Optical recording medium

Abstract: An optical recording medium (10) provided with both a recordable area (2) in which data can be recorded and a read-only area (6) in which data has previously been recorded in an unerasable manner. In the recordable area, a guide groove is previously formed for tracking control, and recording may be performed, for example, photomagnetically, along the guide groove. In the read-only area, data is previously recorded by offsetting the groove or a land along the track in accordance with the data. This read-only data may be reproduced by detecting the laser light radiated from an optical pickup and reflected by the medium by a two-segment photodetector.

Description: This invention relates to an optical recording medium, such as a magneto-optical disc. More particularly, it relates to a recording medium of the type in which a recordable area, often called a RAM area, and a read-only or reproduce-only area, often called a ROM area, are provided on a single medium. An optical recording medium for data recording is known. For example, in a magneto-optical disc, a tracking guide groove or grooves are provided on the disc in the form of a spiral or concentric circles. Data is adapted to be recorded on or reproduced from the recording track along the track direction by taking advantage of the photomagnetic effects of the disc material, with the previously formed guide groove or grooves or the lands between the grooves used as the recording track. Data is recorded or reproduced photomagnetically under a tracking servo based on optical detection of the guide grooves. In such a case, addresses and data are recorded alternately on the recording track, and data control is achieved on the basis of this address data, so that data having a specific address can be recorded or reproduced on a block-by-block basis or a sector-by-sector basis. It would be convenient for users and producers of software if data which is only to be read and not rewritten, such as an operating system or a basic dictionary, could be supplied in a pre-recorded form on an otherwise recordable medium. For this reason, a recording medium, such as a disc or a card, has been developed on which a read-only area (a so-called ROM area) and a recordable area (a so called RAM area) are provided together. Figure 1 of the accompanying drawings shows an example of a magneto-optical disc as a recording medium on which the data which is only to be read is previously recorded. In this figure, a recordable, or RAM, area 2 on which signals can be recorded and read-only, or ROM, area 3 are provided on the magneto-optical disc 1. In the RAM area 2, the preformed guide grooves or lands between the guide grooves are used a the recording tracks 4 on which data is recorded photomagnetically. In the ROM area 3, tracks 5 are formed in which data which is only to be read is previously recorded by preformatting, for example, in the form of pits. JP-A-63 167 474, for example, also discloses an optical disc which has a ROM area and a RAM area. However, in such a magneto-optical disc 1, the signals received by the tracking servo at the time of scanning the ROM area 3 may be based on pits as, for example, in the method disclosed in US-A-3 876 842. Thus, since the tracking servo normally reproduces information from the RAM area 2 photomagnetically, the servo must be switching to cater for the different formats of the RAM area 2 and the ROM are 3. JP-A-62 043 839 discloses an optical disc in which information is recorded by modulating the information recording groove. EP-A-O 299 573 discloses an optical disk on which information may be optically recorded along a preformed track, the track further being "bi-phase" modulated in a radial direction (so that the track is offset laterally) to store additionally position information. Similarly, JP-A-63 032751 discloses a magneto-optic recording medium in which the groove for reading information is track-width modulated (so that the track varies in width) to store additionally header information. It is a principal object of the present invention to provide a recording medium having both a recordable area and a ready-only area, in which tracking by a servo may be performed in a uniform manner. According to the present invention there is provided an optical recording medium adapted for recorded data to be read therefrom by optical means, comprising: a first area in which data may be rewritably recorded along a previously formed read-write recording track 5; and a second area being read-only area in which data has been previously recorded, characterised in that the data in said second area has been recorded by offsetting portions of a read-only recording track in a direction lateral to the track direction as a function of the data recorded. It should be noted that the language used in the specification has been principally selected for readability and instructional purposes, and may not have been selected to delineate or circumscribe the inventive subject matter, resort to the claims being necessary to determine such inventive subject matter. The invention will be further described by way of non-limitative example with reference to the accompanying drawings, in which:- Figure 1 is a diagrammatic planar view showing an example of a conventional disc having a read-only area. Figure 2 is a diagrammatic planar view showing a magneto-optical disc according to an embodiment of the present invention. Figure 3 shows a typical example of a recording format of a read-only area of the disc. Figure 4 is a block circuit diagram showing a typical example of a recording/reproducing apparatus for illustrating the present invention. Figures 2 through 4 of the drawings depict various preferred embodiments of the present invention for purposes of illustration only. One skilled in the art will readily recognise from the following discussion that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the invention described herein. The preferred embodiment of the present invention is hereinafter explained by referring to the accompanying drawings. Referring to figure 2, a magneto-optical disk 10 has a transparent base plate on which a perpendicular magnetization film exhibiting magneto-optical effects is formed. The magneto-optical disk 10 is divided into, for example, a recordable area 2 (RAM area) on its outer periphery and a read-only area 6 (ROM area) on its inner periphery. On this magneto-optical disk 10, tracking guide grooves are provided in the form of a helix or of concentrical circles. In the RAM area 2, the inside of the groove or the land between the adjacent grooves is used as the recording track 4 on which data is to be recorded photo-magnetically. In the ROM area 6, tracks 7 are formed, in which the data which is only to be read is expressed in the form of lateral deviations or offsets of the tracks in the direction of the track width, i.e. by modulation along the track. The data in the form of offsets along the track is recorded at a frequency sufficiently high as compared with the tracking error signal frequency so as not to affect tracking error signals produced from the tracks 7. When the data which is only to be read is recorded in the ROM area 6 in the form of offsets along the track, tracking error detection in the ROM area with the aid of the guide grooves may be performed in the same way as in the RAM area 2. In this manner, even when track jumps should occur across the RAM area 2 and the ROM area 6, tracking may be performed continuously, so that stability of servo capturing is achieved with high response characteristics. A specific example of a recording format in the ROM area 6 for data which is only to be read is hereinafter explained by referring to Fig. 3. In the specific example of Fig. 3, a format similar to the format for a compact disk (CD) is used as the data recording format by offsetting along the track in the direction of the track width. In a customary CD format, each block or sector is a data recording unit formed by 98 frames from a 0'th to a 97th frame, with each frame being 588 times the channel clock frequency T or 588T. Recording areas for frame sync signals, sub codes and data including parity bits, are provided within each frame. At the leading end of each fame, 24T frame sync signals, formed by 24 channel bits, and 14T sub codes are connected to each other by 3T connecting bits. In the remaining 544T, 32 symbols or 32 bytes of sample data and parity data are provided after modulation by a so-called EFM or 8-14 modulation system. The frame sync signal is of a so-called out-of-rule pattern not found in the EFM system, and contains a succession of two 11T intervals between transitions. The 14T sub code area corresponds to one symbol. As data is recorded by offsetting along the track in the specific example of Fig. 3, sync signals are provided having the same format as that of the frame sync signal portion of the CD format. The sync signals consist of a succession of two 11T intervals between transitions, followed by successions of 7T, 11T (=7T + 4T) and 4T intervals between transitions, thereby constituting 44T of the leading portion of each frame inclusive of the above mentioned 22T frame sync pattern. These sync signals are used for synchronization of each frame as a unit. However, for synchronization of each sector constituted by a plurality of blocks, here 98, as a unit, the 8T at the terminal end of the leading 44T may be used as the sector or block mark for block synchronization. For example, the sector mark at the leading frame of a block of the so-called phase encoding system may be written in the sector mark at the leading frame as a "0," with a rise in signal level at the center of 8T, whereas a "1" may be written in the sector marks for the remaining frames, with a drop in signal level at the center of 8T, for distinguishing the frame at the leading end of the block from the remaining frames. In the remaining 544T (544 channel bit) data area, excluding the 44T sync area at the leading end of the frame, the read-only data is recorded by offsetting along the track with a period which is an integral multiple of the channel clock period T of the CD format, such as 8T, as the reference. In the example of Fig. 3, the PE system with a 1 bit slot equal to 8T is used as the modulation system for the offsetting or deviation along the track. However, when the clock period is an integral multiple of the channel clock period, a so-called biphase mark modulation system or the EFM or 8-14 modulation system may also be employed. When the recording along the track is performed by the above mentioned PE system with 1 bit of 8T, read-only data of 68 (i.e., 544/8) bits may be recorded in the above mentioned 544T data area. A concrete example of a recording/reproducing data signal on or from a magneto-optical disk, the recording medium in the ROM area of which the read-only data is recorded by an offsetting deviation along the track, is hereinafter explained by referring to Fig. 4. In this figure, the magneto-optical disk 10 has a RAM area and a ROM area, and is provided with a recording track or tracks in the spiral or concentric form. In the ROM area, data which is only to be read is recorded in the form of offsets along the track. The magneto-optical disk 10 is adapted to be driven rotationally at a constant linear velocity (CLV) or at a constant angular velocity (CAV) by a spindle motor 11. A laser beam from a laser light source 12, such as a laser diode, is collimated by a collimator lens 13 so as to be then irradiated on the magneto-optical disk 10 by means of a beam splitter 14 and a so-called biaxial object lens 15 for focusing and tracking. The reflected beam from the magneto-optical disk 10 is separated by the beam splitter 14 so as to be incident on a polarization beam splitter 17 by means of an optical system 16 such as a 1/2 wavelength plate, converging lens or a cylindrical lens. The reflected beam is separated in the polarization beam splitter 17 into a P-component and an S-component before being incident into photodetectors 18 and 19 adapted for detecting tracking error signals, focusing error signals and magneto-optical signals (MO signals). The outputs of the photo-detectors 18 and 19 are transmitted to a differential amplifier 20 to produce a difference for extracting photomagnetically recorded data signals or MO signals, with the output signal from the differential amplifier 20 being transmitted to an MO data reproducing circuit 21. The tracking error signals and the focusing error signals are detected with the aid of a four-segment type device in the light receiving section of the photodetector 18. During accessing of the ROM area, the read-only data, recorded as offsets along the track, may be produced from the high-frequency component of the tracking error signals and transmitted to a read-only data reproducing circuit 22 for data reproduction. The tracking error and focusing error signals are transmitted via servo control circuit 23 to a biaxial type object lens driving unit, not shown. In this manner, the data which is only to be read is previously recorded or pre-formatted in the ROM area of the disk by offsetting along the track, so that tracking control may be performed in a unified manner, and tracking control switching may be eliminated. On the other hand, it also becomes possible to prevent any adverse effects on tracking by recording the read-only data in the form of pits, while the response characteristics or stability of the tracking control operation at the time of track jumps across the RAM area and the ROM area may be improved. The recording media, such as optical disks, on which data which is only to be read is pre-formatted by the offsetting or deviation of the recording track itself, may be mass-produced easily by a press working process using a master disk or stamper at the time of disk production. From the above description, it will be apparent that the invention disclosed herein provides a novel and advantageous optical recording medium. The foregoing discussion discloses and describes merely exemplary methods and embodiments of the present invention. As will be understood by those familiar with the art, the invention may be embodied in other specific forms without departing from the essential characteristics thereof. For example, the present invention is not limited to the above mentioned embodiment and may be applied to various recording media, such as an organic dye optical disk, various write-once disks, overwrite disks, optical cards or magneto-optical cards, besides the magneto-optical disks. The RAM area may also be a programmable read-only area, also commonly known as a PROM area. Sync signals or address data may also be recorded in the recording tracks in the RAM area by track deviations or offsets along the track, while photomagnetic recording may also be made on the tracks in the ROM area. It is to be noted in addition that the recording format for data recorded by offsetting along the track is not limited to the specific example shown in Fig. 3. Accordingly, the disclosure of the present invention is intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following claims.

Claims: An optical recording medium (10) adapted for recorded data to be read therefrom by optical means, comprising: a first area (2) in which data may be rewritably recorded along a previously formed read-write recording track (4); and a second area (6) being read-only area in which data has been previously recorded, characterised in that the data in said second area has been recorded by offsetting portions of a read-only recording track (7) in a direction lateral to the track direction as a function of the data recorded. An optical recording medium according to claim 1, wherein the frequency of data recorded in the second area (6) by offsetting portions of the track (7) in a direction lateral to the track direction is selected to be distinguishably higher than the frequency of tracking error signals produced upon scanning the track (7). An optical recording medium according to claim 2, wherein a plurality of frame sync signals are formed in the second area by offsetting portions of the track (7) in a direction lateral to the track direction with a predetermined period between said frame sync signals. An optical recording medium according to claim 3, wherein a specified signal is formed at the end of said frame sync signal by offsetting a portion of the track (7) in a direction lateral to the track direction at an interval of a predetermined number of frames. An optical recording medium according to any one of claims 1 to 4, wherein data control data is previously formed by offsetting portions of the track (4) of said first area (2) in a direction lateral to the track direction. An optical recording medium according to any one of claims 1 to 5, wherein said optical recording medium is a magneto-optical disc (10). An optical recording medium according to any one of the preceding claims, wherein said read-write recording tracks (4) are defined in said first area (2) by a groove or grooves in said recording medium. An optical recording medium according to any one of the preceding claims, wherein the data in said first area (2) may be rewritably recorded photomagnetically.

Inventors: SAKO YOICHIRO, YAMAGAMI TAMOTSU, SAKO, YOICHIRO, YAMAGAMI, TAMOTSU
Applicants: SONY CORP, SONY CORPORATION
Application year: 1990
Main classification: G11B7
IPC codes: G11B13, G11B27, G11B11, G11B20, G11B7