JPH06176546A - Sector mark detector - Google Patents

Abstract

PURPOSE:To detect the sector mark in plural recording regions of different recording frequencies with a sector mark detecting circuit operated by the basic clock of one recording region. CONSTITUTION:This sector mark detecting device has the first sector mark detecting circuit 25 having a detecting capacity X1 and the second sector mark detecting circuit 26 provided with the detecting capacity X2 lower than the detecting capacity X1. The sector mark in the recording region WB is detected by the second sector mark detecting circuit 26 operated by the recording frequency (basic clock CK4) of the recording region WA,. As result, the detection rate of the sector mark at the time of the seek operation near to the boundary BO of the plural recording regions of the different recording frequencies is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sector mark detecting apparatus suitable for application to, for example, a magneto-optical disk recording / reproducing apparatus.

[0002]

2. Description of the Related Art An optical disc such as a magneto-optical disc is a recording medium which is divided into a plurality of sectors and information is recorded in each sector.

FIG. 4 shows a recording format of a general optical disc 1. In this optical disc 1, a recording area is formed in a spiral shape from the inner side to the outer side in the radial direction R in units of sectors S. One spiral-shaped lap is called one track. Note that the concentric shape may be used instead of the spiral shape.

This optical disk 1 is a CAV (Constant Angu
lar Velocity) method, that is, the method in which the rotation speed of the spindle motor and the recording / reproducing frequency are constant,
The length of the sector S in the circumferential direction φ gradually increases from the inner side to the outer side in the radial direction R.

Each sector S of the optical disc 1 is composed of a header portion H and a data portion D. In the header portion H, a track number and a sector are provided in advance by a stamper in addition to a sector mark SM indicating the beginning of each sector. Number ID
Information and the like are recorded as read-only information. Each sector mark SM is, for example, a fixed (same) pattern in which source bits are specifically modulated and converted into channel bits and "1" or "0" are arranged in a specific order. The track number and the like following the sector mark SM are recorded as channel bits in which the source bits are 2-7 modulated.

Recording / reproduction with respect to the optical disc 1 having the above-described structure (In this specification, unless otherwise specified, the term recording / reproduction means recording and / or reproduction. }, A recording / reproducing command is supplied from the host controller to the optical disk device accommodating the optical disk 1. This recording / reproducing command includes, for example, the head track number and sector number of the recording / reproducing area to be recorded / reproduced, that is, the head address, and the number of sectors to be recorded / reproduced from the sector S of this sector number, so-called sector length. Each information of is included.

Therefore, at the time of seek, first, the head detects the sector mark SM in order to search for the track having the head sector number designated by the recording / reproducing command, and the specific pattern (VFO) following the detected sector mark SM is detected. The track number and the sector number, which are the ID information, are read in synchronism with the code pattern), and the recording / reproducing process is performed on the data portion D following them.

Therefore, when the recording / reproducing process is performed on the optical disc 1, it is essential to detect the sector mark SM, and therefore the optical disc device is provided with a sector mark detecting circuit.

FIG. 5A is a diagram showing a part of one track T, that is, about two sectors S, and FIG. 5B is a simplified and enlarged example of a sector mark SM formed by a stamper. It is the represented diagram. Note that FIG. 5B is also referred to as a mark signal Sm reproduced as necessary.

As can be seen from FIGS. 5A and 5B, in each sector mark SM, the high level "1" indicates the basic clock (clock having the basic frequency of the recording / reproducing clock).
High-level part 1 that continues for 10 clocks (CK) with CK
A mark signal having a low level portion 12 in which 1 and subsequent "0" are continuous for 6 clocks, a high level portion 13 for 10 clocks, a low level portion 14 for 6 clocks and a high level portion 15 for 10 clocks. It is Sm.

FIG. 5C is a diagram used for explaining the operation of the sector mark detection circuit having the detection capability X ₁ .

That is, in this example, so-called don't care (don't ca) is not taken into consideration for each one clock at both ends (front and back) of each of the continuous high and low level portions 11 to 15.
re) area (area surrounded by a dotted line) dc, the detection limit for the high level portion 11 is 8 clocks, and hereinafter, for each of the high and low level portions 12 to 15, 4, 8,
The detection limit is set to 4,8 clocks. Therefore, this detection capability X in the sector mark detection circuit is
_When a pulse train having a total of five high / low level portions 11 to 15 is detected at ₁ , it is determined that the sector mark SM can be detected, and the recording / reproducing operation for the sector S is started. As shown in FIG. 5C, the optical disc 1 is provided with a slight margin (one clock at each end) for the detection capability X ₁ for the mark signal Sm.
Defects and sector mark SM read as RF signal
This is because the error in binarizing the signal having the information of 1 is considered.

If the detection capability is too low, that is, if the don't care area dc is too wide, the probability of false detection increases, which is a practical problem.

Therefore, conventionally, only one sector mark detection circuit having such a specific detection capability X ₁ determined from a system standpoint is provided.

[0015]

By the way, recently, various contrivances have been adopted as a recording format of an optical disk in order to increase the recording capacity.

FIG. 6 schematically shows the structure of an optical disc 21 having such a recording format. In this optical disk 21, a recording area W _A inside in the radial direction R
And the outer recording area W _B have different frequencies of the basic clock for recording and reproduction. The frequency of the basic clock of the recording area W _B on the outer peripheral side is increased (the basic clock of the recording area W _A is called CK _A , and the basic clock of the recording area W _B is called CK _B ). As a result, the length of the sector SM on the recording area W _B side in the circumferential direction φ is apparently shortened to increase the recording density, and as a result, the recording capacity of the optical disc 21 as a whole is increased.

In this case, the pattern arrangement order of the mark signal Sm of the sector mark SM in each of the recording areas W _A and W _B is the same as that shown in FIG. 5B.

[0018] Therefore, when recording and reproducing the recording area W _A operates the said sector mark detection circuit with the basic clock CK _A used in the recording area W _A, whereas, with respect to the recording area W _B When recording and reproducing by using the basic clock C having different frequencies used in the recording area W _B
The sector mark SM can be detected by operating the sector mark detection circuit with K _B.

However, for example, the recording areas W _A , W
During the seek operation to the vicinity of the boundary BO of _B, for example, when a seek command that causes the head 23 from the relatively inside of the recording area W _A is moved to the relatively outside of the recording area W _A is issued , Sector mark detection circuit to the recording area W _A
The sector mark SM must be detected by operating with the basic clock CK _A used in the above. In this case, the head 23 may move to the recording area W _B side due to the inertia of the head 23 ( 6 (see locus 22 in FIG. 6). In such a case, there is a problem that the sector mark SM existing in the recording area W _B cannot be detected.

The case where it cannot be detected will be described in more detail.

FIG. 7A shows a sector mark detection circuit having a detection capability X ₁ and a mark signal Sm (mark signal Sm) of a recording area W _A read from the optical disk 21 by the head 23.
_A. Figure 5B is reprinted. However, the high and low level portions are referred to as 11A to 15A. ) Shows the waveform. FIG. 7B shows the waveform of the mark signal Sm _{B in} the recording area W _B. FIG. 7C shows the detection capability X ₁ of the sector mark detection circuit (FIG. 5C is reprinted).

As can be seen from FIGS. 7A and 7C, according to the sector mark detection circuit having the detection capability X ₁ , the mark signal S
high and low level portions 11A~15A of m _A can detect all (in FIG. 7A, and. that indicated by ○ mark), it is possible to detect the sector mark SM. on the other hand,
As can be seen from FIGS. 7B and 7C, the sector mark detection circuit having the detection capability X ₁ cannot detect the first and last high level portions 11B and 15B of the mark signal Sm _B (FIG. 7B). (Indicated by a cross inside.)
Therefore, the sector mark SM cannot be detected.

If the sector mark SM cannot be detected, there are problems that the seek operation does not converge or the convergence time is considerably long.

The present invention has been made in consideration of these problems.
For example, the recording area W _AWith the base clock of
Recording area W in the operating sector mark detection circuit_BDuring ~
Sector mark that can detect even the sector mark of
An object of the present invention is to provide a peak detection device. Also,
Ming shows the sector marks in recording area A and recording area B together.
Provides a sector mark detection device that enables detection
The purpose is to do.

[0025]

The present invention is described in, for example, FIG.
, A sector mark detection circuit for detecting sector marks from a recording medium 21 in which an information signal is recorded in each sector of a plurality of divided sectors and which has a sector mark indicating the beginning at the beginning of each sector. At least 2
The sector mark detecting circuits 25 and 26 have different detection capabilities X ₁ and X ₂ , and the sector mark detecting circuits 25 and 26 are switched and operated according to a recording / reproducing command or the like. .

Further, according to the present invention, for example, as shown in FIG. 3, an information signal is recorded in each sector of a plurality of divided sectors, and a sector mark indicating the beginning is provided at the beginning of each sector. At least two sector mark detection circuits for detecting sector marks from the recording medium 21 are provided,
The sector mark detection circuits 25 and 25a are operated in parallel with different operation basic clock frequencies.

Further, according to the present invention, the recording medium 21 is a recording medium 21 having areas W _A and W _B having different recording frequencies for recording the information signal.

Furthermore, according to the present invention, the recording medium is a disk-shaped recording medium 21.

[0029]

According to the present invention, at least two sector mark detection circuits for detecting sector marks are provided, the detection capabilities X ₁ and X ₂ of the sector mark detection circuits 25 and 26 are made different, and a recording / reproducing command etc. since so as to operate by switching a sector mark detection circuit 25, 26 according to, for example, the basic clock CK _a recording area W _a
The sector mark detecting circuit 26 operating in step S1 can detect the sector mark in the recording area W _B.

According to the present invention, at least two sector mark detection circuits for detecting sector marks are provided,
Operation basic clock CK _A of the sector mark detection circuit 25, 25a, and made different frequencies CK _B, and since the parallel operated, for example, the recording area W _A and the recording area W all sectors in the _B Marks can also be detected.

[0031]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the sector mark detecting device of the present invention will be described below with reference to the drawings. In the drawings referred to below, the same reference numerals are given to those corresponding to those shown in FIGS. Further, description will be given with reference to those drawings as needed.

FIG. 1 shows a main structure of an optical disk device to which a first embodiment of the sector mark detecting device of the present invention is applied.

In FIG. 1, an optical disc 21 as a recording medium is the same as the optical disc 21 shown in FIG. That is, the frequency of the basic clock CK is different between the inner recording area W _A and the outer recording area W _B in the radial direction R. The basic clock CK _A of the recording area W _A
Reproducing frequency f _A of the recording and reproducing frequency of the basic clock CK _B recording area W _B and f _B. Also, f _A <f
_{Let's call} it _B.

2A to 2D show the recording area W._A, W_Bof
Each sector S_A, S_BThe example of composition of is shown. Figure 2A, figure
As can be seen from 2C, the recording area of the optical disc 21
W_A, W _BEach sector S_A, S_BIs the header part H_A，
H_BAnd the data part D_A, D_BThe header is
-Part H_A, H_BIn each sector S beforehand by stamper
_A, S_BSector mark SM indicating the beginning of the_A, SM_BAnd
Dress information such as track number and sector number
ID information is recorded as read-only information.

[0035] Here, each sector mark SM _A, SM _B is a mark signal Sm _A, Sm _B of similarity. That is, they have the same arrangement pattern only with different physical lengths. Each sector mark SM _A, SM _B are, 2B, 2
As shown in C, "1" is the basic clock CK _A or C
High-level part 1 that continues for 10 clocks (CK) at K _B
1A and 11B, followed by low-level portions 12A and 12B in which "0" continues for 6 clocks, high-level portions 13A and 13B corresponding to 10 clocks subsequent thereto, low-level portions 14A, 14B and 10 clocks corresponding to 6 clocks. Of the mark signal S having high level portions 15A and 15B of the minute
m _A and Sm _B.

The optical disk 21 configured as described above
Is rotated by the spindle motor 19. An information signal (header portions H _A , H) recorded on the disk surface by the head 23 which is arranged so as to face the disk surface of the optical disk 21 and is moved in the radial direction R by a linear motor and a voice coil motor (not shown). _B and the information signals of the data sections D _A and D _B ) are read as analog signals, so-called RF signals. When the optical disc 21 is a magneto-optical disc, an optical head and a magnetic head are used, and an RF signal is output from the optical head.

This RF signal is binarized and converted into a digital RF signal by an RF signal processing circuit 24 as a medium signal reading circuit having an amplifier and an A / D converter.

The digital RF signal is supplied to the first and second sector mark detection circuits 25 and 26 and the data read processing circuit 27.

The first and second clock switching control signals S ₁ and S ₂ are supplied to the control terminals of the sector mark detection circuits 25 and 26, respectively. Further, the first and second sector mark detection circuit 25, the basic clock CK _A through terminals 33 and 34 from the clock generating circuit (not shown) (frequency f _A), CK _B (frequency f _B) are both supplied ing.

Here, the first sector mark detection circuit 25
The detection capability X ₁ of the same is the same as that shown in FIG. 5C (FIG. 7C). That is, so-called don't care, which does not consider each one clock at both ends (front and back) of each of the continuous high and low level portions 11 to 15.
As the area, the detection limit for the high level portion 11 is set to 8
Clock, hereinafter high-low level parts 12-15
On the other hand, the detection limit is set to 4,8,4,8 clocks respectively.

FIG. 7F shows the second sector mark detection circuit 2
6 is a diagram provided for explaining a detection capability X ₂ of No. 6; FIG. That is, two clocks at both ends (before and after) of each of the continuous high / low level portions 11 to 15 are don't care areas, and the detection limit for the high level portion 11 is 6 clocks. The detection limit is set to 2,6,2,6 clocks for 15 to 15, respectively. In other words, the detection capability X ₂ of the _second sector mark detection circuit 26 is set looser than that of the first sector mark detection circuit 25. That loosely set, as described working after sector mark SM _A, SM _B
The false detection probability of is increased, but the non-detection (undetectable) probability is relatively reduced.

In the first sector mark detection circuit 25 or the second sector mark detection circuit 26, the sector marks SM _A ,
When the SM _B is detected, the sector mark detection pulse P is output. The sector mark detection pulse P is applied to the terminals 28b and 28c of the selector circuit 28 which is a multiplexer.
Is supplied to. The common terminal 28a is connected to the data read processing circuit 27.

A switching control signal S ₃ is supplied from the system controller 29 to the switching control terminal 28d of the selector circuit 28.

The system controller 29 has a terminal 30
Through this, various commands such as a recording / playback command and a seek command are supplied from a higher-order controller (not shown). The read data RD read by the data read processing circuit 27 is output to another circuit through the terminal 31, and is also output to a higher-order controller through the system controller 29 and the terminal 30.

Next, the operation of the example of FIG. 1 will be described.

System controller 2 through terminal 30
When the content of the command supplied to 9 is recording / reproducing of a specific recording area in the recording area W _A , the first clock switching control signal S _{1 is used} as the basic clock CK of the first sector mark detection circuit 25. The basic clock CK _A is set according to. Therefore, the common terminal 2 of the selector circuit 28
8a is connected to the first sector mark detecting circuit 25 side terminal 28b in response to the switching control signals S _3, known detection operation of the sector mark SM _A is performed.

Further, a system controller is provided through the terminal 30.
The content of the command supplied to the controller 29 is the recording area W_BWithin
If the recording / reproduction of a specific recording area of the
As the basic clock CK of the tag detection circuit 25,
1 clock switching control signal S ₁Depending on the basic clock C
K_BIs set. Common terminal 28a of the selector circuit 28
And the terminal 28b remain connected. And like
The first sector mark detection circuit 25
SM_BIs detected.

On the other hand, the content of the command supplied to the system controller 29 through the terminal 30 is a seek command, and the head sector S specified by the seek command.
If the address is on the recording area W _A side near the boundary BO between the recording area W _A and the recording area W _B , the first sector mark detection circuit 25 detects the sector mark SM _A by the conventional technique. as described in the section, it is impossible to detect the sector mark SM _B (see FIGS. 6 and 7B and FIG. 7C).

Therefore, in this case, the second sector mark detection circuit 26 is used. Therefore, the switching control signal S
Depending on _3, the common terminal 28a and the terminal 28 of the selector circuit 28
Further, the second sector mark detection circuit 26 is supplied with a _second clock switching control signal S ₂ such that the clock used by the second sector mark detection circuit 26 becomes the basic clock CK _A.

7D to 7F are diagrams used to explain the operation in this case. FIG. 7D shows the recording area W _A with the head 23.
Mark signal Sm _A which is the content of the digital RF signal output from the RF signal processing circuit 24 when seeking
Is shown. Further, in FIG. 7E (same as FIG. 7B), the head 23 moves to the recording area W _{B due} to inertia or the like, regardless of whether the seek target address specified by the seek command is an address in the recording area W _A. If R
The sector mark signal Sm _B which is the content of the digital RF signal output from the F signal processing circuit 24 is shown. In this case, as shown in FIG. 7F, the detection capability X ₂ of the _second sector mark detection circuit 26 is set to the first sector mark detection circuit 2
The sector mark signal Sm _B can be detected by the second sector mark detection circuit 26 because the sector mark signal Sm _B is looser than the detection capability X ₂ of No. 5.

Therefore, in such a case, the detectability is
Second sector mark detection circuit with different (relaxed) force
By using 26, which sector mark signal
Sm _A, Sm_BRecording area W even when is supplied
_ABasic clock CK_AThe second ma being operated on
Sector mark SM in the peak detection circuit 26_A, SM_BTogether
Can be detected. That is, for different recording frequencies
Multiple recording areas W_A, W_BSeeking near the boundary BO
Sector mark SM in body time_A, SM_BThe detection rate of
Go up.

[0052] Data read processing circuit 27, a sector mark SM _A, headers from the digital RF signal based on a sector mark detection pulse P output when the SM _B is detected portion H _A, H _B (FIGS. 2A, 2C The information signal (in this case, the address signal first) recorded in the reference) can be read, and the head 23 can surely seek to the track designated by the seek command.

[0053] According to the first embodiment described above thus has a sector mark SM _A, the first and second sector mark detection circuit 25, 26 of the two circuits for detecting the SM _B, each sector mark Since the detection capacities of the detection circuits 25 and 26 are made different and the sector mark detection circuit is switched and operated in accordance with a command or the like, for example, near the boundary BO between the recording area W _A and the recording area W _B. During the seek operation by the seek command, the sector mark S is detected by the second sector mark detection circuit 26 having a loose detection capability.
It is possible to detect M _A, the SM _B both.

Not only during the seek operation, but within the specified range of the continuous recording / reproducing command, the recording area W _A and the recording area W _B
Even if it contains a boundary BO portion, a sector mark by using the second sector mark detection circuit 26 SM _A, SM _B
Both can be detected.

Generally speaking, which one of the first and second sector mark detection circuits 25, 26 is used for which basic clock CK _A , CK _B from a system standpoint according to a recording / reproducing command or the like. May be determined by the system controller 29.

[0056] While in the example FIG describes only the reproducing system, the sector mark SM _A, detection of SM _B are also essential during the recording operation regardless of the reproduction system. Also, FIG.
In the example, the sector mark S is detected by the first and second sector mark detection circuits 25 and 26 of two circuits having different detection capabilities.
Although M _A and S M _B are detected, if another sector mark detection circuit with different detection capability is added and configured so that they can be switched and used, seek time and detection accuracy (erroneous detection probability ) And the sector mark pattern, etc., it becomes possible to perform finer control.

As a sector mark pattern, for example, a pattern standardized by ISO / IEC DIS 10090 is known, and its pattern arrangement is shown in Table 1 with 5 bytes and 80 channel bits (1 byte is 2 channel bits). As shown.

[0058]

[Table 1] 1111 1111 1100 0000 1111 1100 0000 0000 0000 1111 1100 0000 1111 1100 0000 1111 1111 1100 1001 0010

FIG. 3 shows a main structure of an optical disc device to which a second embodiment of the sector mark detecting device of the present invention is applied.

In the example of FIG. 3, the first sector mark detection circuit 25 in the example of FIG. 1 is always operated by the basic clock CK _A. Further, instead of the second sector mark detection circuit 26, a second sector mark detection circuit 25a having the same detection capability X ₁ as the first sector mark detection circuit 25 is provided.
To prepare. The second sector mark detection circuit 2
The 5a, always operates on a basic clock CK _B. In addition, the first and second sector mark detection circuits 25, 25
The output terminals of a are connected to each other, and the sector mark detection pulse P which is an output signal is supplied to the data read processing circuit 27.

That is, in this second embodiment,
Has a detection capability X ₁ relatively high, respectively, the basic clock CK _A, is both a sector mark detection circuit 25,25a to be operated in CK _B are in parallel connected configuration.

With this configuration, the recording area W_ANote
During recording / reproduction, the first sector mark detection circuit 25 must be
By sector mark SM_ADetected sector mark
The detection pulse P is output, while the recording area W_BRecord again
Be sure to use the second sector mark detection circuit 25a during life.
Therefore sector mark SM_BSector mark detection
Since the output pulse P is output,
Recording area W _AAnd recording area W_BWhen you make a round trip between
Even if the sector mark detection pulse P is output,
You can

[0063] Thus, according to the three examples Fig sector mark SM _A, first and second of the two circuits for detecting the SM _B
Of the sector mark detection circuits 25 and 25a, and the operation basic clock C of each sector mark detection circuit 25 and 25a.
K _A, the recording area the frequency of CK _B W _A, W recording frequency f _A of _B. Set f _B, and since the parallel operated, it is possible to record area W _A and the recording area W any sector mark SM _A in _B, also SM _B detected.

According to the second embodiment, when there are three or more recording areas having different recording frequencies, the sector mark detecting circuits having the same detecting ability are connected in parallel in correspondence with the number. Of course, all you have to do is do it.

It is also possible to combine the first embodiment and the second embodiment.

Furthermore, the present invention can be applied to magnetic disks such as floppy disks and hard disks in addition to optical disks such as magneto-optical disks. It can also be applied to recording media other than disk-shaped recording media.

The present invention is not limited to the above-mentioned embodiments, and it goes without saying that various configurations can be adopted without departing from the gist of the present invention.

[0068]

As described above, according to the present invention,
At least two sector mark detection circuits for detecting sector marks are provided, the detection capabilities of the respective sector mark detection circuits are different, and the sector mark detection circuits are switched and operated according to a recording / reproducing command or the like. Therefore, for example, the sector mark detection circuit operating with the basic clock of one recording area can detect the sector mark in the other recording area recorded with the basic clock of a different frequency.

According to the present invention, at least two sector mark detection circuits for detecting sector marks are provided,
Since the frequency of the operation basic clock of each of the above sector mark detection circuits is different and they are operated in parallel, for example, like the above invention, the sector mark detection circuit operated by the basic clock of one recording area is detected. The circuit can also detect the sector mark in the other recording area recorded with the basic clock of a different frequency.

The present invention is particularly suitable for application to a disc-shaped recording medium such as an optical disc.

[Brief description of drawings]

FIG. 1 is a diagram showing a main configuration of an optical disc recording / reproducing apparatus to which a first embodiment of a sector mark detecting apparatus of the present invention is applied.

2 is a diagram showing a configuration of a sector of the optical disc in the example of FIG. 1. FIG.

FIG. 3 is a diagram showing a main part configuration of an optical disc recording / reproducing apparatus to which a second embodiment of the sector mark detecting apparatus of the present invention is applied.

FIG. 4 is a diagram used for explaining a recording format of a CAV type optical disc.

FIG. 5 is a diagram for explaining the operation of a conventional sector mark detection circuit.

FIG. 6 is a diagram provided for explaining a recording format of an optical disc having recording areas having different recording frequencies.

7A to 7C are diagrams for explaining the operation of the conventional technique. FIGS. 6A to 6F are diagrams for explaining the operation of the embodiment.

[Explanation of symbols]

21 optical disk 25 first sector mark detection circuit 26 second sector mark detection circuit X ₁ , X ₂ detection capability

Claims (4)

[Claims] 1. A sector mark detection circuit for detecting a sector mark from a recording medium in which an information signal is recorded in each sector of a plurality of divided sectors and which has a sector mark indicating the beginning at the beginning of each sector. A sector mark detection device having at least two circuits, wherein the detection capabilities of the respective sector mark detection circuits are different, and the sector mark detection circuits are switched and operated according to the contents of a recording / reproducing command. 2. A sector mark detection circuit for detecting a sector mark from a recording medium in which an information signal is recorded in each sector unit of a plurality of divided sectors and which has a sector mark indicating the beginning at the head of each sector. A sector mark detecting device which has at least two circuits and is operated in parallel with different frequencies of the operation basic clocks of the sector mark detecting circuits. 3. The sector mark detecting device according to claim 1, wherein the recording medium is a recording medium having areas having different recording frequencies for recording the information signal. 4. The sector mark detecting device according to claim 1, wherein the recording medium is a disk-shaped recording medium.