Method, apparatus, and medium for recording information in data sections having number of bytes which increases with increase in circumference of tracks on medium

An information recording and reproducing method and apparatus with increased recording density of an information recording medium using the sample servo method driven with a fixed angular velocity from the innermost circumference to the outmost circumference. A disk-shaped recording medium is concentrically divided into a plurality of areas. Recording is performed with a recording density suited for the radial position of each of the areas. The width of the areas is set so that the recording capacity of a user data section sandwiched between servo sections forming a segment may increase with every transition to an outer adjacent area while taking one byte as a unit. The recording and reproducing apparatus has a clock generating circuit for servo data extraction and a clock generating circuit for user data extraction. The latter clock generating circuit is synchronized by a synchronizing pulse generated by the former clock generating circuit.

BACKGROUND OF THE INVENTION 
The present invention relates to an information recording medium, an 
information recording and reproducing method, and an information recording 
and reproducing apparatus, and in particular to an information recording 
medium, an information recording and reproducing method, and an 
information recording and reproducing apparatus suitable for optical disks 
and optical disk drive apparatuses using the sample servo method. 
Conventionally, in optical disk apparatuses, the tracking method has been 
frequently used. In the tracking method, a groove is provided on a disk 
and control is exercised so that an optical beam may be positioned on this 
groove. In this case, a control error signal is continuously obtained by 
detecting light diffracted by the groove from reflected light of the 
optical beam, and this method is called the continuous servo method. This 
continuous servo method has a problem that a difference in shape and 
reflectance between grooves affects the control error signal and worsens 
the tracking precision. At the time of recording, an optical beam having a 
larger quantity of light than that at the time of reading is incident and 
hence the quantity of reflected light is increased in proportion to the 
quantity of incident light. This necessitates such a contrivance as to 
obtain a proper control error signal. 
In the sample servo method, however, a sample servo format is used instead 
of the groove as means for obtaining the control error signal, a servo 
section and a data section are alternately disposed on tracks of a disk, 
and control is so exercised that an optical beam may be passed over the 
servo section. As for the control error signal, one set of tracking pits 
(two tracking pits) disposed so as to be offset around the track position 
in directions which are opposite to each other are recorded beforehand in 
the servo section. By detecting the difference between quantities of light 
reflected by the disk when the optical beam passes through both pits, the 
control error signal is obtained. In the sample servo system, therefore, 
there is no influence due to the groove because there is no groove. 
Further, the control error signal is derived only from the servo section, 
and only the operation for obtaining servo information is conducted in 
this area. Therefore, the influence due to the increase of the quantity of 
laser light at the time of recording is avoided. Some problems of the 
continuous servo method are thereby solved. 
On the other hand, information recording and reproducing apparatuses such 
as optical disks and magnetic disks are demanded to have larger capacities 
with an increase in quantity of information to be dealt with. For this 
purpose, the recording density on disks must be increased. In the 
so-called CAV (Constant Angular Velocity) method of conducting a 
recording/reproducing operation while rotating a disk at a constant 
angular velocity, the space between pits (pit period) is limited at the 
innermost circumference where the linear velocity becomes the slowest. 
Therefore, the out the circumference is located, the larger is the 
allowance between pits. In a circumference having a diameter which is 
twice that of the innermost circumference, for example, the recording 
density is decreased to 1/2. Thus, in the CAV method, the recording 
capability of the disk is not used sufficiently, resulting in waste. 
In contrast, the CLV (Constant Linear Velocity) method of keeping the 
linear velocity constant produces the same recording density from inner 
circumferences to outer circumferences and hence provides the maximum 
recording capacity. In the CLV method, however, the angular rotational 
velocity of the disk must be changed according to the track position in 
order to keep the linear velocity constant and hence the access time 
becomes longer than that of the CAV method. This hinders its use as a 
computer memory, of which high-speed access performance is required. As 
one of methods aiming at eliminating drawbacks of both methods, therefore, 
an apparatus in which a disk is divided into a plurality of areas in the 
radial direction and different angular velocities are set for respective 
areas so as to increase the recording density, is described in 
JP-A-61-172223. Further, an apparatus in which a disk is divided into a 
plurality of areas in the same way and the recording density is increased 
by changing the pit period in each area while keeping the angular velocity 
constant is described in JP-A-61-175968. However, neither of them makes 
mention of the tracking method. 
Further, as an example of an apparatus for dividing a disk into a plurality 
of areas in the radial direction and conducting a recording/reproducing 
operation in the same way, JP-A-1-128276 can be mentioned. This relates to 
an optical disk apparatus using the sample servo method. Over the entire 
face of the disk, the sample period of servo information is not changed 
but is fixed. Only the frequency of the data section in each of a 
plurality of divided areas is changed so as to increase the recording 
density of each area. Reference may further be made to JP-A-1-204272, 
JP-A-2-162578, JP-A-2-260285 and JP-A-3-187072 published on Aug. 15, 1991. 
SUMMARY OF THE INVENTION 
In the sample servo method, it is necessary to derive servo information 
from the servo section at a fixed period as described before. Therefore, a 
higher density cannot be attained by using the method of arbitrarily 
setting areas and changing the speed of rotation or changing the recording 
clock period as in the above described prior art intended for the 
continuous servo method. Especially, consideration must be given to 
generation of the clock for obtaining servo information which should be 
constant over the entire face of the disk and the recording/generating 
clock which changes according to the radius. Consideration must also be 
given to the fact that the data section is divided by the servo section. 
Therefore, an object of the present invention is to solve the above 
described problems of the prior art and provide an improved information 
recording medium, an information recording and reproducing method, and an 
information recording and reproducing apparatus capable of attaining a 
higher density and increasing the recording capacity while making the most 
of the characteristics of the sample servo method. 
In an information recording and reproducing apparatus according to the 
present invention, a servo section is disposed on an optical disk medium 
at fixed angular intervals so that servo information may be obtained from 
the disk, which rotates at constant angular velocity, at fixed periods. 
The optical disk medium is divided into a plurality of bands in the radial 
direction. The information recording and reproducing apparatus includes a 
servo clock generating circuit for generating a clock which is used to 
obtain servo information and which is identical over the entire face of 
the disk, a data clock generating circuit for generating a clock which is 
used to record/reproduce data and which differs from band to band, and a 
sector detection circuit for detecting sectors, which are different in 
data capacity and the number per circumference from band to band. 
With the clock obtained by the servo clock generating circuit, reproduction 
of the servo area and position control of the optical pickup are 
conducted. In order to increase the recording density of each band, the 
data clock generating circuit generates a clock having a period which 
becomes shorter as the band is located on the side of an outer 
circumference of the optical disk medium. The data recording period is so 
chosen as to have an integer ratio with respect to the period of the servo 
section. Partitions between bands are formed so that the capacity of a 
data area sandwiched between servo areas may increase for each transition 
to an adjacent outer band while taking a predetermined fixed number of 
bytes as the unit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
&lt;Embodiment 1&gt; 
By referring to FIGS. 1 to 10, examples of application of an information 
recording medium of the present invention, its recording and reproducing 
method, and an information recording and reproducing apparatus for driving 
it to an optical magnetic disc and an optical magnetic disk drive 
apparatus will now be described. 
(1) Examples of Configuration of Information Recording and Reproducing 
Apparatus 
FIG. 1 is a block diagram showing an example of an optical magnetic disk 
drive apparatus functioning as an information recording and reproducing 
apparatus of the present invention. By referring to FIG. 1, the outline of 
the apparatus configuration will now be described. In FIG. 1, portions 
having no direct relations to the present invention are not illustrated. 
Numeral 1 denotes an optical disk functioning as an information recording 
medium of the present invention which will be described later in detail. 
Numeral 2 denotes a spindle motor for rotating the disk 1 with a constant 
angular velocity. Numeral 3 denotes an optical pickup, 4 a magnetic head 
for generating a magnetic field at the time of recording or erasing, 5 a 
preamplifier, 6 an A/D converter for converting a prepit signal to a 
digital signal, 7 an A/D converter for converting an optical magnetic 
signal reproduced by an optical magnetic effect to a digital signal, 8 a 
servo information detection circuit, 9 a clock pit detection circuit, 10 a 
servo clock generating circuit, 11 a data clock generating circuit, 12 a 
modulation circuit, and 13 a demodulation circuit. Further, numeral 14 
denotes modulated data to be recorded, 15 reproduced prepit data, 16 a 
reproduction signal obtained by the optical magnetic effect, 17 a clock 
pit detection signal, 18 a servo clock, 19 a data clock, and 31 a servo 
information detection timing signal. 
(2) Examples of Information Recording Medium 
As an example of a format of the sample servo method, FIG. 2 shows a DBF 
(Discrete Block Format) scheme proposed in ISO standards (ISO/IEC JTC1 
Information Technology--90 mm Rewritable Optical Disk Cartridge, 
JTC1/SC23/WG2 1st DP10090). 
In the sample servo method, the disk face is divided into servo areas and 
data areas in the track direction as shown in FIG. 2. In the track 
scanning direction, the servo areas and the data areas are alternately 
disposed. When they are viewed on the disk face, the servo areas are 
arranged so as to form straight lines in the radial direction of the disk 
at intervals of fixed angles. A servo area includes six prepits. The first 
three pits are pits for obtaining a track crossing signal in the seek 
operation and they are called access. The last three pits are servo pits. 
Among the servo pits, two pits are disposed so as to be offset on both 
sides of the track center. A central pit is recorded on the track center. 
The offset pits are called wobble pits. By controlling positions of the 
optical pickup so that quantities of light reflected by the wobble pits 
become equal, tracking onto the track is made possible. The central pit is 
called a clock pit and it is used as a reference signal for clock 
generation. In addition, a mirror section having no pits recorded therein 
is set in the last portion of the servo area. A focus error signal can be 
derived from the mirror section. A combination of the mirror section and a 
sector mark which will be described later forms a unique pattern for 
detecting the servo area. By such a format, an operation for obtaining a 
servo signal and an operation for recording and reproducing data can be 
separated temporally. As compared with the continuous servo method whereby 
a groove is provided and traced, therefore, a more stable optical disk and 
drive apparatus can be realized. 
An example in which the present invention has been applied to the optical 
disk of this sample servo method is shown in FIG. 3. FIG. 3 shows an 
example in which a recording and reproducing area is divided into six 
portions A to F in the radial direction of the disk. In general, the 
larger the number of divisions becomes, the larger capacity can be 
obtained. As described later, however, there is a limit in implementation. 
In FIG. 3, bands are defined by definite partition lines. However, they 
are shown only for the purpose of explanation. Virtual partition lines may 
be used because there are no tracking grooves in fact. 
FIG. 4 shows an expanded view of a boundary portion between bands A and B. 
In the band A located on the innermost circumference side, data of 8 bytes 
are recorded in the data area. In the adjacent band B located on the outer 
circumference side, however, data of 9 bytes are recorded. By narrowing 
the width of the band to half of that of FIG. 3, for example, it is also 
possible to record data of 8.5 bytes. In case a group code taking 1 byte 
as the unit is used as the recording modulation code, however, a data 
space of 0.5 byte cannot be used. Therefore, it is efficient to set bands 
so that the quantity of data may increase while taking one byte as the 
unit. In the same way, data of 10, 11, 12 and 13 bytes are recorded in 
other bands C to F of the disk shown in FIG. 3, respectively. 
An area having a combination of a servo area and a data area is referred to 
as segment. A collection of a plurality of segments forms a sector. An 
actual data recording/reproducing operation is conducted by taking a 
sector as the unit. FIG. 5 shows an example of a configuration of a 
sector. In FIG. 5, the length of a sector in each band is represented by 
the number of segments in use. The further out the band is located, the 
larger number of data can be recorded in each segment and hence the 
smaller number of segments form each sector. At the head of a sector, a 
sector mark (SM) 51 is disposed. Subsequently, as ID information 52, 
position information such as a track number and a sector number and other 
accompanying information are recorded. Subsequently, user data 53 to be 
used directly by the user and an error correction code (ECC) 54 for 
performing error correction at the time of reproduction are recorded. As 
the user data 53, a power of 2 such as 512 bytes or 1024 bytes is 
typically set. In the example of FIG. 5, 2 bytes for the sector mark, 22 
bytes for the ID information, 512 bytes for the user data, and 72 bytes 
for the ECC form each sector. That is to say, 608 bytes in total form each 
sector. 
In the disk 1 of FIG. 3, 1672 segments are disposed in each circumference 
of the disk. In the band A, each track is divided into 22 sectors and each 
sector is formed by 76 segments. Therefore, a surplus area is not 
generated. 
In the band B, data of 9 bytes are recorded in the data area included in 
each segment. Therefore, each track is divided into 24 sectors and each 
sector is formed by 69 segments. In this case, each sector has a capacity 
of 621 bytes. However, the required capacity is 608 bytes and remaining 13 
bytes (surplus area 55) are not used. Further, in this band, a surplus of 
16 segments is generated every track. In the same way, other bands also 
have the configuration as shown in Table 1. 
TABLE 1 
______________________________________ 
First example of division 
The number 
The number of sectors 
Band of tracks per track Capacity [MByte] 
______________________________________ 
A 2000 22 22 
B 2000 24 24 
C 2000 27 27 
D 2000 29 29 
E 2000 32 32 
F 667 35 11.7 
Total 145.7 
CAV capacity 117.3 
MCAV/CAV 1.24 
______________________________________ 
Capacity = (The number of tracks) .times. (The number of sectors per 
track) .times. (User data quantity of 512 bytes) 
It is assumed in Table 1 that the recording area in the radial direction of 
the disk of 3.5 inch is 24-40 mm and the track pitch is 1.5 .mu.m. A 
recording capacity equivalent to 1.24 times as large as that of a 
conventional CAV disk (i.e., the case where the number of sectors per 
track is 22 in every band) is obtained. 
As another example, in a case where each segment has a servo area of 2 
bytes and a data area of 16 bytes and one circumference of the disk has 
1672 segments under a similar condition, a capacity equivalent to 1.27 
times is obtained as shown in Table 2. 
TABLE 2 
______________________________________ 
Second example of division 
The number 
The number of sectors 
Band of tracks per track Capacity [MByte] 
______________________________________ 
A 1000 44 22 
B 1000 46 23 
C 1000 49 24.5 
D 1000 52 26 
E 1000 53 26.5 
F 1000 57 28.5 
G 1000 59 29.5 
H 1000 61 30.5 
I 1000 64 32 
J 1000 69 33 
K 667 23.0 
Total 298.5 
CAV capacity 234.7 
MCAV/CAV 1.27 
______________________________________ 
As another example, FIG. 6 shows a recording medium on which head positions 
of sectors including one sector of every track are aligned in the radial 
direction. For finding out the head of a sector, it is necessary to detect 
a sector mark (SM) first of all. As the sector mark, a pattern which does 
not appear in other data is typically used. In actual reproduction of a 
disk, however, the same pattern as the sector mark is detected in some 
cases due to a stain or defect. In an adopted technique, therefore, a 
detection window exploiting a past record is generated and only a sector 
mark detection signal which has appeared in this detection window is 
adopted as a correct one. For obtaining a correct detection window, 
however, a pull-in time of a certain degree is required to obtain a 
correct detection window. In the above described recording medium, 
however, the sector period differs from band to band. In a case where a 
seek operation has been conducted beyond a boundary between bands, 
therefore, a sector mark detection operation must be conducted from the 
initial state. In the present example, sector marks are located at the 
same position at the rate of one location per circumference. Therefore, 
the detection window for this sector mark can be used in common to all 
bands. By using the sector mark detected by this detection window as a 
standard, sector mark detection according to the period of each band can 
be immediately performed. As a result, the pull-in time can be shortened. 
As a matter of course, the presence of sector marks in a larger number of 
common positions enhances the stability of the detection window and 
provides a better result. However, it is important to dispose sector marks 
in at least one common position. 
Another embodiment of an information recording medium is shown in FIG. 7. 
In this example, the sector mark 51 and the ID 52 disposed at the head of 
each sector are recorded with the same recording density as that of the 
servo area at all times. Therefore, the same number of segments are 
occupied at all times. Also, in a case where a seek operation is conducted 
beyond a boundary between bands, the track number and sector number 
contained in ID 52 can be immediately read without switching the clock, 
resulting in an effect of shortened seek time. However, the recording 
capacity is somewhat lowered. As compared with the example shown in Table 
1, the capacity becomes 145.3 MBytes, which is 1.24 times that of the CAV 
method. 
By referring to FIGS. 3 to 7, examples of an information recording medium 
have heretofore been described. In the following section (3), an operation 
for actually driving optical magnetic disks illustrated in FIGS. 3 to 7 by 
using the information recording and reproducing apparatus shown in FIG. 1, 
i.e., a recording and reproducing method, will be described. 
(3) Description of Operation of Information Recording and Reproducing 
Apparatus (Information Recording and Reproducing Method) 
The optical disk 1 illustrated in FIG. 1 is rotated at a constant angular 
velocity by a spindle motor 2. The optical pickup 3 has a well-known 
configuration and includes a laser diode, a photo-detector, optical 
components and servo mechanism components. As a matter of fact, a linear 
motor for seek operation and so on are also added. Since they do not 
directly relate to the present invention, however, they are not 
illustrated. The output of the optical pickup 3 is amplified and separated 
into a prepit reproduction signal 15 and an optical magnetic reproduction 
signal 16 by the preamplifier 5. The prepit reproduction signal 15 is 
supplied to the succeeding A/D converter 6 and clock pit detection circuit 
9. The optical magnetic reproduction signal 16 is supplied to the A/D 
converter 7. On the basis of the above described unique pattern of the 
prepit reproduction signal 15, the clock pit detection circuit 9 first 
discriminates the servo area and the data area, and then extracts the 
above described clock pit. The clock pit detection signal 17 is inputted 
to the servo clock generating circuit 10 and the data clock generating 
circuit 11. Clock generating is thus performed. The servo clock generating 
circuit 10 and the data clock generating circuit 11 are formed by a 
so-called phase-locked loop (PLL) and generate clocks synchronized in 
phase to the clock pits. 
As shown in FIG. 8, the servo clock generating circuit 10 is formed by a 
phase comparator 81, a low-pass filter 82, a voltage-controlled oscillator 
83, and a frequency counter 84. The servo clock generating circuit 10 
further includes a decoder 85, which generates a synchronizing pulse 20 
for synchronization with the data clock generating circuit 11, and a 
decoder 86, which generates a timing signal 31 for detecting servo 
information. The sample servo format of the present example has a ratio of 
8 bytes to 2 bytes as a ratio of data area to servo area. In this method, 
data of one byte are converted into 11 channel bits and recorded. 
Therefore, the frequency counter 84 is so set as to have a frequency 
counter divisor of 1/110. It is a matter of course that if a different 
format is used, the frequency counter divisor should be changed according 
to it. The servo clock 18 thus generated serves as a conversion clock of 
the A/D converter 6. The servo clock 18 is further used to extract servo 
information in the servo information detection circuit 8. 
As shown in FIG. 9, the data clock generating circuit 11 also has a PLL 
circuit formed by a phase comparator 91, a low-pass filter 92, a 
voltage-controlled oscillator 93, and a first frequency counter 94. The 
data clock generating circuit 11 further includes a second frequency 
counter 95 for exercising frequency dividing of the output of the 
voltage-controlled oscillator 93 to generate the data clock 19. The second 
frequency counter 95 is reset by the above described synchronization pulse 
20 to be synchronized to the servo clock 18. From band to band of the 
disk, the frequency counter divisor of the first frequency counter 94 is 
switched by a switching signal 24 supplied from a controller which is not 
illustrated. Table 3 shows relations between bands and frequency counter 
divisors. 
TABLE 3 
______________________________________ 
Frequency counter divisor 
in first example of division 
Data First 
quantity First Second 
ratio/second 
Band (Byte) ratio ratio ratio 
______________________________________ 
A 8 440 4 110 
B 9 495 4 123.75 
C 10 550 4 137.5 
D 11 605 4 151.25 
E 12 660 4 165 
F 13 715 4 178.75 
______________________________________ 
By taking 8 bytes as a standard, the length of the data area on the disk 1 
becomes 1.125 times for 9 bytes, 1.25 times for 10 bytes, . . . , 1.625 
times for 13 bytes. Therefore, it is necessary to raise the frequency of 
the clock as well in the same way. Since the frequency counter divisor of 
the PLL must be an integer, however, values such as 123.75, 137.5, . . . , 
178.75 cannot be used. By generating a clock having a frequency which is 
four times as large as the original frequency as shown in FIG. 9, all 
frequency counter divisors become integers and hence the PLL can be 
formed. However, the phase of the data clock after frequency division with 
a ratio of 4 to 1 at the head of the data area does not become constant. 
Therefore, phasing is performed by means of the synchronizing pulse 20 
generated by the above described servo clock generating circuit 10. FIG. 
10 shows a timing chart of this operation (a timing chart of clock 
synchronizing timing). 
Every first frequency counter divisor shown in Table 3 includes 11 as its 
factor. This indicates that in a case where the recording modulation code 
is not the code of the present example in which one byte is converted to 
11 channel bits, such as in case one byte is recorded as 8 channel bits, 
the present invention can be applied by changing the frequency counter 
divisor from 11 to 8 on the basis a similar way of thinking. 
For a disk having the configuration shown in Table 2, the frequency counter 
divisor in the servo clock generating circuit 10 is similarly set at 198 
and the frequency counter divisors in the data clock generating circuit 11 
is set at a value shown in Table 4. That is to say, the ratio of data area 
to servo area is 16 bytes to 2 bytes, and one byte is converted to 11 
channel bits and recorded in this method. Therefore, the frequency counter 
84 is so set as to have a frequency counter divisor of 1/198. 
TABLE 4 
______________________________________ 
Frequency counter divisor 
in second example of division 
Data First 
quantity First Second 
ratio/second 
Band (Byte) ratio ratio ratio 
______________________________________ 
A 16 1584 8 198 
B 17 1683 8 210.75 
C 18 1782 8 222.75 
D 19 1881 8 235.125 
E 20 1980 8 247.5 
F 21 2079 8 259.875 
G 22 2178 8 272.25 
H 23 2277 8 284.625 
I 24 2376 8 297 
J 25 2475 8 309.375 
K 26 2574 8 321.75 
______________________________________ 
&lt;Embodiment 2&gt; 
As another example of an information recording and reproducing apparatus, 
the block diagram of an apparatus for performing phasing of the above 
described data clock by using a specific pattern included in recorded data 
is shown in FIG. 11. In FIG. 11, the present invention has been applied to 
an optical magnetic disk drive apparatus in the same way as FIG. 1. The 
same components are denoted by like numerals. In FIG. 11, a pattern 
detection circuit 22 and a switching circuit 23 are newly added. This 
pattern detection circuit 22 detects a specific pattern out of the 
reproduction signal. The second frequency counter 95 included in the data 
clock generating circuit 11 of FIG. 9 is reset by this detection signal. 
This specific pattern is recorded at the head of user data of the segment 
simultaneously with data recording. 
FIG. 12 shows an example of the pattern detection circuit. The reproduction 
signal 16 is subjected to binarization in a comparator 121 and sampled 
into a shift register 122 by a clock 96 outputted from a VCO 
(voltage-controlled oscillator) included in the data clock generating 
circuit 11, i.e., a clock having a frequency which is four times as large 
as the frequency of the channel bit clock. The signal thus sampled 
undergoes pattern detection in a decision circuit 123. A resultant pattern 
detection signal 124 resets the second frequency counter 95 included in 
the second clock generating circuit. Thereby, phase synchronization 
between reproduction data and clock is performed as shown in FIG. 13. That 
is to say, FIG. 13 shows a timing chart of clock synchronizing timing. In 
accordance with a selection signal supplied from a controller (not 
illustrated), the switching circuit 23 of FIG. 11 selects the 
synchronizing pulse 20 supplied from the servo clock generating circuit 10 
or the pattern detection signal 124 supplied from the pattern detection 
circuit 22. The signal thus selected is supplied to the data clock 
generating circuit 11. Only when data already recorded is to be read is, 
the pattern detection signal 124 selected. In other states, the 
synchronizing pulse 20 is selected. 
&lt;Embodiment 3&gt; 
An example of an information recording and reproducing apparatus 
corresponding to the recording medium described by referring to FIG. 7 is 
shown in a block diagram of FIG. 14. Description will now be given by 
referring to FIG. 14. In FIG. 14, an output 29 of the first A/D converter 
6 or an output 30 of the second A/D converter 7 is selected and supplied 
to the demodulation circuit 13 as input data by a selection circuit 26. As 
for the clock used in the demodulation circuit 13, the servo clock 18 or 
the data clock 19 is selected by a selection circuit 27 and supplied to 
the demodulation circuit 13. The selection circuit 26 selects the first 
A/D converter 6 at the time of reproduction of ID information and selects 
the second A/D converter 7 at the time of reproduction of other data. The 
selection circuit 27 selects the servo clock 18 at the time of 
reproduction of ID information and selects the data clock 19 at the time 
of reproduction of other data. Both selection circuits 26 and 27 are 
controlled by a selection signal 28 supplied from a controller (not 
illustrated). 
&lt;Embodiment 4&gt; 
A format of a medium facilitating phasing of the servo clock to the data 
clock and an information recording and reproducing method and an 
information recording and reproducing apparatus using this medium will now 
be described. 
FIG. 15 shows a new example of a segment configuration of a recording 
medium. As shown in FIG. 16, this medium also takes the shape of a disk in 
the same way as the above described examples. The medium is divided into a 
plurality of bands in the radial direction and rotated at a constant 
angular velocity. The disk face is divided into five bands A to E. In the 
innermost band A, each segment is divided into 11 equal parts to form a 
servo area occupying 3 bytes and a data area occupying 8 bytes. Servo 
areas are arranged in the radial direction of the disk so as to form a 
straight line. Therefore, the further out the segment is located, the 
longer the segment length becomes and the more data can be recorded. In 
any band, however, the temporal lengths of the servo area and the data 
area are constant and proportions of them to the segment length on the 
disk are always constant. Positions of clock pits also form a straight 
line in the radial direction of the disk. By using the clock pit as a 
reference signal of clock generation, servo clocks dividing the space 
between clock pits, i.e., one segment, into integer equal parts are 
generated. Detection of servo information such as detection of wobble pits 
is performed. A recording and reproducing operation of the data area is 
also conducted with the data clock generated by using the clock pit as a 
standard. In the innermost band A, this data clock has the same frequency 
as that of the servo clock. However, the further out the band is located, 
the higher the frequency of the data clock becomes. In the example of FIG. 
15, the recording method is decided to be NRZ (Non Return to Zero). 
Therefore, the number of channel bits is equal to the number of data bits, 
and it is 8 bits per byte. Therefore, the frequency counter divisor 
between the clock pit period and the servo clock period is 8.times.11=88. 
The frequency counter divisor between the clock pit period and the data 
clock period in the innermost band is also 8.times.11=88. As for the 
frequency counter divisor between the clock pit period and the data clock 
period in any other band, a positive integer dividing the data area into 
equal parts and dividing the servo area into equal parts is selected. 
Assuming now that the number of bytes recorded in the data area is 9 bytes 
in the band B adjacent to the innermost band (band A) of FIG. 16, 72 is 
used as the number of clocks of the data clock. Since the length of the 
servo area is 3/8 of that of the data area, 27 clocks are used. In the 
band B, therefore, the frequency counter divisor of the data clock becomes 
99. By similar way of thinking, data of 10 bytes are recorded and the 
frequency counter divisor becomes 110 in the band C. In the band D, data 
of 11 bytes are recorded and the frequency counter divisor becomes 121. In 
the outermost band E, data of 12 bytes are recorded and the frequency 
counter divisor becomes 132. In any band, the data area and the servo area 
are divided into equal parts by the data clock. In addition, the number of 
clocks in the data area is an integer times the number of channel bits per 
byte. In the boundary portion between the data area and the servo area, 
therefore, the phase of the servo clock coincides with the phase of the 
data clock. For the CAV method, it is now assumed that the number of bytes 
of the servo area is B.sub.S and the number of bytes of the data area is 
B.sub.D. For the MCAV method, it is now assumed that the number of bytes 
of the data area differing from band to band is B.sub.M and the number of 
channel bits is b.sub.c. Then the frequency counter divisor N is 
represented by the following equation. 
EQU N=[(B.sub.D +B.sub.S)/B.sub.D ].multidot.B.sub.M .multidot.b.sub.c(1) 
By deciding the frequency counter divisor N of the data clock so as to be 
the product of the reciprocal of the proportion of the data area length to 
the segment length, the number of bytes of the data area, and the number 
of channel bits and to be an integer, the phase of the data clock in the 
area boundary portion can be made constant. The number of data bytes BM 
increases or decreases from band to band while taking one byte as the 
minimum unit. The number of channel bits b.sub.c is decided by the 
recording modulation method. Both of them are integers. The proportion of 
the data area length to the segment length is represented by a value in 
the state in which the servo clock coincides with the data clock, i.e., a 
value obtained by dividing the number of bytes of the data area in the CAV 
method by the number of bytes of one segment. The number of data bytes 
B.sub.D and the number of servo bytes B.sub.S in the CAV method are also 
integers. If it is attempted to make the reciprocal of the proportion of 
the data area length to the segment length an integer in order to make the 
frequency counter divisor an integer, the proportion of the servo area 
length to the segment becomes large and the recording capacity is 
decreased. As an optimum method, setting is so made that a value obtained 
by dividing the product of the number of channel bits b.sub.c per byte and 
the total number of bytes (B.sub.D +B.sub.S) in the CAV method by the 
number of data bytes B.sub.D of the data area in the CAV method may become 
an integer. Alternatively, setting is so made that a value obtained by 
dividing the number of channel bits b.sub.c by the number of data bytes 
B.sub.D in the CAV method may become an integer. Thereby, an optimum 
frequency counter divisor of the data clock is realized in every band of 
the MCAV method. In the example of FIG. 15, the recording modulation 
method is NRZ and the number of channel bits is 8. Therefore, the above 
described condition is satisfied by setting 8 as the number of bytes of 
the data area in the innermost band A. 
FIG. 17 shows a new example of a format in the case where the number of 
channel bits is 8. In the innermost band, the data area occupies 16 bytes 
and the servo area occupies 4 bytes. The data area increases by one byte 
every adjacent band. The disk is divided into 14 bands. In the innermost 
band, i.e., in the CAV method, the total number of bytes in one segment is 
20 and the number of data bytes is 16. Therefore, the value obtained by 
dividing the number of channel bits by the number of data bytes becomes 1 
or less. However, the product of this value and the total number of bytes 
becomes an integer and the above described condition is satisfied. In any 
case, however, the phase of the servo clock coincides with the phase of 
the data clock at a timing of every two bytes of the servo clock. On the 
other hand, if the increment of the data area between adjacent bands is 2 
bytes and the number of divisions is 7, an arbitrary number of bytes of 
the servo area can be set and the phase of the servo clock can coincide 
with the phase of the data clock every byte of the servo clock. 
Another example of a segment configuration is shown in FIG. 18. In this 
case, a recording modulation method with each byte having 11 channel bits 
is adopted and the disk face is divided into a plurality of bands in the 
radial direction. In the same way as in the example of FIG. 15, the servo 
clock for performing reproduction of the servo area in the innermost band 
coincides with the data clock for performing recording and reproduction of 
the data area. The number of data bytes in the innermost band is set at 
11. Even if the number of data bytes is set at an arbitrary integer 
exceeding 11 in other bands, therefore, the frequency counter divisor 
becomes an integer. Such a data format that the phase of the data clock in 
the boundary portion is constant in every band is realized. Although the 
number of bytes in the servo area is set at 2, this value is arbitrary. 
Since the number 11 of channel bits included in each channel is a prime 
number, a value smaller than this cannot be used as the number of data 
bytes in the innermost circumference. However, the number of data bytes in 
the innermost circumference can be set at 22 which is twice 11. In this 
case, however, the sum of the number of servo bytes and the number of data 
bytes of the CAV method must be made a multiple of 2. Alternatively, the 
number of data bytes in other bands must be made such a value that a 
remainder is not generated when it is divided by 2. In the same way, in a 
case where the number of data bytes in the innermost band is set at 33 
which is three times 11, the sum of the number of servo bytes and the 
number of data bytes in the CAV method must be made equal to a multiple of 
3. Alternatively, the number of data bytes in other bands must be made 
such a value that a remainder is not generated when it is divided by 3. 
FIG. 19 shows an example in which a recording modulation method with each 
byte having 12 channel bits is adopted. This corresponds to a recording 
modulation method known as (1, 7) RLL code. In this example as well, the 
servo clock for performing reproduction of the servo area in the 
inner-most band have the same period as that of the data clock for 
performing recording and reproduction of the data area in the same way as 
the above described two examples. The present invention is not limited to 
the byte length of the servo area shown in FIG. 19, either. If the number 
of bytes of the data area in the innermost band is set at 12 bytes and the 
number of bytes of the servo area is set at 2 bytes, the frequency counter 
divisor of the servo clock and the data clock in the innermost band 
becomes 168. In the outer band adjacent to the innermost band, the 
frequency counter divisor becomes 195 by making the number of bytes of the 
data area equivalent to 13. In the intermediate circumference shown in 
FIG. 19, the frequency counter divisor becomes 225 by making the number of 
bytes of the data area equivalent to 15. In the outer circumference, the 
frequency counter divisor becomes 285 by making the number of bytes of the 
data area equivalent to 19. In any case, the frequency counter divisor 
becomes an integer. By thus setting the number of bytes of the data area 
in the innermost band at 12, the frequency counter divisor becomes an 
integer when the number of bytes of the data area in other bands is an 
arbitrary integer exceeding 12. Therefore, an arbitrary number of bytes 
can be set. Further, in this recording modulation method, the number of 
bytes of the data area in other bands can be set at an arbitrary integer 
value in the same way as the above described example by setting the number 
of bytes of the data area of the innermost band at 6 bytes. 
Any of the examples heretofore described has been realized by satisfying 
the condition that the ratio between the number of channel bits per byte 
and the number of bytes of the data area in the state that the servo clock 
coincides with the data clock should be an integer. Therefore, it is 
evident that the present invention is effective even in a case of a 
recording modulation method other than the foregoing ones, i.e., even in a 
case where the number of channel bits per byte is different from that of 
the examples heretofore described. Further, a value other than the number 
of bytes of the data area described before as examples is realized while 
bringing about a similar effect so long as the above described condition 
is satisfied. 
Examples of a configuration of an information recording and reproducing 
apparatus will now be described. FIG. 20 shows an example of a block 
configuration. Components having the same functions as those of FIGS. 1, 
11 and 14 are denoted by like numerals and description of them will be 
omitted. It is here assumed that the prepit signals include the servo 
signal of the servo area and ID information of each sector, and the ID 
information and servo information are always recorded by the same clock as 
that of the servo signal. In case the ID information is recorded and 
reproduced by the same clock as the optical magnetic signal, however, it 
is possible to use such a configuration that the prepit signal 15 and the 
optical magnetic signal 16 are switched to be selectively inputted to the 
second A/D converter 7. Further, it is possible to employ such a 
configuration that only a single A/D converter is used and the input clock 
and conversion clock are appropriately switched. Detection of the servo 
information is performed in the servo information detection circuit 8 by 
the servo clock 18 synchronized to the clock pit detection signal 17 as 
shown in FIG. 21. Generation of the servo clock 18 is performed by the 
servo clock generating circuit 10. FIG. 22 shows an example of the servo 
clock generating circuit. A PLL similar to that of FIG. 8 is shown in FIG. 
22. Components having the same functions as those of FIG. 8 are denoted by 
like numerals. A decoder 85' generates a byte synchronizing signal 33 on 
the basis of the output of the frequency counter 84 and outputs the byte 
synchronizing signal 33 at a fixed position between segments. The byte 
synchronizing signal 33 is a signal functioning as a standard in data 
clock generation which will be described later. At the rising edge or 
falling edge of this signal, the phase of the servo clock 18 coincides 
with the phase of the data clock 19. By performing the band division and 
segment configuration under the above described condition, a signal 
obtained by extracting the servo clock 18 at intervals of one byte becomes 
the byte synchronizing signal 33. Further, it is not always necessary to 
use all of the signals obtained by extracting the servo clock 18 at 
intervals of one byte. Subject to the condition that each segment is 
divided into equal parts, a signal extracted at intervals of an arbitrary 
number of bytes can be used. Its minimum value is 1. That is to say, a 
byte synchronizing signal 33' which appears at a rate of one per segment 
can be used. 
FIG. 23 shows an example of a configuration of the data clock generating 
circuit 11. In the same way as in FIG. 22, this example also has the 
configuration of a PLL. Numeral 101 denotes a phase comparator, 102 a 
low-pass filter, 103 a voltage-controlled oscillator, and 104 a frequency 
counter. The frequency counter 104 is a variable divisor frequency counter 
having a frequency counter divisor which is changed by the control signal 
24 supplied from a controller (not illustrated). The frequency counter 
divisor is changed from band to band, and a data clock 19 having a 
different frequency is outputted. As shown in FIG. 21, however, the clock 
having any frequency is synchronized in phase to the byte synchronizing 
signal 33 functioning as the reference signal. 
At the same time, the byte synchronizing signal 33 functions as a reference 
signal at the time of recording and reproduction. As shown in FIG. 21, the 
head bit position of the data area in every band coincides in phase with 
one signal of the byte synchronizing signal 33 generated repetitively in 
one segment. By extracting this byte synchronizing signal located at the 
head of the data area, therefore, the recording and reproducing reference 
signal 34 common to all bands is obtained. To be specific, the decoder 85' 
in the example of the servo clock generating circuit shown in FIG. 22 
generates the recording and reproducing reference signal 34 on the basis 
of the output of the frequency counter 84. 
Another example of the information recording and reproducing apparatus is 
shown in FIG. 24. In FIG. 24, the same components as those of FIG. 20 are 
denoted by like numerals and description of them will be omitted. An 
optical disk used in this apparatus is preformatted so that the clock pit 
signal may be located on the boundary between bytes as shown in FIG. 25. 
In the same way as in the foregoing example, the servo clock generating 
circuit 10 of FIG. 24 generates the servo clock 18 by using the clock pit 
detection signal 17 as the reference signal. Unlike the foregoing example, 
the data clock generating circuit 11 uses the clock pit detection signal 
17 as the reference signal. By preformatting so that the clock pit signal 
may be located on the head position of the byte, the clock pit detection 
signal 17 assumes the same timing as that of the byte synchronizing signal 
33 in the foregoing example. Thereby, the decoder 85' shown in FIG. 22 
becomes unnecessary in the servo clock generating circuit, and the data 
clock generating circuit functions as a circuit having characteristics 
independent of those of the servo clock generating circuit. Therefore, the 
data clock generating circuit is not affected by jitter and the like of 
the servo clock generating circuit, resulting in improved stability. 
Further, since both clock generating circuits simultaneously conduct a 
synchronizing operation at the start, the rise time is advantageously 
shortened. 
In the same way as in the foregoing embodiment, the recording and 
reproducing reference signal 34 in this embodiment can also be obtained by 
decoding the output of the frequency counter 84 included in the servo 
clock generating circuit 10. However, the recording and reproducing 
reference signal 34 may also be obtained by counting a predetermined 
number of pulses of the servo clock 18 from the position of the clock pit 
detection signal 17. Further, as another method, the recording and 
reproducing reference signal 34 may also be obtained by decoding the 
output of the frequency counter 104 included in the data clock generating 
circuit 11. In any method, a recording and reproducing reference signal of 
high precision can be obtained with a simple configuration. This brings 
about higher precision of the bit recording position on the disk and 
enhances the compatibility. Further, in not only the MCAV method but also 
the CAV or CLV method, in not only a disk-shaped medium but also a 
tape-like or card-shaped medium, and even in case where the recording 
density can be improved by future advances in a configuration technique 
such as a shorter laser wavelength or a shorter wavelength owing to a 
narrower gap, compatibility with conventional media and apparatuses can be 
maintained more easily, resulting in an advantage. 
&lt;Embodiment 5&gt; 
A format of a recording medium realizing a larger recording capacity as 
compared with the foregoing embodiment, and an information recording and 
reproducing method and an information recording and reproducing apparatus 
using this medium, will now be described. 
A new example of a recording medium according to the present invention is 
shown in FIG. 26. In FIG. 26, the abscissa represents time. As shown in 
FIG. 27, this medium also takes the shape of a disk and it is divided into 
a plurality of bands in the radial direction in the same way as in the 
foregoing example. Each segment is divided into a plurality of areas by 
taking a byte as the unit and the areas are distributed to a servo area 
and a data area. As the band is located on an outer circumference, the 
number of bytes in each segment becomes larger and the time length of each 
byte becomes shorter. In addition to the clock pit and wobble pits, the 
above described access marks, mirror section for focusing and unique 
pattern are also disposed as, occasion demands. Since the in positions and 
pattern exert no influence upon the present invention, however, they are 
not illustrated. The number of bytes of the servo area is constant 
irrespective of the band. Therefore, the time length of the servo area 
also becomes shorter as the band is located further out. However, the 
clock pit and the wobble pits are so arranged as to be aligned in the 
radial direction. The frequency of the clock for recording and detecting 
the servo signal may have an arbitrary value so long as it is an integer 
times as large as the repetition frequency of the clock pit. However, the 
time length of the servo area becomes shorter as the band is located 
further out. Therefore, the clock pit and wobble pits are arranged so that 
the shortest servo area may accommodate the servo signal. Further, 
relative arrangement of servo signals in the servo area is arbitrary. If 
positions of the servo signals are brought too close to each other, 
however, a reproducing optical beam reproduces a plurality of pits at the 
same time and correct detection cannot be performed. This phenomenon 
becomes more conspicuous as the band is located further in. Therefore, 
arrangement of pits and the number of bytes of the servo area are 
determined while paying regard to this point. FIG. 28 shows an example of 
a reproduced waveform. Since wobble pits are already recorded in the same 
temporal positions from the clock pit over the entire disk area, the 
wobble pits are always observed in the same positions of the reproduced 
waveform. In FIG. 28, it is assumed that the wobble pit signals are 
recorded at the recording and reproducing frequency of the data area in an 
outer band and they can be detected at the time of reproduction. As 
described before, however, the clock for detecting servo information is 
not limited to this. 
TABLE 5 
______________________________________ 
The The 
number number 
The of of 
number sectors bytes Frequency 
of per Capacity 
per counter 
Band tracks track [MByte] 
segment 
divisor 
______________________________________ 
A 1600 22 17.6 10 110 
B 1600 24 19.2 11 121 
C 1600 27 21.6 12 132 
D 1600 29 23.2 13 143 
E 1600 32 25.6 14 154 
F 1600 35 28.0 15 165 
G 1067 38 20.2 16 176 
Total 155.4 
CAV capacity 117.3 
MCAV/CAV 1.32 
______________________________________ 
Table 5 shows specific examples of numerical values. It is assumed that the 
number of clocks forming one byte is 11, and the number of clocks forming 
a servo area is 22, i.e., 2 bytes. It is further assumed that the shortest 
pit length is 0.8 .mu.m. The diameter of the innermost circumference is 24 
mm, and the diameter of the outermost circumference is 40 mm. The number 
of servo areas per circumference is 1672. The number of bytes per segment 
changes from 10 to 16. The frequency counter divisor changes from 110 to 
176. If a sector forming the unit of data recording and reproducing 
operation has 608 bytes (inclusive of 512 user bytes) and the track pitch 
is 1.5 .mu.m, then each of bands A to F has 1600 tracks and the band G has 
1067 tracks. As the user data capacity, the value of 155.4 MB is obtained. 
This is 1.32 times as large as the capacity (CAV capacity) obtained when 
the configuration of the band A is used over the entire disk. 
A recording medium using another new disk format will now be described. 
FIG. 29 is a segment configuration diagram showing the new disk format. In 
FIG. 29 as well, each segment is divided into a plurality of areas while 
taking a byte as the unit and the areas are distributed to a servo area 
and a data area in the same way as in FIG. 26. In addition, the disk is 
divided into 7 bands in the radial direction in the same way as in FIG. 
27. Each band also has the same configuration as that shown in Table 5. In 
the innermost band A, each segment is divided into 10 equal parts to form 
a servo area having 2 bytes and a data area having 8 bytes. As a band is 
located further out, the segment length becomes longer and hence more data 
can be recorded. In an intermediate band D, each segment is divided into 
13 equal parts to form a servo area having 2 bytes and a data area having 
11 bytes. In the outermost band G, each segment is divided into 16 equal 
parts to form a servo area having 2 bytes and a data area having 14 bytes. 
As for the configuration of the servo area, a clock pit and wobble pits 
are disposed in that order. Further, the above described access marks, 
mirror section for focusing and unique pattern are also disposed as 
occasion demands. Since the in positions and pattern exert no influence 
upon the present invention, however, they are not illustrated. The further 
out the band is located, the shorter the time length of the servo area 
becomes. In every band, positions of the clock pits are aligned so as to 
form a straight line in the radial direction of the disk. By using the 
clock pit as a standard, the position of a wobble pit is prescribed by the 
number of clocks from the clock pit. Since the clock period differs from 
band to band, positions of wobble pits align so as to form a straight line 
in the radial direction within each band, but they do not align between 
bands. 
FIG. 30 shows an example of a reproduced waveform. Wobble bits are set at 4 
clocks after the clock pit and 7 clocks after the clock bit. 
Representation on the time axis with the clock pit taken as a standard 
results in a reproduced waveform 15 in an inner band and an outer band. 
Band division is performed so that the number of bytes in each segment may 
become an integer and the shortest pit length in the innermost track of 
each band may become equivalent to the shortest pit length in the 
innermost track of the innermost band. The number of clocks in each 
segment, i.e., between clock pits, may have an arbitrary value so long as 
it is an integer. By making it equivalent to a multiple of the number of 
clocks forming one byte, however, use without waste becomes possible. 
Therefore, the number of band divisions changes depending upon the 
shortest pit length for a recording and reproducing operation, the number 
of clocks forming one byte, the number of clocks forming a servo area, the 
innermost diameter and the outermost diameter for a recording and 
reproducing operation, and the number of servo areas per circumference, 
for example. 
FIG. 31 shows a block diagram of an information recording and reproducing 
apparatus using the medium of FIG. 26. In FIG. 31, the present invention 
has been adopted in an optical magnetic disk drive apparatus. The same 
components as those of FIGS. 1, 11, 14 and 20 are denoted by like numerals 
and detailed description of them will be-omitted. The operation of the 
apparatus is controlled by a controller which is not illustrated. At the 
start, the motor 2 is rotated to drive the optical disk 1 with a constant 
angular velocity. Then, laser of the optical pickup 3 is energized to 
enable detection of reflected light of the prepit signal. The reflected 
light signal 15 amplified by the preamplifier 5 is inputted to the clock 
pit detection circuit 9 to detect a clock pit. FIG. 32 shows an example of 
configuration of the clock pit detection circuit 9. In FIG. 32, numeral 
191 denotes a peak detector for detecting the peak position of a clock 
pit, and numeral 192 denotes a unique pattern detector. Numerals 193 and 
194 respectively denote a detection window generator and a fixed 
oscillator. Numeral 195 denotes a gate for extracting only the peak signal 
in the detection window interval. Clock pit detection is started with 
detection of a unique pattern recorded with prepits functioning as the 
starting point. The unique pattern is disposed before or behind the servo 
information. However, it is not always necessary to dispose the unique 
pattern for every servo information. For example, the unique pattern may 
be disposed for each sector. Since a clock synchronized to the 
reproduction signal is not obtained at this time point, a pattern which 
can be detected by an asynchronous clock (such as continuation of "1" or 
"0" or repetition of a long period) must be used. Further, for making 
detection of this specific pattern possible no matter which position of 
the disk the optical pickup 3 is located in, such a pattern that it can be 
detected by the same clock in every band must be used. If the unique 
pattern is detected, a detection window for detecting a clock pit is 
generated by using the unique pattern as a standard and only the clock pit 
is extracted from the reproduction signal 15. Once a clock pit is 
detected, the next detection window is generated by using the clock pit as 
the standard, and hence thereafter clock pits are always detected over the 
entire disk area. As the clock for generating the detection window, the 
clock generated by the fixed oscillator such as a crystal oscillator as 
shown in FIG. 32 which is not in synchronism with the reproduction signal 
may be continuously used. Alternatively, a phase-locked oscillator 196 
using the detected clock pit as the reference signal and a clock switching 
circuit 197 may be provided as shown in FIG. 33. Once a clock pit is 
detected in this case after starting and the clock synchronized to the 
clock pit is obtained, more stable clock pit detection is made possible by 
using this synchronized clock. Further, instead of this phase-locked 
oscillator 196, the output 18 of the servo clock generating circuit 10 
which will be described later may be used. The clock pit detection signal 
17 thus obtained is inputted to the data clock generating circuit 11 and 
the servo clock generating circuit 10 as the reference signal thereof. In 
the same way as in FIG. 22, the data clock generating circuit 11 has an 
output clock frequency changed by an external signal. In the same way as 
in the data clock generating circuit 11, the servo clock generating 
circuit 10 is also a PLL. Since its frequency counter divisor is fixed, 
however, the servo clock generating circuit 10 need not have the variable 
frequency counter divisor function of the frequency counter 104 as shown 
in FIG. 23. With reference to FIG. 31, the servo clock output 18 of the 
servo clock generating circuit 10 is inputted to the A/D converter 6 to 
perform digital conversion of the reflected optical signal. The servo 
information timing signal 31 generated by the servo clock generating 
circuit 10 is inputted to the servo information detection circuit 8 to 
detect servo information. ID information obtained by the reflected optical 
signal is recorded with the same data clock frequency as that of 
postscript data. As shown in FIG. 31, either the servo clock 18 outputted 
from the servo clock generating circuit 10 or the data clock 19 outputted 
from the data clock generating circuit 11 is switched by a selection 
circuit 32 so as to be inputted to the A/D converter 6. 
FIG. 34 shows an example of a configuration of a drive apparatus using an 
optical disk having the format shown in FIG. 29. In FIG. 34 as well, 
components having the same functions as those of FIGS. 1, 11, 14, 20 and 
31 are denoted by like numerals, and description of the same will be 
omitted. The clock pit detection signal 17 is inputted to a clock 
generating circuit 11' to generate the clock 19 which is used to reproduce 
servo information and record and reproduce user data. An example of a 
configuration of the clock generating circuit 11' is shown in FIG. 35. The 
circuit of FIG. 35 forms a PLL. The same components as those of FIG. 23 
are denoted by like numerals. The outputted clock 19 has a frequency which 
is a frequency counter divisor times as high as that of the inputted clock 
pit detection signal 17 and has a phase synchronized to that of the clock 
pit detection signal 17. In the case of Table 5, the frequency counter 
divisor is 110 in the band A. Therefore, the clock 19 has a frequency 
which is 110 times the repetition frequency of the clock pit signal 17. 
Switching of the frequency counter divisor of the frequency counter 104 is 
performed by the control signal 24 supplied from a controller (not 
illustrated). A frequency counter divisor corresponding to the band 
whereto the optical pickup 3 is applying laser light is set. The clock 19 
is supplied to the A/D converter 6 to convert the reflected analog optical 
signal 15 to a digital signal. The servo information timing signal 31 
obtained by decoding the output of the frequency counter 104 in a decoder 
106 is supplied to the servo information detection circuit 8 to detect 
servo information. In every band, the distance between the clock pit and a 
wobble pit is equivalent to the same number of clocks of that band as 
described before. By forming the frequency counter 104 with a counter 
circuit for counting clocks starting from the clock pit, therefore, the 
decoder 106 need not switch the decode value from band to band. The output 
of the A/D converter 6 is supplied to the selection circuit 26 as well. 
The ID signal of the sector formed by prepits is thus supplied to the 
demodulation circuit 13. The clock 19 is supplied to the A/D converter 7, 
the demodulation circuit 13 and the modulation circuit 12 as well at the 
same time. The A/D converter 7 converts the signal 16 detected by optical 
magnetic effect to a digital signal. The output of the A/D converter 7 is 
supplied to the demodulation circuit 13 via the selection circuit 26. The 
demodulation circuit 13 demodulates its input signal in accordance with a 
predetermined rule and supplies a resultant signal to a higher rank 
apparatus (not illustrated). The modulation circuit 12 modulates data 
supplied from the higher rank apparatus by using the clock 19 in 
accordance with a predetermined rule and supplies a resultant signal to 
the optical pickup 3 as the recording signal 14. 
For setting the frequency counter divisor of the frequency counter 104, it 
is necessary to know the position of the optical pickup 3. As the method 
for detecting the position of the optical pickup, there are typically a 
method of detecting the position of the optical pickup directly by an 
external scale and a method of detecting the position of the optical 
pickup by referring to the track number of the sector recorded on the 
disk. For the purpose of reducing the apparatus size, however, the 
external scale tends to be not used. Further, for detecting the track 
number, a correct frequency counter divisor setting, correct servo 
information detection, and correct focus and tracking control are 
required. Therefore, the method of detecting the track number is not 
effective to the position detection for setting the frequency counter 
divisor. As a solution, at the time of seeking, it is decided beforehand 
which band the desired track belongs to and a frequency counter divisor is 
set. When an out-of-servo state has occurred at the of start or for some 
reason, frequency counter divisors of respective bands are set one after 
another. When servo information is correctly detected and the track number 
and the sector number can be read, the position of the optical pickup 3 
can be definitely fixed. As another method, the optical pickup is forcibly 
moved to the innermost band or the outermost band and the frequency 
counter divisor of the innermost band or the outermost band is set to 
detect servo information. After these operations, the drive apparatus is 
brought into the stand-by state. 
Any of the embodiments heretofore described relates to an optical magnetic 
disk and its drive apparatus. However, the application range of the 
present invention is not limited to them. The present invention can be 
applied to a perforated optical disk and its drive apparatus, an optical 
disk of the phase change type and its drive apparatus, and various disks 
such as a ROM disk on which all data are recorded by prepits and a partial 
ROM disk having a mixture of a ROM area, a rewriting area, and a write 
once area on its single disk, and drive apparatuses using these disks. 
&lt;Embodiment 6&gt; 
FIG. 36 shows an example of an information recording and reproducing 
apparatus using a ROM optical disk of the perforated, phase change type. 
In FIG. 36 as well, the same components as those of the above described 
FIGS. 1, 11 and 14 are denoted by like numerals. The portion performing 
the same operation will not be described. In these optical disks, data are 
read as a change of the quantity of reflected light in the same way as the 
servo prepit signal. FIG. 36 shows an example in which the A/D converter 
used for digital conversion of the reproduced signal is formed by a single 
A/D converter 6. As for the conversion clock, the servo clock 18 or the 
data clock 19 is switched by a selection circuit 27 so as to be used 
depending upon whether the area is the servo area or the data area. As a 
matter of course, two A/D converters may also be used as in the above 
described example. 
In accordance with the present invention, an information recording medium 
using the sample servo method is divided into a plurality of bands in the 
radial direction and a different information recording period is set for 
each band as heretofore described. Thereby, an information recording 
medium, an information recording and reproducing method, and an 
information recording and reproducing apparatus making it possible to 
increase the recording capacity as compared with a medium whereto 
recording is always conducted at intervals of a constant period. 
Further, the width of each band in the radial direction is set so that the 
number of data recorded in the data area sandwiched between servo areas 
may differ between adjacent bands while taking one byte as the unit. 
Thereby, an information recording medium, an information recording and 
reproducing method, and an information recording and reproducing apparatus 
making it possible to increase the recording capacity efficiently can be 
realized. 
Further, while keeping the time length of the servo area constant 
irrespective of the band, adjustment of the position and phase of 
recording and reproducing data is facilitated without the necessity of 
providing a gap between the servo area and the data area. Alternatively, 
the time length of the servo area is made variable according to the band. 
Thereby, an information recording medium, an information recording and 
reproducing method, and an information recording and reproducing apparatus 
making it possible to increase the recording capacity most efficiently can 
be realized. 
In addition, the head position of at least one sector included in sectors 
of each track is aligned in the radial direction. Thereby, an information 
recording medium, an information recording and reproducing method, and an 
information recording and reproducing apparatus making it possible to 
shorten the detection pull-in time of a sector can be realized. 
Further, the sector mark and ID information at the head of each sector are 
recorded and reproduced with the same data period as that of servo 
information. Thereby, an information recording medium, an information 
recording and reproducing method, and an information recording and 
reproducing apparatus shortening the time for sector detection and ID 
information reading can be realized.