one index pattern is provided for 
the relevant servo information, and the index detection is performed by 
detecting only the one index pattern. Therefore, if the one index pattern 
is missing for some reason, an index error occurs and any normal operation 
cannot be performed until a subsequent index pattern is appropriately 
detected. Thus, performance of the magnetic disk apparatus is degraded. 
Further, redundancy is not sufficiently high if only one index pattern is 
provided for the relevant servo information. Therefore, an index detection 
margin is not sufficiently high and thus performance degradation may also 
occur by this cause. 
Further, in the related art, as shown in FIG. 3, the positions of the 
relevant servo information overlap one another between the tracks of the 
disks. Therefore, after the completion of servo-information writing on a 
sector of a track of a magnetic disk, it is necessary to wait for 
approximately one rotation of the disks 20 before starting 
servo-information writing to a sector of a track of a subsequent disk. As 
a result, the time required for writing the desired whole servo 
information and for verifying it for the entirety of the disks 20 is a 
considerably long time. In fact, this time results from multiplying the 
time required for writing the servo information for one track by the 
number of servo frames for each track and then multiplying this result by 
the number of cylinders of the disks 20. Thus, the servo-information 
writing or recording work is troublesome. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a recording/reproducing 
apparatus in use of which the index detection margin can be improved, the 
time required for the servo-information recording and verifying can be 
reduced, and thus the performance of the apparatus can be improved. 
A recording/reproducing apparatus according to the present invention 
comprises: 
index determining means for determining that a current position in a disk 
medium corresponds to a true index when reaching a true index pattern of 
servo information recorded in said disk medium, the determination being 
used for reading predetermined servo information so as to perform a servo 
control operation of a disk reading/writing head; 
said disk medium having said true index pattern in a first sector of said 
disk medium and also untrue index patterns of servo information in a 
predetermined number of second sectors in proximity to said first sector 
along a track direction, said true index pattern and said untrue index 
patterns forming a predetermined sequence; and 
said index determining means comprising: 
reading means for reading the servo information recorded in said disk 
medium; 
storing means for storing the read servo information in series; and 
determining means for determining that a current position in said disk 
medium corresponds to said true index when the stored servo information 
includes a sequence which is different from said predetermined sequence by 
a predetermined error. 
It is preferable that said predetermined sequence comprises an arithmetic 
progression formed of numbers represented by said true index pattern and 
said untrue index patterns. 
In the apparatus, a current position in the disk medium can be determined 
to correspond to the true index when the stored servo information includes 
a sequence which is different from said predetermined sequence by a 
predetermined error. Thus, if a small error is included in the read index 
patterns, it is possible to determine that the index patterns include the 
true index. As a result, it is possible to improve an index detecting 
margin and thus to improve an index detecting efficiency. 
It is preferable that said determining means determines that a current 
position in said disk medium corresponds to said true index when the 
stored servo information includes a sequence which is equal to said 
predetermined sequence. 
Further, it is also preferable that said determining means determines that 
a current position in said disk medium does not correspond to said true 
index when the stored servo information includes a sequence which is 
different from said predetermined sequence by a predetermined error. 
Further, it is also preferable that said determining means comprises a 
table which stores conditions to be used for determining that a current 
position in said disk medium corresponds to said true index when the 
stored servo information includes sequences, each of which is different 
from said predetermined sequence by a predetermined error. 
Further, it is also preferable that said determining means comprises means 
for inputting the serially stored servo information in parallel. 
Thereby, it is possible to determine the read index patterns includes the 
true index pattern when the read index patterns completely agree with a 
reference pattern, and when the read index patterns include a 
predetermined error. Further, it is also possible to determine that the 
read index pattern does not include the true index pattern when the read 
index patterns include a predetermined error. As a result, it is possible 
to adaptively perform the index determining operation. 
A recording/reproducing apparatus according to another aspect of the 
present invention comprises: 
reading means for reading servo information from a predetermined number of 
disk media, 
said predetermined number of disk media having said servo information 
recorded therein in a manner in which a position at which said servo 
information is recorded in each of said predetermined number of disk media 
is shifted, when a relevant disk medium is changed, by a distance 
corresponding to a head switching time; and 
servo control means for performing a servo control operation of a 
predetermined number of heads for said predetermined number of disk media, 
using said servo information read from said predetermined number of disk 
media. 
It is preferable that the recording of the servo information in each of 
said predetermined number of disk media is performed in a manner in which 
the servo information recorded in each of said predetermined number of 
disk media through a relevant one of said predetermined number of heads 
includes a head number which is updated every head switching time. 
Further, a servo information recording method according to the present 
invention comprises steps of: 
a) obtaining an index signal from a predetermined number of disk media; 
b) producing a servo-information writing-position signal in response to 
said index signal; 
c) writing servo information in each of said predetermined number of disk 
media through a respective one of a predetermined number of heads at a 
position indicated by said servo-information writing-position signal; and 
d) switching from one to another one among said predetermined number of 
heads after writing the servo information in each of said predetermined 
number of disk media in the step c). 
Thereby, it is possible to perform recording of the servo information or 
verifying the recorded servo information through all the heads in all the 
disk media within a time corresponding to one turn of the disk media. 
Thus, it is possible to improve an operation efficiency in recording the 
servo information and verifying the recorded servo information. 
It is preferable to further comprise head number determining means for 
determining which one of said predetermined number of heads is used for 
currently reading the servo information. 
Further, it is preferable that said head number determining means 
determines which one of said predetermined number of heads is used for 
currently reading the servo information, using a time interval between a 
time an index included in the servo information is reached and a time 
currently read servo information is reached. 
Further, it is preferable that said head number determining means 
determines which one of said predetermined number of heads is used for 
currently reading the servo information, using a time interval between a 
time previously read servo information is reached and a time currently 
read servo information is reached. 
Thereby, it is possible to omit, from the servo information, information 
indicating head numbers. Thus, it is possible to simplify the contents of 
the servo information. 
A recording/reproducing apparatus according to another aspect of the 
present invention comprises: 
reading means for reading servo information from a predetermined number of 
cylinders provided in a disk medium, 
said predetermined number of cylinders having said servo information 
recorded therein in a manner in which a position at which said servo 
information is recorded in each of said predetermined number of cylinders 
is shifted by a predetermined interval when a relevant cylinder is 
changed; and 
servo control means for performing a servo control operation of a 
reading/writing head, using said servo information read from said 
predetermined number of cylinders. 
It is preferable to further comprise cylinder number determining means for 
determining from which one of said predetermined number of cylinders the 
servo information is currently being read. 
Further, it is preferable that said cylinder number determining means 
determines from which one of said predetermined number of cylinders the 
servo information is currently being read, using a time interval between a 
time an index included in the servo information is reached and a time 
currently read servo information is reached. 
Further, it is preferable that said cylinder number determining means 
determines from which one of said predetermined number of cylinders the 
servo information is currently being read, using a time interval between a 
time previously read servo information is reached and a time currently 
read servo information is reached. 
Thereby, it is possible to omit, from the servo information, information 
indicating cylinder numbers. Thus, it is possible to simplify the contents 
of the servo information. 
It is preferable that: 
said predetermined number of cylinders is divided into a predetermined 
number of blocks; and 
the recording of said servo information in each block of said predetermined 
number of blocks is performed in a manner in which a position at which 
said servo information is recorded in each cylinder is shifted, by a 
predetermined interval when a relevant cylinder is changed. 
Thereby, even if a number of the cylinders included in the disk medium is 
increased, an efficient servo-information managing can be performed. 
Other objects and further features of the present invention will become 
more apparent from the following detailed description when read in 
conjunction with the accompanying drawings.

DESCRIPTION OF PREFERRED EMBODIMENTS 
FIG. 4 shows servo information recorded in a predetermined track 32 in a 
magnetic disk 31 as a disk medium according to a first embodiment of the 
present invention. FIG. 4 shows a case of the sector servo method in the 
data-area servo method. However, the first embodiment can also be applied 
to the servo-area servo method. 
In FIG. 4, as mentioned above, as in the sector servo method, the sector 
servo information 33 is recorded in each sector of a predetermined track 
32 of the magnetic disk 31. The sector servo information 33 is recorded, 
for example, in an AGC (Automatic Gain Control information) region 
33.sub.1, in an SM (Servo Mark information) region 33.sub.2, in an ID and 
INDEX (writing and reading index information) region 33.sub.3, and in a 
POSITION (position information) region 33.sub.4. 
Sector servo numbers (for example, 0 through 60) and an index pattern are 
recorded in the ID and INDEX region 33.sub.3. The index pattern is formed 
of index information of each sector servo information 33. The index 
pattern is formed by a pattern in which a reference position is referred 
to as a true index. The reference position is, for example, a position at 
which the relevant sector servo number is "0", and an index signal "0" 
(recorded in 2-bit binary information, and the same hereinafter) is 
recorded at the true index in the index pattern, as shown in FIG. 4. 
As shown in the figure, an index signal "1" (at a position corresponding to 
the sector servo number `60`) and an index signal "2" (at a position 
corresponding to the sector servo number `59`) are recorded as untrue 
index information. These index signals "1" and "2" are recorded in 
proximity of the sector servo information 33a including the index signal 
"0" along a track 32 direction, and they are recorded in the ID regions 
33.sub.3 of the sector servo information 33a.sub.-1 and 33a.sub.-2 along a 
disk 31 rotation direction. Further, an index signal "3" as untrue index 
information is recorded in the ID region 33.sub.3 in sector servo 
information 33a.sub.-3, 33a.sub.-.sub.4, . . . of each of all sectors in 
the same track 32. Thus, along the rotation of the magnetic disk 31, a 
number indicated by the index signal is decremented (from "3" to "2" and 
then to "1", as shown in FIG. 4) in the index pattern as the true index 
position is approached. 
FIG. 5 shows a block diagram of a construction for detecting the true index 
shown in FIG. 4. The construction shown in FIG. 5 is part of a magnetic 
disk apparatus which will be described later. A plurality (2, in FIG. 5) 
of magnetic disks 31 are mounted to a spindle 34a which is rotated by a 
spindle motor (SPM) 34. A relevant one of magnetic heads 35 is provided to 
each one of the plurality of magnetic disks 31. The magnetic heads 35 are 
moved by a VCM (Voice Coil Motor) 36 along radial directions of the 
magnetic disks 31. 
The index information in the sector servo information 33 read through the 
magnetic heads 35 is input to the demodulator 38 acting as reading means 
via an amplifier 37. The demodulator 38 supplies, in series, an index 
demodulated signal to a shift register (SREG) 39 acting as storing means. 
The index demodulated signal is obtained as a result of appropriate 
processing, for example, performing level comparison on the input index 
information. 
The SREG 39 holds the supplied index demodulated signal item by item and 
supplies it as a 4-bit signal (n, n-1, n-2, n-3) to a decoder 40 acting as 
determining means. The decoder 40 is formed of, for example, a logical 
circuit of AND gates (see FIG. 9A), and outputs an index pulse when the 
supplied 4-bit signal agrees with an index pattern for index detection 
(which will be described later). 
The amplifier 37, demodulator 38, SREG 39 and decoder 40 forms an index 
detecting circuit 41. 
FIG. 6 shows an entire block diagram of the magnetic disk apparatus in the 
first embodiment of the present invention. In the magnetic disk apparatus 
51 acting as a recording/reproducing apparatus, the magnetic disks 31 are 
rotated by the SPM 34 at a predetermined rotational speed, and the 
magnetic heads 35 are moved radially along the disk by the VCM 36 acting 
as rotation driving means. 
Each of the magnetic heads 35 is, for example, a composite thin-layer 
magnetic head obtained as a result of combining a thin-layer head for 
recording data and an MR head. 
Data and a servo signal (servo information) read through the magnetic heads 
35 from the magnetic disks 31 are sent, via a head IC 52, to a servo 
demodulating circuit 53, a read/write circuit 54, and an index detecting 
circuit 41. The servo demodulating circuit 53 converts the servo signal to 
a position signal acting as position information, and sends it to an 
analog-to-digital converter (ADC) 55. 
The ADC 55 converts the input position signal to a digital signal, and 
sends it to a DSP (Digital Signal Processor) 56. The DSP 56, from the sent 
signal, produces a digital control signal for driving the VCM 36, and 
sends it to a digital-to-analog converter (DAC) 57. The DAC 57 converts it 
to an analog control signal and sends it to a VCM driving circuit 58. 
Thereby, the VCM 36 is driven. Further, an SPM control circuit 59 is used 
in rotating the SPM 34 at a fixed speed. 
The read/write circuit 54 sends the read data to an MPU (Micro Processor 
Unit) 60, and receives write data from the MPU 60 to supply it to the 
magnetic heads. The MPU 60 is controlled by a control signal from a hard 
disk controller (HDC) 61, which ends various control signals to the MPU 60 
according to commands from a high-rank apparatus. 
A spatial arrangement in the above-described magnetic disk apparatus 51 is 
similar to that shown in FIG. 1. 
FIG. 7 illustrates index detection and FIGS. 8A, 8B, 8C, 8D and 8E 
illustrate an index-detecting position. The index information in the 
sector servo information read through the magnetic heads 35 is input as 
the index demodulated signal to the SREG 39 via the amplifier 37 and the 
demodulator 38. 
When the magnetic heads 35 read the index information of the sector servo 
information 33a.sub.-3 of the sector servo number 58, the index signal "3" 
(n) is output, and also the index signal (n-1, n-2, n-3) of the preceding 
three items of index information are output together as shown in FIG. 8A. 
Thus, a signal indicating an index pattern (3, 3, 3, 3) is output to the 
decoder 40 from the SREG 39. 
Then, when the magnetic heads 35 read the index information of the sector 
servo information 33a.sub.-2 of the sector servo number 59, the index 
signal "2" (n) is shifted, and then the SREG 39 outputs a signal of an 
untrue index pattern (2, 3, 3, 3) to the decoder 40 as shown in FIG. 8B. 
Similarly, at the sector servo number 60, the SREG 39 outputs an untrue 
index pattern (1, 2, 3, 3) as shown in FIG. 8C. At the sector servo number 
0, a continuous-progression index pattern (0, 1, 2, 3) is output by the 
SREG 39 as shown in FIG. 8D. Further, at the sector servo number 1, the 
SREG 39 outputs an index pattern (3, 0, 1, 2) as shown in FIG. 8E. 
When the input index pattern is (0, 1, 2, 3) the decoder 40, outputs the 
index pulse. In other words, the index pulse is output when the magnetic 
heads 35 read the true index signal "0" of the sector servo number 0. 
Thus, the true index can be surely detected. In fact, the index detection 
(detecting of the true index) is performed using not only the true index 
signal "0" but also the adjacent untrue index signals "1", "2", and "3" as 
mentioned above. Therefore, if a signal is missing such that the true 
index signal "0" accidentally appears at an erroneous position in the 
index pattern, such an erroneous true index signal can be prevented from 
causing the decoder 49 to supply the index pulse. 
FIGS. 9A, 9B, and 10 shows constructions for other index detection methods. 
FIG. 9A shows a construction of the decoder 40 and includes five AND 
circuits 40.sub.1, 40.sub.2, 40.sub.3, 40.sub.4 and 40.sub.5, and an OR 
circuit 40a. Further, the decoder further includes a table 40b indicating 
five kinds of index detection conditions shown in FIG. 9B. The SREG 39 
inputs a pattern (n, n-1, n-2, n-3) to the AND circuit 40.sub.1, a pattern 
(n, n-1, n-2) to the AND circuit 40.sub.2, a pattern (n, n-1, n-3) to the 
AND circuit 40.sub.3, a pattern (n, n-2, n-3) to the AND circuit 40.sub.4, 
and a pattern (n-1, n-2, n-3) to the AND circuit 40.sub.5. 
Each of the five AND circuits 40.sub.1 through 40.sub.5 outputs an index 
detection signal to the OR circuit 40a when the input pattern agrees with 
an index pattern of a respective one of the five kinds of the index 
detection conditions of the table 40b shown in FIG. 9B. The OR circuit 40a 
outputs the index pulse when receiving the index detection signal output 
from at least one of the five AND circuits 40.sub.1 through 40.sub.5. 
In this case, a symbol `X` in the index detection conditions in the table 
40b represents `indefinite` (i.e., the item in this slot is irrelevant). 
Therefore, index detection is determined in at least one of four cases, 
namely, a case of a completely correct pattern (0, 1, 2, 3), and four 
cases of one-item-missing patterns (0, 1, 2, X), (0, 1, X, 3), (0, X, 2, 
3), and (X, 1, 2, 3). 
Thus, not only in the case of the completely correct pattern, but also in 
the four one-item-missing cases, the index detection signal is supplied to 
the OR circuit 40a which then outputs the index pulse. In other words, 
even if one of the four items "0", "1", "2", "3" of the completely correct 
pattern (0, 1, 2, 3) is erroneously changed to a different one, the index 
pulse can be output. 
In the decoder 40 shown in FIG. 10, a mask register (MASK REG) 40c is 
provided. Except for this matter, the construction shown in FIG. 10 is the 
same as that shown in FIG. 9A. The MASK REG 40c is used for disabling the 
index detection determination in the one-item-missing cases. The MASK REG 
40c supplies mask conditions to the four AND circuits 40.sub.2 through 
40.sub.5 for one item missing of items of n, n-1, n-2, n-3 and thus the 
index detection determination cannot be performed in specific cases of the 
four one-item-missing cases. 
Especially, when the power is ON in the apparatus, the position of the 
magnetic heads is indefinite. In a starting-up time, masking is performed 
for enabling the index detection determination only when the completely 
correct pattern (0, 1, 2, 3) is supplied. Specifically, when the power is 
ON, the mask register 40c supplies a low-level signal to all of the four 
AND circuits 40.sub.2 through 40.sub.5. As a result, each of these four 
AND circuits outputs a low-level signal. Thereby, only when the AND 
circuit 40.sub.1 receives the completely correct pattern (0, 1, 2, 3), a 
high level is supplied to the OR circuit 40a which then generates the 
index pulse. 
As a result, if a signal is missing when the power is ON, the mask register 
40c prevents the index detection determination from being performed. Thus, 
it is possible to perform certain index detection. 
In a steady operation state, the mask register 40 c, supplies a high-level 
signal to each of the four AND circuits 40.sub.2 through 40.sub.5, and 
thus the five kinds of the index detection conditions shown in FIG. 9B are 
used. 
Thus, by making predetermined parts in the index pattern indefinite and 
masking this indefiniteness, it is possible to improve redundancy and thus 
the index detection margin can be improved. As a result, performance of 
the index detection can be improved. 
In the above embodiment, a case where the index pattern (. . . , 3, 2, 1, 
0, 3, 3, . . . ) is recorded in the ID and INDEX region 33.sub.3 in each 
of sector servo information is shown. However, the index pattern is not 
limited to this, and instead, for example, an index pattern (. . . , 5, 4, 
3, 2, 1, 0, 5, 5, . . . ) including a longer continuous progression (5, 4, 
3, 2, 1, 0 ) can be used. Further, a numeral change when approaching the 
true index is not limited to the decrementing manner such that of 3, 2, 1, 
0, and instead, a pattern including a numeral change in an incrementing 
manner, for example, (. . . , 0, 1, 2, 3, 4, 5, 0, 0, . . . ) can be used. 
In this case, the index pattern corresponding to the sector number 0 is 
"5". 
A method is disclosed in Japanese Laid-Open Patent Application No. 6-96560 
for recording a non-zero-code incrementing sequence in a number of data 
frames prior to a relevant index frame in a servo area. In this method, 
for an index "7" (in a 5-bit pattern and 3-bit binary representation), an 
incrementing sequence "1", "2", "3", "4", . . . is recorded starting from 
6 data frames prior to the index frame. Further, "0" is recorded in the 
other positions. In the method, by detecting the non-zero-code 
incrementing sequence, the index frame is detected. 
However, in this disclosed method, the index frame is detected by detecting 
the pattern (1, 2, 3, 4, 5, 6, 7), and the pattern cannot be detected if 
one signal is missing of the seven numerals. Thus, redundancy is 
disadvantageously small. 
FIG. 11 shows part of a magnetic disk apparatus 51.sub.A in a second 
embodiment of the present invention. In the apparatus, the magnetic disks 
31 are mounted on the spindle 34a as shown in the figure, and a plurality 
of data areas provided on recording surfaces of the magnetic disks 31 have 
servo information recorded thereon. For the recording surfaces of the 
magnetic disks 31, the plurality of magnetic heads (HD0, HD1, . . . ) 35 
are provided. Each of the magnetic heads 35 is connected to the head IC 52 
which controls reading/writing operations through the magnetic heads 35. 
A reproduced signal of the servo information obtained using the magnetic 
heads 35 is sent to a servo demodulator 53a via the head IC 52. Thus, the 
various servo information is demodulated. When the servo information is 
written in the magnetic disks 31, the index signal which is detected from 
the magnetic disks 31 is sent to a formatter 62. The servo demodulator 53a 
has a construction including components corresponding to the index 
detecting circuit 41, servo demodulator 53, and ADC 55 shown in FIG. 6. 
The formatter 62 counts sectors using the input index signal, and produces 
a servo-information writing-position signal which is then sent to a head 
selecting circuit 63. Further, the formatter 62 sends a read/write gate 
signal to a read/write (R/W) controller 54. The head selecting circuit 63 
selects one of the magnetic heads 35 by which the servo information is to 
be written, and thus causes the head IC 52 to switch heads to the selected 
one. The read/write controller 54 supplies the input servo information to 
the selected one of the magnetic heads 35 in response to the supplied 
read/write gate signal. 
FIGS. 12A, 12B and 12C illustrate the servo-information writing by the 
magnetic disk apparatus shown in FIG. 11. The formatter 62 produces the 
servo-information writing-position signal from the index signal supplied 
by the servo demodulator 53a. When the servo-information writing-position 
signal is active, the read/write controller 54 starts writing the servo 
information 67.sub.1 using the selected one (HD0) of the magnetic heads 35 
on a relevant one of the magnetic disks 31. In the writing, as shown in 
FIG. 12A, the servo information 67.sub.1 (which will be described later) 
is written from a position of the index IND. 
When the writing of the servo information through the magnetic head HD0 is 
finished, the formatter 62 outputs a head change signal to the head 
selecting circuit 63, and thus, a number of a selecting head is 
incremented so that the selected head is changed from the HD0 to HD1. 
Then, the head HD1 of the magnetic heads 35 is used for writing the servo 
information 67.sub.1 to a relevant one of the magnetic disks 31 as shown 
in FIG. 12A. Similarly, a selected one of the magnetic heads 35 is changed 
in turn to the head HDn so that all the heads of the magnetic heads 35 are 
used to write the servo information 67.sub.1 on all the recording surfaces 
of the disks 31. 
This writing of the servo information 67.sub.1 is illustrated in FIG. 12B. 
As shown in the figure, after a time interval of a head change time has 
elapsed since the head HD0 was used for writing the servo information 
67.sub.1 in a relevant one of the magnetic disks 31, the head HD1 is used 
for writing the servo information 67.sub.1 on a relevant one of the 
magnetic disks 31. 
After all of the magnetic heads 35 (HD0 through HDn) are used for writing 
the servo information 67.sub.1, the selected one of the magnetic heads 35 
is returned to the head HD0, which is then used for writing servo 
information 67.sub.2 similarly. Thus, as shown in FIG. 12C, n items of 
servo information 67.sub.1 through 67.sub.n, relevant to a full circle of 
the magnetic disks 31, are written in each recording surface of the 
magnetic disks 31. In this writing, the head to be used is changed among 
the magnetic heads 35, and a relevant item of the servo information is 
written for each servo frame interval. Thus, the n items of the servo 
information 67.sub.1 through 67.sub.n are written in all cylinders of the 
magnetic disks 31 in a staggered manner. (It is noted that using the same 
symbol `n` for representing the numbers does not mean that the number of 
the magnetic heads should have a specific relationship with the number of 
the items of the servo information.) 
Thus, the servo-information writing using all the magnetic heads 35 (HD0 
through HDn) can be performed while the magnetic disks 31 turn once or are 
rotated a full circle. As a result, the writing for all the cylinders can 
be performed in a time period resulting from multiplying the number of 
servo frames for each track by the number of the cylinders. Thus, it is 
possible to reduce the time required for recording the servo information. 
Further, verification of the written servo information can be also 
performed by reading the written servo information as the head to be used 
is similarly changed among the magnetic heads. 
The time interval of the head change time shown in FIG. 12B may be 
determined using a counter or the like. In this case, the time interval is 
determined such that all the head changes are completed within the servo 
frame interval shown in FIG. 12C. 
An example of the servo information to be written is shown in FIG. 13. As 
shown in the figure, The servo information 67 (each of 67.sub.1 through 
67.sub.n) includes, for example, a read/write (R/W) recovery region 67a, a 
servo mask (SM) region 67b, a head number region 67c, a cylinder number 
region 67d, a position (position information) region 67e, and so forth. A 
head number (indicating one of HD0 through HDn) of the head number region 
67c is appropriately updated when relevant servo information is written to 
a relevant magnetic disk. The updating is performed such that when 
writing, the read/write circuit 54 shown in FIG. 11 receives the relevant 
servo information, replaces a head number of the head number region of the 
relevant servo information with a subsequent head number, and then 
re-forms the relevant servo information including the replaced head 
number. The reformed servo information is then written in the relevant 
magnetic disk. 
FIG. 14 shows part of a magnetic disk apparatus 51.sub.B in a third 
embodiment of the present invention. In this apparatus, the index signal 
from the servo demodulator 53a is sent to a counter 71 as well as to the 
formatter 62. Servo clock pulses are also input to the counter 71 which 
then counts the servo clock pulses after the index signal is input (that 
is, after the true index is reached). A latch circuit 72 holds a resulting 
count number of the counter 71 in response to a servo mark signal from the 
servo demodulator 53a. A head number determining circuit 73, acting as 
head number determining means, is used for determining the head number 
from an output of the latch circuit 72. The other construction is the same 
as that of the construction shown in FIG. 11. The head number determined 
by the head number determining circuit 73 is sent to the MPU 60. A head 
number table 74 (see FIG. 16) is provided with the head number determining 
circuit 73. 
A cylinder number determining circuit, acting as cylinder number 
determining means, which will be described in a description of a fourth 
embodiment of the present invention) may be provided with the head number 
determining circuit 73. 
In the above-described case in which the head number (cylinder number) is 
determined as a result of appropriately counting the servo clock, the head 
number region 67c (cylinder number region 67d) in the servo information 
shown in FIG. 13 may be omitted accordingly. 
FIGS. 15A, 15B, 15C, 15D, 15E and 15F illustrate the head number 
determination in the third embodiment. FIGS. 15A through 15F show a case 
where heads HD0 and HD1 are used for reading the servo information 
67.sub.1 shown in FIGS. 15A and 15B previously written on the relevant 
magnetic disk recording surfaces. The counter 71 starts counting the servo 
clock pulses shown in FIG. 15C after the index signal is input (that is, 
after the true index is reached). The resulting count numbers of the 
counter 71 are shown in FIG. 15D. The count numbers are sent to the latch 
circuit 72 in series which holds one of the count numbers when the servo 
mark signal in the servo information 67.sub.1 is input. The held count 
number is supplied to the head number determining circuit 73. 
The head number determining circuit 73, using the head number table 74 
shown in FIG. 16, compares the supplied count number with determining 
position numbers in the head number table 74. The head number table 74 
includes the determining position numbers 2, 6, . . . , m which indicate 
the count numbers relevant to head numbers 0, 1, 2, . . . , n of the heads 
HD0, HD1, HD2, . . . , HDn. Therefore, the head number determining circuit 
73 determines that the servo information currently being read is 
information which is read through the head HD0 when the supplied count 
number is "2" as shown in FIG. 15E. Similarly, the head number determining 
circuit 73 determines that the servo information currently being read is 
information which is read through the head HD1 when the supplied count 
number is "6" as shown in FIG. 15F. 
Thus, the determination of a head, through which the servo information is 
being currently read, can be achieved without requiring the head number 
region 67c to be included in the servo information 67. As a result, it is 
possible to reduce an information amount required for the servo 
information 67, and thus to improve performance of the magnetic disk 
apparatus. 
A magnetic disk apparatus in a fourth embodiment will now be described. 
FIG. 17A shows a general arrangement of data-area servo information 
75.sub.1 through 75.sub.n written on a recording surface of magnetic disks 
31a. As shown in the figure, n items of the data-area servo information 
75.sub.1 through 75.sub.n are written in each of n+1 cylinders CYL0 
through CYLn. (It is noted that using the same symbol `n` for representing 
the numbers does not mean that there should be a specific relationship 
between the number of the magnetic heads, the number of the items of the 
servo information, the number of the items of the data-area servo 
information, and the number of the cylinders.) The n+1 cylinders are 
concentrically arranged in the magnetic disks 31a. As shown in FIG. 17A, 
each item of the n items of the data-area servo information 75.sub.1 
through 75.sub.n is written radially in a staggered manner. In other 
words, as shown in FIG. 17B, each item of the n items of the data-area 
servo information 75.sub.1 through 75.sub.n is written in the staggered 
manner for all the cylinders CYL0 through CYLn within a servo frame 
interval. 
The magnetic disk apparatus in the fourth embodiment includes a similar 
construction to that of the third embodiment shown in FIG. 14. In the 
fourth embodiment, a cylinder number determining circuit 73 is provided 
instead of the head number determining circuit 73. Cylinder numbers 0 
through n of the cylinders CYL0 through CYLn are determined by the 
cylinder number determining circuit 73. A cylinder number table 76 (see 
FIG. 19) is provided with the cylinder number determining circuit 73. In 
this embodiment, the cylinder numbers are determined by the cylinder 
number determining circuit 73. Therefore, the cylinder number region 67d 
in the servo information shown in FIG. 13 may be omitted. 
FIGS. 18A, 18B, 18C, 18D, 18E and 18F illustrate the cylinder number 
determination in the fourth embodiment. FIGS. 18A through 18F show a case 
where the servo information 75.sub.1 is read from cylinders CYL0 and CYL1 
in which, as shown in FIGS. 18A and 18B, the servo information 75.sub.1 
was previously written. The counter 71 starts counting the servo clock 
pulses shown in FIG. 18C after the index signal is input (that is, after 
the true index is reached). The resulting count numbers of the counter 71 
are shown in FIG. 18D. The count numbers are sent in series to the latch 
circuit 72 which holds one of the count numbers when the servo mark signal 
in the servo information 75.sub.1 is input. The held count number is 
supplied to the cylinder number determining circuit 73. 
The cylinder number determining circuit 73, using the cylinder number table 
76 shown in FIG. 19, compares the supplied count number with determining 
position numbers in the cylinder number table 76. The cylinder number 
table 76 includes the determining position numbers 2, 6, . . . , m which 
indicate the count numbers relevant to cylinder numbers 0, 1, 2, . . . , n 
of the cylinders CYL0, CYL1, CYL2, . . . , CYLn. Therefore, the cylinder 
number determining circuit 73 determines that the servo information 
currently being read is information which is read from the cylinder CYL0 
when the supplied count number is "2" as shown in FIG. 18E. Similarly, the 
cylinder number determining circuit 73 determines that the servo 
information currently being read is information which is read from the 
cylinder CYL1 when the supplied count number is "6" as shown in FIG. 18F. 
Thus, the determination of a cylinder, from which the servo information is 
currently being read, can be achieved without requiring the cylinder 
number region 67d to be included in the servo information 67. As a result, 
it is possible to reduce an information amount required for the servo 
information 67, and thus to improve performance of the magnetic disk 
apparatus. 
In each of the above-described third and fourth embodiments, the 
determination of the head number and cylinder number is not limited to 
that using the tables 74 and 76. It is also possible to determine them by 
appropriately calculating using the count number. 
Further, the determination of the head number and cylinder number is not 
limited to that counting after the index signal is input (that is, after 
the true index is reached). It is also possible to determine the head 
number and cylinder number as a result of measuring the time required for 
reaching another objective item of servo information. For example, in a 
case where items of servo information are written in a time interval of 
`T` and the servo frame interval is `a`, if a time of T+a is required for 
reaching another objective item of servo information, it can be determined 
that the head number (cylinder number) is incremented. Thus, it is 
possible to determine the head number and cylinder number. 
FIG. 20 shows a servo information arrangement written in the cylinders of 
magnetic disks for illustrating a variant of the above-described fourth 
embodiment of the present invention. In this arrangement, 5 cylinders CYL0 
through CYL4 are predetermined to belong to a block 1, and 5 cylinders 
CYL5 through CYL9 are predetermined to belong to a block 2. For the block 
1, as shown in FIG. 20, items of the servo information 75.sub.1, 75.sub.2, 
75.sub.3, . . . are recorded in a staggered manner. Similarly, for the 
block 2, as shown in the figure, items of the servo information 75.sub.m, 
75.sub.m+1, 75.sub.m+2, . . . are recorded in a staggered manner. 
If the magnetic disks have a large number of cylinders, considerable time 
is required for reaching the last cylinder CYLn after the index signal is 
input (the true index is reached). As a result, formatting efficiency may 
be degraded. In the variant of the fourth embodiment, items of servo 
information are arranged as shown in FIG. 20 so as to divide a number of 
the items of servo information into several blocks, and to manage each 
block of items of servo information individually. As a result, it is 
possible to reduce the time required for reaching a relevant data-area 
servo position. 
Some of the above-described embodiments are recording/reproducing 
apparatuses using the above-described data-area servo method. However, 
applications of the present invention are not limited to apparatuses using 
the data-area servo method. The present invention may also be applied to 
recording/reproducing apparatuses using the above-described servo-area 
servo method. Further, the present invention may also be applied to 
recording/reproducing apparatuses, each of which has a capability of using 
both the data-area servo method and servo-area servo method. 
Further, the present invention is not limited to the above-described 
embodiments, and variations and modifications may be made without 
departing from the scope of the present invention.