A DISC DEVICE AND A DISC-LIKE RECORDING MEDIUM

Abstract: The optical disc (1) has a record track (2), on which servo signal regions (3) and address signal regions (4) are formed alternately along the circumference. Two or more records using different physical changes are provided for the address signal regions (4), yet each region has only one means of physical change. For instance, one region is recorded in the form of pits and the next one is recorded opto-magnetically. switching between the two units is made when the pick-up is in the servo signal region, so leaving enough time margin for the operation.

Description: This invention relates to a disk device for at least reproducing an opto-magnetic disk or the like and a disk-like recording medium employed in such device. More particularly, it relates to a disk device for reproducing a disk on which time sharing servo signals, such as so-called sector servo signals, are previously recorded on the disk, and to a disklike recording medium, such as the aforementioned opto-magnetic disk. Recently, the disk like recording media, such as optical disks or photo magnetic disks utilizing the optical or magneto-optical signal recording/reproducing method, have been evolved and presented to the market. These disk-like recording media may be classified into three types of disks according to their recording format. These are a so-called read-only memory or ROM type disk, like the digital audio disk, such as a compact disk or CD, or the video disk, in which various information signals are previously recorded by the manufacturer on the disk-like recording medium unrewritably and provided in this form to the users, a so-called programmable ROM or PROM type disk, also called DRAW or write once type, in which the information signals can be written only once by the users, and a so-called random access or RAM type disk, like the opto-magnetic disk, in which recorded information signals can be erased and rewritten. European Published Patent Application EP-A-0 189 187 discloses such a disk, in which address information is written in the form of embossed pits. Means for switching between the data signal recorded magnetically and the address signal are provided These various type disks have evolved separately and at different times so that they make use of distinct formats. Because of the lack of interchangeability among these various type disks, and the resulting inconveniences to both the users and the manufacturers, a demand for unifying the formats has been raised by both the users and the manufacturers. As a technology to realize the unified format, it is proposed to introduce the concept of a so-called sampling servo according to which, similarly to the so-called sector servo in a hard disk in the field of magnetic disks, servo signals are recorded at a prescribed interval or angular interval on concentric or convolute tracks on the disk, these discrete servo signals being sampled and held during the disk revolution to effect continuous servo control. Such sampled servo formats are e.g. known from JP-A-57 181 429 or IBM Technical Disl. Bull. Vol 26, No 7B, p. 3956-3957. The disk of the unified format allows not only that the signal recording format of a disk is limited to one of the several recording formats, but also that signals are recorded in two or more recording formats on one disk. In the case of an opto-magnetic disk, for example, the servo and address signals are previously recorded by a so-called embossing such as by mechanical pits or a pattern of projections and recesses, or bumps, and the data signals are photo-magnetically recorded by the user. It is noted that, in the aforementioned reproducing for the above-mentioned opto-magnetic disks, the light reflected by the recording surface is split by a beam splitter operating on the principle of light polarization so as to be detected by two photodetectors and the detected signals supplied from these photodetectors are summed to produce the address signals and servo signals recorded in the form of pits. The photo-magnetically recorded data signals are obtained by subtraction of the respecive detected signals. The servo signals are processed by a servo signal circuit system from the aforementioned summed output signals, however, as for the address and data signals, a switching operation is required, for example at an input portion of the A/D converter of the reproducing signal processing system, for supplying address and data signals after switching, since the signal processing system processes in a time-sharing manner. However, when the address signals recorded in the form of pits and the photo-magnetically recorded data signals are formed consecutively in one data/address signal region 4 between servo regions 3 on one track 2, as shown in Fig. 9, it becomes necessary that the aforementioned switching be carried out instantaneously at the time point of shift from the address signal recording region to the data signal recording region during reproduction, so that the switching during the time interval shorter by about one digit than the interval of a window of a channel clock. Especially, when the disk is driven at a faster speed, with the higher data transfer rate, an extremely fast switching operation of the order of several nanoseconds is required which increases the hardware load. Such a system is difficult to realize and expensive. It is noted herein that Fig. 9 shows the recording format for an arbitrary track and the pits P as shown diagrammatically at B in Fig. 9 are such as those in practice formed for the recording format shown at A in Fig. 9. It is therefore an object of the present invention to provide a disk device for at least reproducing a disk-like recording medium in which signal recording may be made in two or more physical recording formats between the servo signal regions, wherein, according to the present invention, the switching from one to the other of the physical signal recording formats at the time of reproducing the recording medium may be made with a timely margin. On the other hand, although it may be contemplated that signals be recorded in one data/address signal region 4 in accordance with one physical change, the number of bytes in one data/address signal region 4 is usually more than the number of bytes of the address data of one sector, so that, for effective utilization of the recording region, it may occasionally be desirable that the signal be recorded together by two or more physical changes in one region 4. It is therefore an object of the present invention to provide a disk-like recording medium in which signals may be recorded between the servo signal regions in two or more physical changes, wherein, according to the present invention, the switching from one to the other of the physical signal recording formats at the time of reproducing the recording medium may be made with a timely margin. According to a first aspect of the present invention, there is provided a disk apparatus for at least reproducing a disk-shaped recording medium wherein servo signal regions in which pits for tracking are recorded at alternately offset positions with respect to the center of the track and pits for clock generation are recorded at the center position of the track, as servo signals, and data/address signal regions into which at least data signals and address signals are written are formed alternately in the circumferential direction of the disk, and wherein signals are recorded in either a first format by a first kind of physical change of the medium or a second format by a second kind of physical change of the medium in said data/address signal regions, wherein the disk apparatus comprises a pickup for reading out said signals recorded in said first and second formats, and means for switching between said signals recorded in said first format and said signals recorded in said second format, said switching taking place in said servo signal region. In the present disk device, switching among the signals of plural recording formats different from one another may be carried out during the time the servo signal regions are scanned such that a sufficient time can be provided for switching despite occasionally increased data transfer speed, with the result that the signal switching can be achieved with a timely margin or allowance. According to a second aspect of the present invention, there is also provided a disk-shaped recorded medium having circumferential tracks containing alternating servo signal regions in which pits for tracking are recorded at alternately offset positions with respect to the center of the track and pits for clock generation are recorded at the center position of the track, as servo signals, and data address signal regions into which at least data signals and address signals are written in either a first format by a first kind of physical change of the medium or a second format by a second kind of physical change of the medium, whereby at least some signals recorded in said first physical format and at least some signals recording in said second physical format are separated by one of said servo signal regions. In the present disk-like recording medium, in case wherein signal recording is made in one data/address signal region by two or more physical changes, the reproducing signals can be switched with a margin at the no-signal recording region provided between the signal recording portions. Figure 1 is a diagrammatic view showing a recording format for each track in an embodiment of the disk-like recording medium according to the present invention; Figure 2 is a diagrammatic view showing a recording pattern for an opto-magnetic disk in the above embodiment; Figure 3 is a diagrammatic view showing the arrangement of the respective pit regions; Figure 4 is a diagrammatic view showing the array of the pits along the radial direction of the disk; Figure 5 is a block diagram showing the overall construction of the opto-magnetic disk device employing the disk-like recording medium; Fig. 6 is a diagrammatic view showing the recording format of each track in a modified embodiment of the disk-like recording medium according to the present invention; Fig 7 is a diagrammatic view showing the recroding format of each track in another modified embodiment of the disk-like recording medium according to the present invention; Fig. 8 is a diagrammatic view showing a specified example of the record contents in one data/address signal region in the embodiment shown in Fig. 7; and Fig. 9 is a diagrammatic view showing the recording format of each track for understading the present invention. An opto-magnetic disk according to an embodiment of the present invention will be explained by referring to the drawings. In Fig. 1, there is diagrammatically shown a recording format of a given track 2 of the opto-magnetic disk 1 of the present embodiment (see Fig. 2) wherein pits P shown at B are recorded for the recording format shown in Fig. 2. Referring to Figs. 1 and 2, servo signal regions 3 in which servo signals are recorded in the form of pits and data and address regions 4 in which are written at least data signals and address signals are alternately formed along the circumferentially extending tracks 2 of the disk 1. In the data and address signal regions 4, the address signals are recorded by pit formation as a first physical change, while the data signals in general are recorded by opto-magnetic recording as a second physical change. In one of the data and address signal regions 4, only one of the address and data signals are recorded selectively. The overall arrangement for recording/reproducing such opto-magnetic disk 1 is shown in Fig. 5 wherein an optical pickup 20 reads out the address and data signals as the recording signals by the first physical change, while a multiplexer 63 is provided as a switching means for switching between the address and data signals from the optical pickup 20. The switching between these signals by the multiplexer 63 is caused to occur during the time of scanning of the servo signal regions. The recording pattern on the opto-magnetic disk 1 and the recording format on the track will be explained in more detail. Referring first to Fig. 1, the opto-magnetic disk 1 of, for example, a 5-inch type, has a diameter of the order of 13 cm, and a storage capacity of not less than 300 M bytes per side. The disk 1 is revolved at a constant angular velocity and, assuming that a track is formed with each disk revolution, tracks 2 are formed, e.g. concentrically, for recording the data. About 18000 to 20000 tracks are formed on one side with each track being divided into, for example, 32 sectors. Each track 2 consists of servo signal regions 3 in which servo pits are recorded and formed and data/address signal regions 4 into which data and address signals are written, as shown to an enlarged scale in Fig. 1, these regions being alternately formed along the circumferential direction. Several tens of sets of the servo signal regions and the data/address signal regions 4 are provided in each sector. The servo signal region 3 has the length, calculated as a number of bytes, equal to, for example, two bytes, while the data/address signal region 4 has the length, calculated as a number of bytes, equal to, for example, 13 bytes. In each servo signal region 3, three pits P A , P B and P C are formed, as shown in Fig. 3. These pits P A and P B are formed with a vertical shift on both sides of a centerline of a track formed on the opto-magnetic disk 1 indicated by a chain dotted line, whereas the pit P C is formed on the centerline. These pits P A , P B and P C are about 0.5 to 1.0 micron in diameter, while the actual length L of the servo signal region 3 is about 15 to 30 microns, as an example. Fig. 4 shows the array of the pits P A , P B and P C along the radial direction of the disk, that is, the direction shown by the arrow mark in Fig. 2. Thus the pits P B and P C are arranged linearly, whereas the pits P A are arrayed with a shift longitudinally of the track at intervals of n pits, for example, 16 pits. The pit array with a shift at intervals of n pits is utilized for performing a traverse count for the optical pickup to find the track number being scanned, as described later. The pits P A are sampled by sampling pulses SP₁ or SP₂, while the pits P B and P C are sampled by sampling pulses SP₃, SP₅ and the mirror surface region between the pits P B and P C is sampled by sampling pulses SP₄ for producing various servo and clock signals as later described. Thus the servo signals of the present embodiment are used for performing a variety of control operations including focusing, tracking, clocking and traverse counting. At least sector-wise address and data signals are recorded in the data/address signal regions 4 between the servo signal regions 3. Assuming that the effective data for one sector are comprised of, for example, 512 bytes, and additioinal information and error detection/correction codes are recorded besides the effective data, a total of 670 to 680 bytes are recorded in one data sector. With a length of the data/address signal region 4 of 13 bytes, about 52 data/address signal regions 4 collectively constitutes one sector. Thus, one address signal region 4a is provided to, for example, 52 data signal regions 4b. It is noted that the recording in one given data/address signal region 4 is effected with a recording format of a given physical change such that two or more different physical changes do not exist simultaneouly. Thus, in the present embodiment, each data/address signal region 4 is allotted exclusively to the address signal region 4a or to the data signal region 4b, such that the sector wise-address information is previously recorded in the address signal region 4a in the form of pits similarly to the recording of the servo signals and the data signals broadly including the aforementioned additional information and the error detection/correction codes are adapted to be recorded photo-magnetically only in the data signal region 4b. The switching between the address and data signals at the time of reproduction is performed during the time the servo signal region 3 is scanned by the pickup 20. The servo signal area 3 has a length of 2 bytes, for example, as discussed above, so that a sufficient time allowance is provided to effect the signal switching. Referring now to Fig. 5, the opto-magnetic disk apparatus for recording/reproducing the aforementioned the opto-magnetic disk 1 will be explained by referring to Fig. 5. In Fig. 5, data to be recorded D₁ are supplied from, for example, a computer, through an interface to an input terminal 11. These data D₁ are then supplied to a modulating circuit 12 where they are subjected to modulation including bit conversion, after which they are supplied to a laser drive circuit 13. Control signals of the write, read-out or erasure modes are supplied to the laser drive circuit 13, which is responsive thereto to issue drive signals for driving a laser diode 21 of an optical pickup 20 while also issuing drive pulse signals to the laser diode 21 during data recording and erasure at the timing of the channel clocks CCK acting as the reference clocks and high frequency drive signals during read-out to the same laser diode 21. The optical pickup 20 includes, in addition to the laser diode 21, a photo-diode 22 and two photodetectors 23, 24 each divided into four portions. The photo-diode 22 senses the intensity of the laser beam emitted by the laser diode 21. The photodetectors 23, 24 detect the aforementioned laser beam reflected by the opto-magnetic disk 1 by analyzers, with one of the photodetectors detecting the positive direction component of the kerr angle of rotation and the other the negative direction component of the kerr angle of rotation. An electric motor 14 is servo-controlled from a motor servo circuit 15 through, for example, a phase locked loop or PLL, for causing revolutions of the opto-magnetic disk 1 accurately at a prescribed velocity (angular velocity). The laser beam outputted from the aforementioned laser diode 21 is irradiated on the opto-magnetic disk 1, while also falling on the photodiode 22. The output of the photodiode 22 is supplied through a d.c. amplifier circuit 16 to a sample and hold circuit 17 (S/H) in an amount related with the laser beam intensity. In the S/H circuit 17, sample hold operation is performed by the sampling pulses SP₄, see Fig. 4, and the output from the S/H circuit is supplied through an APC amplifier circuit 18 to the laser drive circuit 13 as the automatic power control or APC signals. In this manner, the intensity of the laser beam outputted from the laser diode 21 is maintained at a predetermined value. The respective outputs of the photodetectors 23, 24 of the optical pickup 20, on which the laser beam falls after reflection by the opto-magnetic disk 1 through an analyzer, not shown, are supplied to a preamplifier 31. A light detection signal S A which is the sum signal of the outputs of the respective light receiving regions of the photodetectors 23 and 24, wherein S A =A+B+C+D+A'+B'+C'+D' inclusive of d.c. components, is directly supplied to a focus servo circuit 32, whereas a light detection signal S B composed of the outputs of the respective light receiving regions, wherein S B =(AC-BD) + (A'C'-B'D') , is supplied to the focus servo circuit 32 through the S/H circuit 33 adapted for effecting a sample and hold operation at the timing of the sampling pulses SP₄. Focus servo control signals, generated at the focus servo circuit 32 on the basis of the signals S A and S B , are supplied to the optical pickup 20 to effect a focus control. A light detection signal S C from the preamplifier 31, wherein S C =A+B+C+D+A'+B'+C'+D , is supplied to each of a peak position detecting circuit 41, S/H circuits 51, 52 and 53 and to a sampling clamp circuit 61. The light detection signal S C is the signal detecting the pit patterns or patterns of recesses and projections in the servo signal region 3 and the address signal region 4a of the disk 1. In the peak position detecting circuit 41, the peak position of the light detection signal S C is detected. In a proper or intrinsic pattern detecting circuit 42, the pit pattern having an interval proper or intrinsic only to the interval between the pits P B and P C on the disk 1 is detected to detect the pit P C , with the detection output being supplied through a delay circuit 43 to a pulse generator 44. Based on the detection output obtained in the proper pattern detecting circuit 42, the pulse generator 44 generates channel clocks CCK as reference clocks synchronized with the above pits P C , while simultaneously generating byte clocks BYC, servo byte clocks SBC and sampling pulses SP₁, SP₂, SP₃, SP₄ and SP₅, see Fig. 4. The channel clocks CCK are supplied to all of the circuit blocks, in a manner not shown. The sampling pulses SP₁, SP₂ and SP₃ are supplied to the S/H 51, 52 and 53, respectively. The sampling pulses SP₄ are supplied to the S/H circuit 17, 33 and to sampling clamp circuits 61, 62. The sampling pulses SP₅ are used, for example, for detecting the movement direction of the optical pickup 20. Gating pulses are supplied from the pulse generator 44 to the peak position detecting circuit 41 and to the proper position detecting circuit 42. In the S/H circuit 51, 52 and 53, the supplied light detection signals S C are subjected to sample and hold operation by the sampling pulses SP₁, SP₂ and SP₃. The outputs from the S/H circuit 51 and the S/H circuit 52 are compared in the signal level by a comparator 54. The comparator outputs are inverted at intervals of the consecutive n tracks, such as 16 tracks, in connection with the array of the pits P A on the disk 1 so as to be supplied to a tracking servo/seek circuit 55 as the traverse count signals and to a multiplexer 56. One of the signals from the S/H circuits 51 and 52 that is higher in the signal level is selectively outputted from the multiplexer 56 so as to be supplied to a subtractor 57. In the subtractor 57, there is formed a difference signal between the signal from the multiplexor 56 and that from the S/H circuit 53, which difference signal is transmitted as the tracking error signal to the aforementioned tracking servo/seek circuit 55. The tracking servo/seek circuit 55 effects seek and tracking control for the optical pickup 20. The light detection signals S C and S D , wherein S D =(A+B+C+D) - (A'+B'+C'+D') are supplied from the preamplifier 31 to the sampling clamp circuit 61 and 62, respectively. The light detection signal S D is the detection signal of the data written in the data signal region 4b of the opto-magnetic disk 1. The light detection signal S C supplied to the sampling clamp circuit 61 is the detection signal of the addresses written in the region 4a. In the sampling clamp circuits 61 and 62, the respective signals are clamped by the above sampling pulses SP₄ so as to be transmitted to the above multiplexer 63. In the multiplexer 63, the switching select operation thereof is controlled by control signals from the sync detect/address decode circuit 64. Supposing that the light detecting signal S C is transmitted through the sampling clamp circuit 61 and the multiplexer 63 to an analog to digital or A/D converter 65 and thereby converted into a digital value before being transmitted to a demodulator 66, the output from the demodulator 66 is transmitted to the sync detect/address decode circuit 64 for detecting the sync signals and decoding the address information or data. The multiplexor 63 is controlled so as to be switched when the actual address coincides with the address information, supplied through an interface from a computer, of the data to be read, for example, so that the light detection signals S D for the data signal region 4b are transmitted to the A/D converter 65 and the demodulator 66 and the data D O obtained after demodulation including bit conversion are issued at the output terminal 67. These data D O are transmitted through an interface to a computer. At the time of data writing, control signals are transmitted from the sync detection/address decoding circuit 64 to the demodulator 12 and, in accordance with these control signals, the data to be written are transmitted from the demodulator 12 to the laser drive circuit 13. It is noted that the switching control operation of the multiplexer 63 is not effected within the data/address signal region 4 on the track 2, but necessarily within the scanning period of the servo signal region 3. As discussed hereinabove, the servo signal region 3 has two bytes or thereabout and the multiplexer 63 can be switched with a sufficient time allowance even when the rotational speed of the disk and hence the data transfer rate are increased. In the above embodiment, the address signals are recorded within the entire address signal region 4a of each of the data/address signal regions 4. However, as shown in Fig. 6, address signals may also be recorded on a portion of the region 4a, with the remaining portion being blank or free of signals. In this case, only one type of physical recording is effected within one region 4 so that a temporary allowance may be afforded for the switching of the reproducing signals. It is to be noted that such signal switching occurs within the servo signal, in the same manner as discussed hereinabove. In general, the number of bytes in the data/address signal region 4 is larger than the number of bytes of the address data for one sector. Therefore, when it becomes necessary for effective utilization of the recording region that signals recorded by two or more kinds of physical changes exist together within one data/address signal region 4, an unrecorded region 5c may be provided between the address signal region 5a formed in one physical signal recording format and the data signal region 5b formed in another physical signal recording format, as in the case of the opto-magnetic disk shown in Fig. 7 and the signal switching may be effected in the interval of the unrecorded region 5c during reproduction so that signal switcing may be performed with a temporary allowance. In Fig. 7, wherein the recording format of a given track 2 of the opto-magnetic disk in the present embodiment is schematically shown, similarly to the embodiment of Fig. 1, the pits P as shown at B are recorded for the recording format as at A. In Fig. 7, data/address signal regions 4 into which the data and address signals are recorded are provided between the respective servo regions 3 in which the servo signals are recorded in the form of pits, these regions 3 and 4 being alternately provided along the tracks circumferentially of the disk. In the data/address region 4, at least the address signals are recorded using pit formation as the physical change and the general data signals are recorded using opto-magnetic recording as the second physical change when both the address and data signals are to be recorded in one data/address signal region 4. It will be noted that at least the aforementioned sectorwise address and data signals are recorded in the data/address signal region 4 between the servo signal regions. For example, with the effective data within one sector being 512 bytes, data of a total of 670 to 680 bytes or thereabouts, inclusive of the additional information and error detection or correction codes, are recorded in one sector. With the length of the data/address signal region 4 being 16 bytes, 42 or more data/address signal regions 4, for example, are required for constituting data of one sector. For example, 42 of 43 data recording regions 4 will be dedicated to data recording, the remaining one being used for recording of both addresses and data. In the present embodiment, when the address and data signals are recorded together in the aforementioned data/address signal region 4, an unrecorded region 5c is formed between the address signal region 5a and the data signal region 5b. The lengths of the address signal area 5a and the data signal region 5b are a and b in terms of the number of bytes. The unrecorded region 5c directly after the address signal region 5a has a length c in terms of the number of bytes that is sufficient to perform effectively the signal switching for reproduction as described later. More specifically, such length c may be 1 byte or thereabouts. It is noted that additional data that are not required during data reproduction, such as the data detected mark or DDM concerning the aforementioned address data, may be recorded in the form of pits in the unrecorded region 5c. Also the address information is previously recorded sector-wise in the address signal region 5a in the form of pits similar to those of the servo signals, while the data signals in the broad sense of the term, inclusive of the aforementioned additional information and error detect ion/correction codes, are recorded in the data signal region 5b by so-called photo-magnetic recording. A more specific example of the data/address signal region 4 in which the aforementioned address signal region 5a, data signal region 5b and the unrecorded region 5c between these regions 5a and 5b exist together, will be explained by referring to Fig. 8. In this figure, there is recorded in the address signal region 5a within the data/address signal region 4 between the servo signal regions 3 a 1-byte sector mark SM, followed by an upper byte of the track number T M , a lower byte of the track number T L and a sector number S, each being of one byte, along with the corresponding inversion data T M , T L and S . Although these data are recorded in the example of Figure 8 in the sequence of T M , T M , T L , T L , S and S , they may be recorded in any other desired sequence, such as S, T M , T L , T L , T M and S . It is to be noted that these address data are the pre-format data previously recorded in the form of so-called pits on the medium, as described hereinabove. The address signal region 5a is directly followed by the unrecorded region 5c followed in turn by the data signal region 5b. In the data signal region 5b, there are recorded a copy protect data CP and a data deleted mark DDM, each being of 1 byte, along with the corresponding inversion data CP and DDM . The 4-byte data CP, CP , DDM and DDM are followed by 1-byte of data indicating the data type, composed e.g. by 2 bits indicating whether or not the file is a real-time file and 6 bits indicating whether the data is computer data in general, audio data or video data, this 1-byte data being in a quadruple format. It is noted that the aforementioned data DDM is used when the data recorded in the data/address signal region 4 is the programmable ROM (PROM) type data. The present invention is not limited to the above described embodiments, but may be changed in many ways without departing from the purpose of the invention. For example, the present invention may be easily applied to a disk-shaped recording medium on which signals may be recorded by three or more different kinds of physical changes. The number of bytes for one sector or that of the servo signal region or the data/address signal region may be selected otherwise than the numbers shown in the above embodiments.

Claims: A disk-shaped recorded medium (1) having circumferential tracks into which at least data signals (4b) and address signals (4a) are written in either a first format by a first kind of physical change of the medium or a second format by a second kind of physical change of the medium characterised in that at least some signals recorded in said first format and at least some signals recording in said second physical format are separated by one of alternating servo signal regions (3), in which pits for tracking (P A , P B ) are recorded at alternately offset positions with respect to the center of the track and pits for clock generation (P C ) are recorded at the center position of the track, as servo signals. A disk-shaped recording medium according to claim 1, wherein at least some signals recorded in said first format and at least some signals recorded in said second format are separated by an inserted unrecorded region (5c) sufficient to allow apparatus for reading said disk to switch between reading said first format and said second format when signals in both said first format and said second format occur between successive servo signal regions. A disk-shaped recording medium according to claim 1, wherein said servo signals and said address signals (4a) are recorded as projections and recesses as said first format and said data signals (4b) are recorded photo- magnetically as said second format. A disk-shaped recording medium according to claim 1, wherein said servo signal regions (3) have a length of 15 to 30 microns. A disk apparatus for at least reproducing a disk-shaped recording medium (1) according to any of claims 1-4, wherein the disk apparatus comprises a pickup (20) for reading out said signals recorded in said first and second formats, and means for switching (63) between said signals recorded in said first format and said signals recorded in said second format, said switching taking place in said servo signal region.

Inventors: OGAWA HIROSHI, SAKO YOICHIRO, OGAWA, HIROSHI, SAKO, YOICHIRO
Applicants: SONY CORP, SONY CORPORATION
Application year: 1987
Main classification: G11B20
IPC codes: G11B7, G11B21, G11B20