Data recording apparatus and methods

Abstract: A disc (1) having recordable and recorded areas discretely scattered over it is formed with a guard band to prevent the recorded area from being destroyed by a track jump caused by an undue impact or vibration applied to the disc during a recording operation. Additionally, storing in memory (13) a predetermined amount of information from an edge of a recorded area before recording, the edge providing a boundary between the recorded area and a recordable area, allows recovery of data in the recorded area destroyed by a track jump caused by an undue impact or vibration applied to a disc.

Description: The present invention relates to recording methods and apparatus for recording data, such as music data, onto a disc recording medium for example. US Patent Application serial number 945488, filed 10 September 1992, for example, discloses a data-rewritable disc recording medium on which a user can record data such as music data and which is provided with a so-called user table of contents (UTOC) for managing the data, such as music data, in a recorded area and a recordable area. When recording a program, a recording apparatus searches the UTOC for a recordable area on the disc to record audio data to the area. It is known that random access operation is far easier with a disc recording medium such as a magneto-optical disc than with a tape recording medium such as a digital audio tape (DAT) or a compact cassette tape. Accordingly, one program need not always be recorded in a continuous segment. A segment herein denotes a part of one or more recording tracks in which physically continuous data is recorded. The data may be recorded in a single segment or a plurality of discrete segments. Therefore, even if tracks for recording a program are physically divided into a plurality of discrete segments, repeating a recording/reproducing operation on each segment with an associated high-speed access operation allows the program to be recorded or reproduced as an integral entity. For example, a recording arrangement as shown in Figure 1 of the accompanying drawings is possible where a first piece of music and a second piece of music are recorded respectively in a segment T1 and a segment T2 that are contiguous with each other, and fourth and fifth pieces of music are recorded in a divided fashion in segments T4(1) to T4(4) and segments T5(1) to T5(2) respectively, these segments being distributed over tracks. It should be noted that Figure 1 is a schematic diagram of a recording arrangement on a disc recording medium. Actually, a single segment often consists of a plurality of tracks formed spirally or concentrically. When recording and erasing of programs on a magneto-optical disc is repeated, the disc comes to contain both recorded segments and erased segments simultaneously. When overwriting a recorded program with another program which has a shorter music playing time for example, data remaining in a resultant differential area becomes meaningless as integral data. An area recorded with such fragmentary data is therefore registered in the above-mentioned UTOC as a recordable area. This prevents wasted data recording areas from being formed as a result of repeated recording and erasing operations. It should be noted here that data to be recorded includes not only music signals but also any other digital signals, and a block of the data which is continuous in its content and meaningful as an entity is hereinafter referred to as a program. It is apparent that, with the above-described disc medium, recording of a program is continued by accessing a plurality of segments which provide recordable areas for respective parts of the program, and, on reproduction, the segments are accessed so that the parts are read to be put together into the original continuous program. Information necessary for linking the segments and indicating the recordable areas is stored as UTOC information which is rewritten with each rewriting or erasing operation as mentioned above. A recording/reproducing apparatus is controlled so that it reads this UTOC information to perform a head access operation for a proper recording/reproducing operation. Any undue vibration or impact applied to the recording/reproducing apparatus may cause a track jump. For example, as shown in Figure 2 (a) of the accompanying drawings, if there are recorded areas (REAs) adjacent to both sides of a freely recordable area (FRA), a recording head (an optical head or a magnetic head) normally scans from address A1 to address A2. However, a track jump may throw the recording head out of the FRA into the adjacent REA as indicated by the dashed lines TJ in Figure 2 (b). The track jump may destroy recorded data, for example a portion indicated by DS in the figure, making the data irrecoverable. Therefore, if a track jump occurs, a recording operation which is under way must be immediately suspended (that is, laser power output or magnetic-field application must be turned off). A system for detection of a track jump is disclosed in US Patent number US-A-5012461 for example in which absolute-position information recorded on a disc as a pregroup (a wobbling group) is monitored for its continuity and a track jump is identified by detecting a discontinuity whereupon a recording operation which is under way is suspended. However, this system has a drawback in that, during the delay before information from reflected light coming from a pregroup is decoded as absolute-position information, a jump may have taken place over several tracks making prevention of data destruction impossible. That is, if a scanning operation is suspended based on the absolute-position information, it is often too late to protect data against destruction. In another approach, a traverse signal generated when a laser spot traverses a track is monitored to detect a track jump. While this method provides quick detection, in practice the traverse signal can be generated by foreign matter on the disc, for example, thereby falsely indicating a track jump. If a recording operation is suspended by a traverse signal generated by foreign matter on the disc, recording efficiency decreases, thereby reducing the practicality of apparatus based on such a detection method. This problem is especially conspicuous when dubbing a piece of music from a source equipment unit. According to the present invention there is provided recording apparatus as set forth in claim 1 and a re-recording method as set forth in claim 8. The invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a diagram illustrating a disc medium capable of recording one program in discrete segments; Figure 2 is a diagram illustrating a previously proposed recording operation; Figure 3 is a block diagram illustrating a recording/reproducing apparatus; Figure 4 is a diagram illustrating a data structure of UTOC information to be read into recording/reproducing apparatus; Figure 5 is a diagram illustrating a stage of segments controlled by corresponding table pointing data and parts tables; Figure 6 is a diagram illustrating a track structure of a recording medium; Figure 7 is a schematic diagram illustrating a track jump; Figure 8 is a schematic diagram illustrating a guard band; Figure 9 is a schematic diagram illustrating data rewriting; Figure 10 is a flowchart explaining a recording operation; Figure 11 is a flowchart explaining a recording operation; Figure 12 is a flowchart explaining a recording operation for writing a recording start position as an offset at re-recording; Figure 13 is a flowchart explaining a recording operation for overwriting a recording start position at re-recording in an embodiment of the invention; Figure 14 is a diagram illustrating a recording operation performed over a plurality of segments; and Figure 15 is a diagram illustrating a read pointer and a write pointer of a memory unit of an embodiment of the invention. First, the construction of a recording/reproducing apparatus will be described with reference to Fig. 3. Then, segment control data will be described which is written as UTOC information on a magneto-optical disc for use on the above-mentioned recording/reproducing apparatus with reference to Figs. 4 and 5. The arrangements to be described are implemented by a recording/reproducing apparatus for example which uses a magneto-optical disc as a recording medium. Fig. 3 is a block diagram of an essential portion of this recording/reproducing apparatus. Now, referring to Fig. 3, reference numeral 1 indicates a magneto-optical disc recorded with a plurality of programs (audio data) for example and rotationally driven by a spindle motor 2; and reference numeral 3 indicates an optical head for radiating a laser beam onto the magneto-optical disc 1 at a high-level output, in recording, for heating a recording track up to a Curie temperature or, in reproducing, at a low-level output for picking up data from a reflected light by magnetic Kerr effect. For this purpose, the optical head 3 has an optical system comprising a laser diode as laser output means, a polarization beam splitter, and an objective lens, and a detector for picking up the reflected light. The objective lens 3a is displaceably held by a two-axis mechanism 4 in directions radial and vertical to the disc. The optical head 3 in its entirety is adapted to move in the direction radial to the disc by means of a thread feed mechanism 5. Reference numeral 6 in the same figure indicates a magnetic head for applying a magnetic field modulated by supplied data onto the magneto-optical disc. The magnetic head 6 is opposed to the optical head 3 with the magneto-optical disc 1 in between. When a reproducing operation is performed, information detected by the optical head 3 from the magneto-optical disc 1 is fed to an RF amplifier 7. The RF amplifier 7 performs an arithmetic operation on the received information to extract a reproduced RF signal, a tracking error signal, a focus error signal, absolute-position information (recorded on the magneto-optical disc 1 as a pregroup (wobbling group)), address information, subcode information, and a focus monitor signal. The reproduced RF signal is fed to an encoder/decoder 8. The tracking error and focus error signals are fed to a servo circuit 9. The address information is fed to an address decoder 10 to be demodulated. The focus monitor signal is fed to a system controller 11 comprising a microcomputer for example. The servo circuit 9 generates servo drive signals based on the tracking error signal and the focus error signal, and a track jump instruction, a seek instruction, and rotational speed detected information coming from the system controller 11 to control the two-axis mechanism 4 and the thread feed mechanism 5, which in turn perform focus and tracking control, thereby controlling the spindle motor 2 to a constant angular velocity (CAV) or a constant linear velocity (CLV). The reproduced RF signal is fed to the encoder/decoder 8 to be subjected to such processing as EFM (Eight-Fourteen Modulation) demodulation and CIRC (Cross Interleave Reed-Solomon Coding) to be temporarily stored in a buffer RAM 13 by a memory controller 12. Reading of data by the optical head 3 from the magneto-optical disc 1 and transfer of the reproduced data from the optical head 3 to the buffer RAM 13 are performed at a rate of 1.41 Mbits/second. The data stored in the buffer RAM 13 is read at a timing so that the reproduced data is transferred at 0.3 Mbit/second. The read data is sent to an encoder/decoder 14 to be subjected to reproduced signal processing such decoding compacted sound. A resultant signal is converted by a D-A converter 15 into an analog signal to be fed to a predetermined amplifier via a terminal 16 for reproduced output. For example, the analog signal is output as left-channel and right-channel audio signals. The absolute-position information obtained by decoding the pregroup information or the address information recorded as data is fed from the address decoder 10 to the system controller 11 via the encoder/decoder 8 to be used for various control operations. A lock detect signal for a PLL (Phase Locked Loop) circuit for generating a bit clock for a recording/reproducing operation and a monitor signal for monitoring the reproduced data (for right and left channels) for a missing frame synchronization signal are also fed to the system controller 11. When recording the magneto-optical disc 1, a recording signal (an analog audio signal) applied to a terminal 17 is converted by an A-D converter 18 into a digital signal, which is fed to the encoder/decoder 14 to be encoded for sound compaction. The recording data thus compacted is temporarily stored in the buffer RAM 13 by the memory controller 12. The stored data is read at a predetermined timing to be fed to the encoder/decoder 8, where the data is subjected to encoding processing such as CIRC and EFM to be fed to a magnetic head driver 22. The magnetic head driver 22, based on the encoded recording data, feeds a magnetic head drive signal to the magnetic head 6 to make it apply a magnetic field having an N or S magnetic pole to the magneto-optical disc 1. At the same time, the system controller 11 sends a control signal to the optical head 3 to instruct it to output the laser beam of recording level. Reference numeral 19 indicates an operator panel comprising user operated keys. Reference numeral 20 indicates a display comprising a liquid crystal display for example. The keys on the operator panel 19 include a record key, a playback key, a stop key, a music select key, and search keys such as cue and review. Reference numeral 21 indicates a RAM for holding TOC (Table of Contents) information recorded on the magneto-optical disc 1. The RAM 21 is therefore hereinafter referred to as the TOC memory. Upon loading the magneto-optical disc 1 or immediately before starting a recording or reproducing operation, the system controller 11 drives the spindle motor 2 and the optical head 3 to extract data from a TOC area provided on inner most peripheral for example of the magneto-optical disc. The extracted TOC data is fed to the system controller 11 via the RF amplifier and the encoder/decoder 8 and is stored in the TOC memory 21 to be used for controlling recording/reproducing operations of the disc 1. Especially with a recordable disk medium such as one mentioned above, segment control data is recorded for allowing one program to be recorded/reproduced as one or more segments. That is, a user TOC area (hereinafter referred to as a UTOC) is provided whose contents can be rewritten according to recording or erasure of data for managing recording data areas. The UTOC has a data structure as shown in Fig. 4 for example. The UTOC consists of data areas of 4 bytes x 587 for example. It starts with a header having a synchronization pattern consisting of one-byte data of all 0's or all 1's, indicating that it is a UTOC. The UTOC also holds data such as a first program number recorded (a first TNO), a last program number recorded (a last TNO), sector usage, disc identification data at predetermined addresses respectively. Further, the UTOC prepares an area for recording corresponding table pointing data (P-DFA to P-TNO255) by which recorded programs are related to a control table to be described. The control table consists of 255 parts tables 01 to FF. Each parts table contains a start address and an end address providing a start and an end of an associated segment, mode information about the segment (or track), and, if the segment is linked to another segment, link information indicating a parts table recorded with a start address and an end address of the destination segment. The track mode information contains information whether the segment is overwrite-protected or duplication-protected, information whether the segment carries audio information, and information whether the recorded audio data is monaural or stereo. The link information specifies parts tables to be linked by using numbers (01 to FF) assigned to them. That is, in the control table, the parts tables correspond to the segments, one by one. For example, if a program is recorded in three discrete segments, their locations are managed by three corresponding parts tables linked together. Numbers (01 to FF) of these parts tables can be used for numbers of the associated segments. Each of the parts tables (01 to FF) in the control table indicates contents of its associated segment by corresponding table pointing data (P-DFA to P-TNO255). P-DFA (Pointer for a start address of a Defective Area) indicates a defective area on the magneto-optical disc 1 and specifies a start parts table of one or more parts tables indicating a defective track (or segment) caused by a scratch or the like. That is, if there is a defective segment, a corresponding segment number 01 to FF is recorded in the corresponding table pointing data P-DFA. In a corresponding parts table, the defective segment is specified by its start and end addresses. If there is another defective segment, it is indicated by a parts table pointed by link information of the first parts table. If there is no defective segment any more, link information of the second parts table is set to "00" for example, indicating that there is no further link. P-EMPTY (Pointer for an Empty slot on a parts table) indicates a start parts table of one or more unused parts table in the control table. If there is an unused parts table, one of 01 to FF is recorded as the corresponding table indicating data P-EMPTY. If there are more than one unused parts table, they are sequentially specified by link information from the parts table specified by the corresponding table pointing data P-EMPTY to link all the unused parts table in the control table. For example, with a magneto-optical disc recorded with no data and having no defect, none of the parts tables is used, so that a parts table 01 is specified by the corresponding table pointing data P-EMPTY, a parts table 02 is specified by link information of the parts table 01, a parts table 03 is specified by link information of the parts table 02, and so on until parts table FF is specified to be linked, by way of example. In this case, link information of the parts table FF is set to "00" to indicate that there is no link any further. P-FRA (Pointer to a start address of a Freely Recordable Area) indicates a data recordable area (including an erased area) on the magneto-optical disc 1 and specifies a start parts table of one or more parts tables respectively indicating a track (or segment) providing a recordable area. That is, if there is a recordable area, one of 01 to FF is recorded in the corresponding table pointing data P-FRA. In a corresponding parts table, a segment providing the recordable area is indicated by its start and end addresses. If there are more than one such a segment, that is, if there are more than one parts table, they. are sequentially linked by link information up to a parts table whose link information is set to "00". Fig. 5 schematically illustrates how segments providing recordable areas are managed. This indicates a state in which, if segments 03, 18, 1F, 2B, and E3 provide recordable areas, they are sequentially linked with the start segment 03 specified in the corresponding table pointing data P-FRA. The above-mentioned defective areas and unused parts tables are also managed in the same manner. P-TNO1 to P-TNO255 (Pointers for a start address of track n) indicate programs recorded on the magneto-optical disc 1 respectively. For example, the corresponding table pointing data P-TNO1 specifies a parts table which indicates a first segment in terms of time of one or more segments in which one piece of music, or one program, is recorded. If, for example, a program providing a first piece of music is recorded not divided over tracks, or if it is recorded in one segment, the recorded segment is specified by its start and end addresses held in a parts table pointed by the P-TN01. If, for example, a program providing a second piece of music is dividedly recorded in two or more discrete segments on the disc, these segments are specified in the order of recording time to indicate a recorded location of the program. That is, a parts table specified by the corresponding table pointing data P-TNO2 is linked by its link information to a second parts table which in turn is linked by its link information to a third parts table, and so on in the order of recording time up to a parts table whose link information is set to "00" (the same state as shown in Fig. 5). Thus, since all segments recorded with data constituting the second piece of music for example are sequentially stored, using the UTOC data allows the optical head 3 and the magnetic head 6 to access these discrete segments, reproducing the second piece of music or overwriting it efficiently. The recording/reproducing apparatus of a first arrangement (which is not an embodiment of the invention) on which the magneto-optical disc 1 recorded with the above-mentioned UTOC data manages the recordable areas on the disc by means of the UTOC data stored in the TOC memory 21 to control recording/reproducing operations. Especially, in recording, the UTOC data is searched for a recordable area on the disc and music data is recorded in it; if the recordable area is immediately preceded or followed by a recorded area, a guard band is provided on the recordable area at its front end and/or rear end to protect the adjacent recorded area from being overwritten. And, a criterion by which to determine an occurrence of a track jump during a recording operation is established according to a preset length of the guard band, executing a re-recording operation efficiently. First arrangement: Referring to Fig. 6, a recording track on the magneto-optical disc 1 is made up of contiguous clusters. Each cluster CL consists of a sub data area made up of four sectors (one sector = 2,352 bytes) and a main data area made up of 32 sectors. Data is recorded on a cluster basis. One cluster is equivalent to two to three tracks. An address is recorded on a sector basis. Now, as shown in Fig. 8, suppose a case in which a segment specified by address A1 and address A2 consisting of clusters CL1 through CL9 for example provides a freely recordable area FRA and the FRA is adjacently preceded and followed by recorded areas respectively. The addresses A1 and A2 are stored as start and end addresses respectively in a parts table (or another parts table linking thereto by its link information) specified by corresponding table pointing data P-FRA as UTOC data. In this arrangement, a recording operation is performed so that a guard band GB is formed on the freely recordable area FRA at a portion adjacent to the recorded area REA in a length equal to one cluster. To be specific, the system controller 11 performs an operation to shift an address indicating a recording start location from the start address A1 to an address A3 by one cluster and an address indicating recording end address from the end address A2 back to an address A4 by one cluster, thus setting a recordable area. Consequently, the recording head scans between addresses A3 and A4 as indicated by H1 in Fig. 9. Therefore, clusters CL1 and CL9 provide guard bands respectively in which no data will be recorded. The system controller 11 detects an occurrence of a track jump by detecting a traverse signal generated in the servo circuit 9. Since the traverse signal is caused every time a laser spot traverses a track, counting the number of traverse signals allows to determine how many tracks have been traversed. It should be noted, however, that a traverse signal may be also caused by a foreign matter on the disc, such as a dust. The system controller counts the number of traverse signals and, having detected a track jump over three or more tracks as shown in Fig. 7 (a), determines an occurrence of a track jump, immediately suspending the recording operation. Then, if possible, the system controller 11 performs a re-recording operation. The system controller can perform a re-recording operation if a track jump TJ has occurred in the recordable area as indicated by scan H4 or H5 of Fig. 8 for example. If one or two traverse signals are detected singularly as shown in Fig. 7 (b), the system controller regards that they have been caused by a dust on the disc for example, continuing the recording operation. Even if one or two traverse signals singularly detected have been caused by an actual track jump over one or two tracks, scanning by the recording head will not reach the recorded area REA beyond the guard band GB as indicated by H2 or H3 of Fig. 8 because the guard band consists of one cluster (for two to three tracks). Therefore, such a track jump will not lead to a destruction of recorded data. Whether an actual track jump or a false track jump has occurred is accurately determined by checking continuity of absolute-position information recorded as a pregroup on the disc. If an actual track jump is determined, re-recording is performed. Fig. 10 is a flowchart describing the recording processing by the system controller 11 which performs the above-mentioned recording operation control. Steps in the flowchart are indicated by F101 through F123. When the magneto-optical disc 1 is loaded, the system controller 11 reads the TOC information into the TOC memory 21 as mentioned above. Therefore the UTOC data is also stored in the TOC memory. The system controller 11 executes a routine of Fig. 10 by using the stored UTOC data when a recording operation is instructed on the operator panel 19 for example. First, the system controller 11 searches a parts table specified in the corresponding table pointing data P-FRA in the UTOC data for start and end addresses of a freely recordable area FRA (F101 and F102). Then, the system controller determines whether a segment length (that is, the end address minus the start address) of the freely recordable area FRA is greater than double the guard band length (that is, greater than two clusters) (F103). If the segment length is equal to or smaller than double the guard band length, the system controller determines that the FRA is unrecordable and searches a next parts table directly linked to the current parts table for start and end addresses to calculate its segment length. That is, a freely recordable area FRA whose segment length is greater than double the guard band length is found in steps F101 through F103. The obtained FRA provides an area in which data is recorded. When the FRA to be recorded has been specified, the system controller 11 shifts the FRA's start address A1 forward to the address A3 by the guard band length (one cluster) and establishes the address A3 as the actual recording start address (F104). At the same time, the system controller shifts the FRA's end address A2 back to the address A4 by the guard band length (one cluster) and establishes the address A4 as the actual recording end address (F105). When the actual recording start and end addresses have been established, the system controller 11 positions the recording head to the recording start address A3 to start recording data from it (F106, F107, and F108). That is, a recording scan starts as indicated by H1 of Fig. 8, thus recording the data fed to the recording head via the buffer RAM 13. During the recording scan, the system controller 11 monitors whether the head position has reached the recording end address A4, a track jump over three tracks or more has been detected by checking a traverse signal, and a discontinuity has been detected in the absolute-position information obtained from the pregroup on the disc (F109, F110, and F111). If the head position has reached the recording end address A4 with no traverse signal for three tracks or more and no discontinuity in the absolute-position information detected, the system controller determines that the recording operation on that segment has completed normally and terminates the recording operation (F109 to F122). Thus, this FRA has become a recorded area REA. Accordingly, the system controller 11 changes corresponding data in the UTOC data and rewrites the UTOC data area on the disc (F123). As described with reference to Fig. 1, since the magneto-optical disc for use on this arrangement allows data (for example, a program) to be dividedly recorded in two or more segments, the system controller 11 continues the recording operation by accessing a next freely recordable area FRA2 upon completion of the recording on the first FRA1 as indicated by H6 of Fig. 14. In this case, too, data is recorded on the FRA2 between addresses A3 and A4 so that guard bands are formed as described above. The system controller rewrites the UTOC data collectively upon completion of the recording on one segment or all of multiple segments (freely recordable areas). During data recording on the freely recordable area FRA, the system controller 11 monitors an occurrence of a traverse signal. If a detected traverse signal is for one or two tracks, the system controller continues the recording operation by ignoring the traverse signal. If the detected traverse signal is for three or more tracks, the system controller regards it as an occurrence of a track jump and immediately suspends the recording operation to prevent a data destruction (F110 to F112). Since it is possible that a data destruction has already occurred upon detection of the track jump, the system controller performs re-recording if the destroyed at can be recovered. Especially with this arrangement, the guard band GB prevents the recording head from getting out of the freely recordable area FRA being recorded if a jump over three tracks or more occurs. Therefore, in most cases, the destroyed data can be recovered by data remaining in the buffer RAM 13. It is apparent that suspending the recording will not destroy data three tracks or more away from a point at which the track jump occurred. Consequently, the system controller first detects absolute-position information generated after a track jump (F113) and, based on the information, determines whether the track jump occurred toward an inner peripheral of the disc or toward an outer peripheral (F114). If the track jump is found happening toward the inner peripheral of the disc, from cluster CL7 to cluster CL5, as indicated by scan H4 of Fig. 8 for example, it is regarded that a data destruction occurred starting with a cluster (CL4 or CL5) having a sector immediately before a sector containing the read absolute-position information; therefore, the system controller obtains that cluster (CL4 or CL5) (F115). On the other hand, if the track jump is found happening toward the outer peripheral of the disc, from cluster CL7 to cluster CL5 as indicated by scan H5 of Fig. 8 for example, it is regarded that the data recording error occurred starting with a cluster (CL3) having a sector containing absolute-position information detected last before the track jump occurred. Therefore, the system controller obtains that cluster (CL3). Meanwhile, even if a detected traverse signal indicates that only one or two tracks have been traversed, a recording error or a data destruction may have happened actually in a freely recordable area FRA being recorded (as indicated by H2 or H3 of Fig. 8 for example). Therefore, the system controller monitors associated absolute-position information for any discontinuity as mentioned above. If a discontinuity is found, the system controller regards it that a track jump has occurred and suspends the recording operation (F111 to F117). The system controller then obtains a cluster with which to start a re-recording operation for data recovery-or error correction (F118). This cluster is a cluster CL containing an address immediately before a point at which the discontinuity of absolute-position information was detected or a cluster CL containing an address immediately before an address at which the discontinuity was detected, whichever is nearer the inner peripheral of the disc. When the cluster to be re-recorded has been obtained in F115, F116, or F118, the system controller checks the buffer RAM 13 for the data recorded between that cluster and the cluster in which the track jump occurred inclusive. If the data is not found, data recovery is impossible, so that the system controller terminates the recording processing as a recording error (F120). If the data is found stored, the system controller sets a start address of the obtained cluster as a recording start address and restarts the data recording operation with that cluster (F121 to F106). Thus, by means of the above-mentioned processing, the freely recordable area FRA is formed with the guard band GB for data recording and, even if a possibility of a track jump which is prevented by the guard band from causing the recording head to jump to another area for a recording error has been detected, the system controller does not immediately determine it to be a track jump. Rather, the system controller continues the record operation until it detects the discontinuity in absolute-position information to confirm the occurrence of the track jump. That is, a traverse signal generated by a foreign matter such as a dust on the disc will not suspend the recording operation. If a track jump occurs, the system controller immediately performs a data recovery operation to continue the recording operation. It is apparent that, with the processing described by the flowchart of Fig. 10, all freely recordable areas to be recorded are formed with the guard band GB respectively; actually, however, those freely recordable areas having no immediately adjacent recorded areas need not always be provided with the guard band. Rather, it is preferable for such freely recordable areas not to have the guard band in order to leave more data recording space in them. Consequently, it is preferable that processing from F101 to F105 of Fig. 10 be replaced by processing from F201 to F217 of Fig. 11. To be specific, when a freely recordable area FRA has been found at starting a recording operation (F210, F202), the system controller determines whether areas adjacently preceding and following the FRA respectively are recorded areas REA's (F230). If both REA's are found recorded, the system controller determines whether a segment length of each REA is greater than double (equivalent to two clusters) the guard band length as shown in Fig. 10 (F204). If the segment length is found greater, the system controller determines that each REA is recordable and turns on flags FF and FR (F205). If either of areas adjacent to the obtained freely recordable area FRA is not recorded area REA, the system controller determines which one is recorded (F206). Since the guard band may be provided on the FRA only at one end thereof, the system controller determines whether its segment length is greater than the guard band length (equivalent to one cluster) (F207). If the segment length is found greater, the system controller determines the area to be recordable and determines whether the area is before or after the FRA (F208). If the area is found before the FRA, the system controller turns on the flag FF and turns off the flag FR (F209); if the area is found after the FRA, the system controller turns off the flag FF and turns on the flag FR (F210). If neither of the areas are found recorded areas, no guard band need be provided. In this case, the system controller determines these areas to be recordable and turns off the flags FF and FR (F211). When the flag FF is on, the system controller adds the guard band length to the start address A1 to provide the recording start address A3 (F212 to F213). When the flag FF is off, the start address A1 is used as the recording start address without change (F212 to F214). In this case, the guard band is not formed on the freely recordable area FRA at its front end. When the flag FR is on, the system controller subtracts the guard band length from the end address A2 to provide the recording end address A4 so that the guard band is formed on the FRA at its rear end (F215 to F216). When the flag FR is off, the end address A2 is used as the recording end address without change (F215 to F217). In this case, the guard band is not formed on the FRA at its rear end. Subsequently, the processing proceeds to step F106 of Fig. 10 where the above-mentioned operation is performed, realizing effective usage of recordable areas. It is apparent that variations may be made to this arrangement. For example, the guard band may be provided only at either of the front end or the rear end of a recordable area regardless of whether the areas adjacent thereto are recorded areas or not. Although, in this embodiment, the occurrence of a track jump is determined when a traverse signal generated over three or more tracks has been detected, the number of tracks depends on the guard band length and therefore, if the guard band is longer than that used in this arrangement, a track jump may be determined by a traverse signal generated over four or more tracks for example. This is because a traverse signal generated over the number of tracks that does not cause the recording head to jump out of a segment being recorded may be regarded, for the time being, as a detection error caused by a foreign matter such as a dust on the disc to continue the recording operation without destroying data recorded in other areas. Thus, setting the guard band length and the track jump detection level in a correlated relation enhances accuracy and speed of the track jump detection for preventing data destruction, securely preventing recorded data from being destroyed. Second arrangement: The present invention provides a recording method which does not use the guard band used on the first arrangement in recordable areas. An embodiment of such a method will be described below as a second arrangement, which comprises a preferred embodiment of the invention. As mentioned in the description of the first arrangement, even a small track jump generated over one or two tracks may have destroyed recorded data. However, storing a predetermined amount (one cluster for example) of data of an immediately adjacent recorded area before starting a recording operation allows destroyed data to be recovered by performing a re-recording operation. By detecting a track jump in the same manner as with the first arrangement, this setup can prevent an irrecoverable destruction of recorded data from happening and enhance recording efficiency. In the second arrangement, the system controller 11, when recording data, searches UTOC data for a recordable area on the disc and records the data to the area. If a recorded area is adjacently located before the recordable area, the system controller reads recorded data from a predetermined location in the recorded area and stores the read data in the buffer RAM 13 before starting a recording operation on the recordable area. If a track jump occurs during the recording operation, destroying data in the adjacent recorded area, the system controller writes the stored data on the recorded area for data recovery. It should be noted that a location at which a data write operation for data recovery starts is not set in the area where the data destruction occurred; rather, the data write operation starts from a beginning of the recordable area to write the data recorded there all over again and continues into the recorded area to write the stored data. This second arrangement will be described below by referring to several drawings. It is supposed, as shown in Fig. 9, that a segment (at addresses AWS to AWE) containing clusters CL1 through CL9 is a freely recordable area FRA and it is immediately preceded and followed by a recorded area REA respectively, by way of example. The addresses AWS and AWE are stored as start and end addresses in a parts table specified in corresponding table pointing data P-FRA as UTOC data (or they are stored in another parts table linked from that parts table by link information). In the second arrangement, the system controller, before starting a recording operation, reads data recorded in one cluster for example in the recorded area REA at and end adjacent to the freely recordable area FRA. To be specific, the system controller 11 first obtains an address one cluster before the recording start address AWS to make the obtained address a past data read start address APS and then causes the recording/reproducing head (comprising the optical head 3 and a magnetic head 6) to perform a reproducing scan starting with the address APS, starting a recording scan when the recording/reproducing head has reached the recording start address AWS. These scans are indicated by H1 of Fig. 9. In the figure, a hatched portion represents the reproducing scan while a non-hatched portion the recording scan. The system controller 11 detects an occurrence of a track jump by detecting a traverse signal generated in the servo circuit 9. Since the traverse signal is caused every time a laser spot traverses a track, counting the number of traverse signals allows to determine how many tracks have been traversed. It should be noted, however, that a traverse signal may be caused by a foreign matter such as a dust on the disc.The system controller counts the number of traverse signals and, having detected a track jump over three or more tracks as shown in Fig. 7 (a), determines an occurrence of a track jump, immediately suspending the recording operation. Therefore, there is little possibility that data recorded before these three or more is destroyed. Even if the data is destroyed, the stored data for one cluster (equivalent to two to three tracks) can be used to record the data again for data recovery. If one or two traverse signals are detected singularly as shown in Fig. 7 (b), the system controller regards that they have been caused by a dust on the disc for example, and does not suspend the recording operation immediately because of the detection. Rather, the system controller subsequently confirms-associated absolute-position information recorded as a pregroup on the disc and checks the absolute-position information for a discontinuity. If the discontinuity is found, the system controller determines that a track jump has occurred. Even if one or two traverse signals singularly detected have been caused by an actual track jump over one or two tracks, destroying recorded data for one to two tracks until confirmation of the track jump by absolute-position information, the past recorded data for one cluster can be recovered because it has been stored in advance. Fig. 12 is a flowchart describing the recording processing by the system controller 11 which performs the above-mentioned recording operation control. The steps in the flowchart are indicated by F301 through F333 respectively. Following registers are provided for the address management for controlling a recording/reproducing head scan position on the disc and for the read/write control on the buffer RAM 13: AWS for a disc writing start address, or an address indicating a location at which a current write operation starts (= a start address in a recordable area); AWE for a disc writing end address, or an address indicating a location at which the write operation terminates (= an end address in a recordable area); APS for a past data reading start address, or an address at which a past data reading operation starts; APE for a past data reading end address, or an address indicating a last position of a past data reading range; AW for a disc writing address, or an address indicating a location at which a disc writing operation starts (this address is updated by re-writing or the like); AWC for a current writing address, or an address indicating a location being currently written; ATJ for an address immediately after track jump detection, or an address detected immediately after a track jump; ARW for disc rewriting address, or an address indicating a start location for rewriting after a track jump; PR for a read pointer, or a pointer for specifying a buffer RAM reading address; and PW for a write pointer, or a pointer for specifying a buffer RAM writing address. When the magneto-optical disc 1 is loaded, the TOC information is read as mentioned above and therefore the UTOC data shown in Fig. 4 is stored in the TOC memory 21. The system controller 11 executes a routine of Fig. 12 by using the stored UTOC data when a recording operation is instructed on the operator panel 19 for example. First, the system controller 11 searches a parts table specified in the corresponding table pointing data P-FRA in the UTOC data for start and end addresses of a freely recordable area FRA and makes the start address a disc writing start address AWS and the end address a disc writing end address AWE (F301). Then, the system controller determines whether an area immediately before the FRA is a recorded area REA or not. If the area immediately before the freely recordable area FRA to be recorded is a recorded area REA as shown in Fig. 9, the system controller obtains a location one cluster (M) before the disc writing start address AWS and makes the location a past data reading start address APS (F303). Then, the system controller positions the recording/reproducing head to the APS (F304, F305). The system controller sets the disc writing start address AWS to the past data reading end address APE (F306) and the disc writing start address AWS to the disc writing address AW (F307) to read the data recorded on the disc from the past data reading start address APS into the buffer RAM 13 (F308). It should be noted that buffer RAM read and write operations are controlled by the write pointer PW and the read pointer PR respectively whose addresses are specified in a storage area of the buffer RAM 13 as shown in Fig. 15 (a) to be updated to next address locations respectively every time a read operation and a write operation take place. When these addresses have reached final locations respectively, they return to their start locations. The past data read after step F308 is sequentially stored in the buffer RAM 13 at locations specified by the write pointer PW. When a reproducing scan is continued until it reaches the past data reading end address APE (that is, it matches the writing address AW in this case) for example, the past data is stored in the buffer RAM 13 as shown in Fig. 15 (b). If the area before the freely recordable area is found other than a recorded area REA, the past data need not be read, so that the system controller sets a disc inner most peripheral address to the past data reading end address APE (F309) and the disc writing start address AWS to the disc writing address AW (F310) to position the recording/reproducing head to the disc writing address AW directly (F311). It should be noted that the disc inner most peripheral address is set to the APE to be used for a comparison operation-of step F322 to be described. When the recording/reproducing head has reached the disc writing address AW because of a scan for reproducing past data or because of a direct access, the system controller terminates a past data reading operation if it has been done (F312) and stores input data fed from the terminal 17 into the buffer RAM 13 (F313). The system controller then reads the input data stored in the buffer RAM 13 and supplies it to the magnetic head 6 to start writing it to the disc 1 (this is a write operation to be executed this time) (F314). The data supplied from the terminal 17 and put through sound compaction processing to be recorded this time is stored in the buffer RAM 13 subsequent to the past data by the write pointer PW as shown in Fig. 15 (c). To supply the data to be recorded this time to the magnetic head 6, the read pointer PR has been set at starting a read operation to an address next to the area recorded with the past data to read the input data at a predetermined timing. Subsequently, a recording scan is performed from the disc writing start address AWS to the disc writing end address AWE as indicated by H1 of Fig. 9 to record the data from the magnetic head 6 to the disc 1. During this recording scan, the system controller 11 captures a location currently being scanned as the current writing address ACW and monitors whether the head position has reached the recording end address AWE (that is, ACW = AWE) and a track jump has been detected (F315, F316, and F317). It should be noted that , as mentioned earlier, a track jump is detected by checking a traverse signal for an occurrence of an track jump over three or more tracks or by checking absolute-position information obtained from the pregroup on the disc for a discontinuity. If the head position has reached the recording end address AWE without detecting any track jump, the system controller determines that the recording operation on that segment has terminated normally to terminate the operation (F316 to F331). That is, because this freely recordable area FRA has been made a recorded area REA, the system controller accordingly changes the associated data in the UTOC data to rewrite the UTOC area on the disc (F331) and terminates the disc writing operation (F332). As described with reference to Fig. 1, since the magneto-optical disc allows data (for example, a program) to be dividedly recorded in two or more segments, the system controller 11 continues the recording operation by accessing the following freely recordable area FRA2 upon completion of the recording on the first FRA1 (for example, an access from cluster CL9 to cluster CL10). In this case, too, the system controller starts a write operation on a next recordable area FRA by first reading past data of a recorded area REA if the REA is adjacently located before the FRA. The system controller rewrites the UTOC data collectively upon completion of the recording on one segment or all of multiple segments (freely recordable areas). If the system controller 11 has detected an occurrence of a track jump during recording data to the freely recordable area FRA, it immediately suspends the recording operation to prevent data destruction (F317 to F318). Since it is possible that a data destruction has been caused by a track jump before it is detected, the system controller tries to recover the destroyed data by means of re-recording. To be specific, the system controller first obtains absolute-position information provided after the track jump, sets it to the address ATJ provided immediately after the track jump (F319), and determines, based on the absolute-position information, whether the track jump has taken place toward the inner peripheral or the outer peripheral of the disc (F320). That is, the address ATJ is compared with the current writing address ACW. Basic data may be destroyed by a track jump over less than three tracks (a track jump over three or more tracks instantaneously suspends a recording operation to prevent a data destruction from happening). A track jump toward the inner peripheral of the disc which may lead to a data destruction is classified into one of two types; a track jump that has reached a recorded area (cluster CL0) as indicated by scan H2 of Fig. 9 and a track jump that has taken place in a recordable area FRA as indicated by scan H6. If ATJ < ACW and the track jump has taken place toward the inner peripheral, it is possible that the data destruction has started from a cluster containing a sector before a sector which provides the ATJ, so that an address of a start sector of the cluster is made the disc rewriting address ARW (F321). The system controller then compares the disc rewriting address ARW with the past data reading end address APE to determine whether the recording/reproducing head has reached the recorded area REA or not (F322). If the head is found having reached the recorded area REA as indicated by H2, the system controller reads the data of the destroyed cluster CL0 (that is, the cluster specified by the past data reading start address APS and the past data reading end address APE) from the buffer RAM 13 to rewrite the cluster. The rewriting is performed in one of two methods. In one method, the rewriting starts at the APS, a location for starting past data reading as indicated by H3 of Fig. 9. In the other method, the rewriting starts at CL1 (AWS) as indicated by H5 of Fig. 9. The rewriting according to the first method will be described by the flowchart of Fig. 13. The steps of the flow are represented by F401 through F433 respectively. Since the flowchart of Fig. 14 is almost the same as the flowchart of Fig. 13, descriptions of common steps are omitted. To perform the rewriting according to the first method, the system controller sets the disc writing address AW for rewriting to the past data reading start address APS (F423). Consequently, if a track jump indicated by H2 occurs, the rewriting starts from the past data reading start address APS as with H3, followed by the current data recording that starts at cluster CL1. If a track jump indicated by H6 occurs, the rewriting is performed starting at cluster CL3 as with H7 for example. In the second method, as indicated by H5, the rewriting for data recovery of cluster CL0 starts at cluster CL1, which occupies a head position of the freely recordable area FRA. When the data of the destroyed cluster CL0 has been recovered in cluster CL1 as indicated by DP in Fig. 9, data DC to be currently recorded is recorded again starting at cluster CL2. Thus, if a track jump over less than three tracks occurs again during rewriting, the optical head will not reach cluster CL(-1) where data recovery is impossible. Execution of the second method will be described again by referring to the flowchart of Fig. 12. The above-mentioned processing has been up to step F322 inclusive. The following will describe processing of F323 and on. When the system controller determines that a track jump has occurred toward the inner peripheral of the disc, destroying the recorded area, the controller sets the disc writing start address AWS to the disc writing address AW (F323). If the track jump has occurred within the freely recordable area FRA as indicated by H6, rewriting may be performed starting from a location at which the track jump has occurred, or the disc rewriting address ARW (cluster CL3) obtained in step F321, so that the system controller sets the disc rewriting address ARW to the disc writing address AW (F324). Then, the system controller obtains a data range (an address range on the disc) currently stored in the buffer RAM 13 from the write pointer PW and the read pointer PR (F325) to check if data in the range for rewriting, or data between the disc writing address AW and an address immediately before the track jump (= the current writing address ACW) still remains in the buffer RAM 13 (F333). If the data is found missing, the rewriting is impossible, so that the system controller terminates the recording operation with a write error (F333). Usually, however, a rewriting operation is enabled because a track jump over three or more tracks suspends the recording operation instantaneously and at least the data of two tracks including the past data of the recorded area REA remain in the buffer RAM 13. Subsequently, the system controller sets the read pointer PR in the buffer RAM 13 to a data location corresponding to the disc writing address AW from which to start rewriting (F329) and positions the recording/reproducing head to the disc writing address AW (F330) to restart writing the data starting from the disc writing address AW (F330 to F312 through F317). Accordingly, if a track jump as indicated by H2 has occurred, writing of the past data DP restarts at the disc writing start address AWS (cluster CL1) and writing of the current data DC restarts at cluster CL2 as indicated by H5. If a track jump as indicated by H6 has occurred, the writing restarts at cluster CL3 for example as indicated by H7. The above-mentioned second method is advantageous over the first method as follows. For example, if a track jump occurs again while a recording operation for data recovery is being performed in the first method as indicated by H4 of Fig. 9, the recording head may further reach cluster CL(-1) to destroy the past data recorded there. Since the past data of this cluster CL(1) has not been stored beforehand, recovery of the data is impossible. On the contrary, the second method does not involve such a problem because the recording start position has been offset. If, in step F320, a track jump toward the outer peripheral of the disc is detected as indicated by H8 of Fig. 9 for example, it is possible that an error has occurred in data recording starting at an address detected last before the occurrence of the track jump, or a sector providing the current writing address ACW, the system controller obtains a cluster containing that sector and makes an address of a start sector of that cluster the disc rewriting address ARW (F327). Then, the system controller sets the disc rewriting address ARW to the disc writing address AW (F328) and proceeds to step F329 to restart the recording operation. Therefore, in this case, the writing restarts at cluster CL4 as indicated by H9 for example.Meanwhile, as indicated by H5, when the past data of cluster CL0 is moved to another area (cluster CL1) for example, the cluster CL0 becomes a recordable area. Cluster CL1 recorded with the past data of cluster CL0 becomes a recorded area containing data continued from cluster CL(-1). Consequently, after performing such a rewrite operation, required data is rewritten in the UTOC so that a link is provided between cluster CL(-1) and cluster CL1, and cluster CL0 is managed as a recordable area. That is, a parts table which indicates cluster CL0 as a recordable area is provided. Thus, the above-mentioned processing described by referring to Fig. 10 ensures data recovery and continuation of a recording operation immediately after a data destruction caused by a track jump in a recordable area FRA or a track jump reaching a recorded area REA, preventing an eventual data destruction. Since data up to a predetermined track is recoverable, a track jump can surely be detected by checking a traverse signal and/or checking absolute-position information for discontinuity. A recording operation need not be suspended if a traverse signal has been generated by a foreign matter such as a dust on the disc for example. Thus, the recording efficiency is enhanced remarkably. Additionally, if past data has been destroyed, an area recorded with the destroyed data is not rewritten; rather, the past data before destruction is written again to a freely recordable area FRA, preventing a destruction of data in an irrecoverable area if a track jump occurs again during the rewriting. It should be noted that, in the above-mentioned first and second arrangements, an amount of past data to be stored in the buffer RAM 13 is not restricted to one cluster. It may be set to other amounts depending on a storage size of the buffer RAM 13 or a track jump detection method used. In these arrangements, only data of a recorded area adjacently located before a freely recordable area FRA is stored beforehand. It is also possible, if an area adjacently located after an freely recordable area FRA is a recorded area REA, to previously store data of a start cluster for example of the area REA in order to prevent a data destruction caused by a track jump toward the outer peripheral of the disc. It is apparent that, although the above-mentioned first and second arrangements are implemented by a recording/reproducing apparatus for example, they may be a recording-only apparatus. It is also apparent that the present invention may be embodied in any recording apparatus compatible with not only a magneto-optical disc but also a writable optical disc. It will of course be appreciated that various other changes and variations may be made without departing from the scope of the invention as defined in the appended claims.

Claims: Recording apparatus for recording data onto a recording medium (1) having a recordable area and a recorded area simultaneously, said recorded area and said recordable area comprising either one continuous segment respectively or a plurality of discrete segments respectively, said recording medium (1) further having a control table containing a start address and an end address of said segment or each of said plurality of segments and link information for linking said plurality of segments if said recorded area and said recordable area comprise said plurality of segments, the recording apparatus comprising: recording/reproducing means (3) for recording data onto the recording medium (1) and reading data from the recording medium (1); storing means (13) for storing recording data entered at data recording for a predetermined duration; and control means (11) for controlling read/write operations at a recording/reproducing position by said recording/reproducing means (3) and read/write operations in said storing means (13) such that a determination is made, before data is written to a recordable area, whether a segment adjacent to a segment of the recordable area is or is not a recorded area and, if the segment adjacent to the segment of the recordable area is determined to be a recorded area, then at least part of data in the segment of said recorded area is stored in said storing means (13) in order to prevent data destruction, and said entered data is recorded via said storing means (13) when said recording/reproducing means (3) has reached the start address of the segment of said recorable area Recording apparatus as claimed in claim 1, wherein said control means (11) suspends a data recording operation if a track jump is detected during recording data onto a recordable area and, if data in said recorded area adjacent to the recordable area is destroyed by the track jump, reads from said storing means (13) the data in said recorded area previously stored in said storing means (13) to recover the data in said destroyed recorded area by using said data read from said storing means. Recording apparatus as claimed in claim 1, wherein, if said recorded area is located before said recordable area, data is read from said recorded area in a portion between a predetermined location near a trailing end of said recorded area and the trailing end to be stored in said storing means (13). Recording apparatus as claimed in claim 1, wherein, if said recorded area is located after said recordable area, data is read from said recorded area in a portion between a beginning of said recorded area and a predetermined location away from the beginning to be stored in said storing means (13). Recording apparatus as claimed in claim 1, wherein, if said recorded area is located before and after said recordable area respectively, both the data between the predetermined location near the trailing end of said recorded area before said recordable area and the trailing end and the data between the beginning of the said recorded area after said recordable area and the predetermined location away from the beginning are read to be stored in said storing means (13). Recording apparatus as claimed in claim 3, wherein, if data in said recorded area adjacent to a recordable area has been destroyed by a track jump, said control means reads the data of said recorded area previously stored in said storing means (13) to record the data from the start address of said recordable area and subsequently record the entered recording data stored in said storing means. Recording apparatus as claimed in claim 6, wherein, if a recording operation for recovering the data in said destroyed recorded area has been executed, said control means (11) registers in a control table the recorded area on the recording medium (1) in which the data stored in said storing means (13) was originally recorded as a recordable area. A re-recording method for an apparatus for recording data onto a recording medium (1) having a recordable area and a recorded area simultaneously, said recorded area and said recordable area comprising either one continuous segment respectively or a plurality of discrete segments respectively, said recording medium further having a control table containing a start address and an end address of said segment or each of said plurality of segments and link information for linking said plurality of segments if said recorded area and said recordable area comprise said plurality of segments, the method comprising the steps of: setting a writing start address and a writing end address of a recordable area on the recording medium (1) based on said control table data; determining whether an area before said writing start address is a recorded area; subtracting, if the area before said writing start address has been determined to be a recorded area, a predetermined length from said writing start address and storing a result of said subtraction as a past data reading start address for reading data of a predetermined length from said recorded area; positioning an optical pickup (3) to said past data reading start address; setting a past data reading end address to said writing start address; writing data into storing means (13) based on said past data reading start address and said past data reading end address; and storing, when said past data reading end address has been reached, entered data into said storing means (13) and writing the data from said storing means to the recordable area. A re-recording method as claimed in claim 8, comprising the steps of: detecting whether a track jump has taken place during a recording operation; suspending, if the track jump has been detected, the recording operation; storing an address immediately after the track jump; determining whether the track jump has taken place toward an inner periphery of the recording medium; calculating, if the track jump has been found taking place toward the inner periphery, a recording unit containing an address immediately before said stored address immediately after the track jump to store the calculated recording unit as a rewriting address; comparing said rewriting address with said past data end address; and determining, if said rewriting address has been found smaller than said past data end address, that a data destruction has taken place to set said past data start address to a rewriting start address to record the past data stored in said storing means. A re-recording method as claimed in claim 8, comprising the steps of: detecting whether a track jump has taken place during a recording operation; suspending, if the track jump has been detected, the recording operation; storing an address immediately after the track jump; determining whether the track jump has taken place toward an inner periphery of the recording medium; calculating, if the track jump has been found taking place toward the inner periphery, a recording unit containing an address immediately before said stored address immediately after the track jump to store the calculated recording unit as a rewriting address; comparing said rewriting address with said past data end address; and determining, if said rewriting address has been found smaller than said past data end address, that a data destruction has taken place to set a rewriting start address to a writing start address of the recordable area to record the past data stored in said storing means.

Inventors: OKABE MASANOBU, OKABE, MASANOBU, Okabe, Masanobu, c/o I.P.D., L. &amp; I. Prop. Dpt
Applicants: SONY CORP, SONY CORPORATION
Application year: 1993
Main classification: G11B19
IPC codes: G11B19, G11B27, G11B11, G11B7