Abstract:
A storage medium stores information on a plurality of tracks formed thereon, each of the tracks being divided into a plurality of sectors. The storage medium includes a physically formed sector beginning identifier provided at a leading portion of each sector, and an information storing portion. The information storing portion, another sector address portion at the trailing end of the information storing portion, includes at least one sector address portion at a leading end of the information storing portion, another sector address portion at the trailing end of the information storing portion, and a data portion provided between the two sector address portions.

Description:
FIELD OF THE INVENTION 
     The present invention relates to improvements to a storage medium which increase the storage capacity of the medium. More particularly, the present invention relates to a storage medium in which sector address information is recorded using MSR techniques. 
     BACKGROUND OF THE INVENTION 
     Optical disks are widely used as external storage media for computers. Magneto-optical disks have become popular because they are rewritable and provide a relatively high recording density. In the past, 3.5 inch magneto-optical disks were only capable of storing 128 MB of information. Recent advances, however, have enhanced the storage capacity of 3.5 inch magneto-optical disks to 1.3 GB, and even greater increases in storage capacity are presently being sought. 
     Magneto-optical disks include at least one recording layer formed on a substrate. Information is recorded/reproduced from magneto-optical disks using a laser light source and a magnetic source. Typically, grooves (tracking guide grooves) are formed in spiral fashion on the substrate of the medium. Data is recorded on tracks provided on lands between these grooves. 
     In the past, the recording density of magneto-optical disks has been limited by the diameter of the beam spot of the laser beam. However, in recent years, magneto-optical super resolution technology known as MSR (Magnetically Induced Super Resolution) has facilitated the recording and retrieving of a mark smaller than the diameter of a laser beam. For example, with a 3.5 inch magneto-optical disk, recording and retrieving of a mark smaller than the laser beam spot with track pitch of 0.90 μm and a mark length of 0.38 μm is now possible. Consequently, a ten fold increase in storage capacity to 1.3 GB has been realized. 
     Magneto-optical disks record and retrieve in a storage unit termed a sector. By manner of illustration, FIGS. 12A and 12B show a traditional MSR magneto-optical disk sector format in which sector address information portion  90  is physically formed as an indented (embossed) pit with a stamper in the same manner as a tracking groove. Sector address information  90  includes a sector mark SM which indicates the beginning of a sector, PLL phase lead-in term signal VFO 1 , address mark AM indicating the beginning of the first sector ID, first sector address ID 1 , PLL phase lead-in term signal VFO 2 , address mark AM indicating the beginning of the second sector, second sector address ID 2  and post amble PA indicating the end of the sector address information portion. 
     Sector address information stored in ID 1  and ID 2  includes track number and sector number information. The second sector address ID 2  stores the same information as the first sector address, and is included as a backup in case ID 1  becomes unreadable. 
     A gap  91  separates the sector address information portion  90  from VFO area  92  in which a VFO pattern for adjusting the frequency is recorded. Sync byte area  93  is interposed between a data area  94 , and the aforementioned VFO area  92 . A post amble (PA)  95  and buffer  96  for a buffering area are formed subsequent the data area  94 . 
     Data is recorded at a high density in the data area  94  portion using MSR techniques. In contrast, sector address information portion  90  is recorded at a significantly lower density than the data recorded in the data portion  94 , since it is physically formed by embossing or the like. 
     Accordingly, one problem associated with conventional magneto-optical storage mediums relates to the relatively large area required to store sector address information, and the ensuant decrease in usable storage capacity of the medium. 
     OBJECTS 
     One object of the present invention is to increase the usable storage capacity of a magneto-optical storage medium by reducing the area required to store sector address information. 
     Another object of the invention is provide a storage medium including an error correction code for correcting a sector address. 
     Another object of the invention is to provide an improved method for determining whether a head is in an off track condition during a read operation. 
     Yet another object of the invention is to provide an improved method for verifying that a write operation has written to the correct sector, where the target sector is not read prior to the writing operation. 
     SUMMARY 
     Briefly, the present invention relates to an improved storage medium for storing information. Information is stored on a plurality of tracks formed on the storage medium, each of the tracks being divided into a plurality of sectors. Each sector includes a physically formed sector beginning identifier provided at a leading portion of the sector, and an information storing portion. At least one sector address portion for storing a sector address is provided at a leading end of the information storing portion, and a data portion for storing user data is provided after the sector address portion. 
     These and other aspects of the invention will be more fully understood by referring to the following detailed description and the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A and 1B are block diagrams of a first embodiment of a sector format of the present invention; 
     FIG. 2 is a drawing illustrating the principles of MSR recording and retrieving techniques used to record information on a magneto-optical disk of the present invention; 
     FIGS.  3 (A)-( 3 (E) illustrate steps in retrieving MSR information; 
     FIG. 4 is a block diagram of a variation of the sector format of FIG. 1; 
     FIGS. 5 and 6 are block diagrams of an optical disk device used to record/retrieve information to/from an optical disk embodying the sector format of the present invention; 
     FIGS. 7 and 8 are flow diagrams showing steps for writing data on a target sector; 
     FIG. 9 is a diagram showing positioning of the head during a data write operation; 
     FIG. 10 is a diagram showing positioning of the head during a write verifying action; 
     FIG. 11 is a flow diagram showing steps for verifying a write operation by performing a read operation; and 
     FIGS. 12A and 12B are block diagrams of a conventional sector format. 
    
    
     DETAILED DESCRIPTION 
     A first embodiment of the present invention will be explained with reference to FIGS. 1-3, in which FIGS. 1A and 1B are block diagrams of a sector format, and FIGS. 2 and 3 show principles of MSR recording and retrieving. 
     As FIG. 1A shows, a sector  1  according to the present invention which includes, in the order specified, a sector start identifier  10 , a PLL lead-in signal (VFO)  11 , sync bytes  12 , a data field  13 , a post-amble (PA)  14 , and a buffer  15 . 
     The sector start identifier  10  is a sector mark which indicates the beginning of a sector, and is a physically formed indented pit. The pLL lead-in signal (VFO)  11 , the sync bytes  12 , the data field  13 , the post-amble (PA)  14  and the buffer  15  are formed using MSR recording techniques which will be discussed later. The buffer  15  is a buffering area provided for absorbing rotational jitter of a spindle motor. 
     The data field  13  includes a sector track number (not specifically shown), a first sector address (ID 1 )  16  which contains a sector number, a 2048 byte data area  17 , a second sector address (ID 2 )  18  which contains the same information as the first sector address (ID 1 ), a CRC (Cyclic Redundancy Check) byte  19 , and an ECC (Error Correction Code) byte  20 . 
     The sector addresses (ID 1 )  16  and (ID 2 )  18  each contain four bytes. The CRC byte  19  is created by a commonly known method using the first sector address  16 , the data of 2048 byte data area  17  and the second sector address  18 . Also, the ECC byte  20  is created with a commonly known method using the first sector address  16 , the data of 2048 byte data area  17 , the second sector address  18  and the CRC byte  19 . 
     According to one aspect of the present invention, the sector addresses  16  and  18  are recorded using MSR techniques having a significantly higher recording density than the density of the physically formed sector start identifier  10 . Consequently, there is a reduction in the amount of physically formed sector address information. As a result, the overall storage capacity increases because more area is available to record user data. In fact, sector address information according to the present embodiment requires only 55 bytes, which is half of what is required in conventional storage media. In this manner, the present embodiment facilitates a 3% increase in storage capacity over conventional storage mediums using 110 bytes of physically formed sector address information. 
     Moreover, the use of MSR techniques to record the sector addresses  16  and  18  eliminates the need to provide the VFO 1 , AM, VFO 2  and AM pits of sector address information  90  (FIG. 12) provided in conventional devices. Accordingly, storage capacity in a device according to the present invention is further increased. 
     As noted above, sector start identifier  10  is formed as a physically indented pit. The use of a physically formed pit is desirable in order to assure detection of the beginning of a sector. 
     With the improved sector formatting of the present invention, the sector addresses ID 1   16  and ID 2   18  are recorded in the data field  13  using MSR techniques. As is well known in the art, misreading of the sector address may be determined using the CRC byte. Thus, if necessary, the misread sector address may be corrected using the ECC byte  20 . Consequently, accurate reading of sector addresses in a device according to the present invention is assured. 
     Still further, the detection of an off tracking error in the center portion of a sector is facilitated in the present invention using the sector addresses  16  and  18  provided on either side of the data area  17 . Specifically, an off tracking error is signaled if the sector address  16  which proceeds the data portion  17  does not match the sector address  18  which immediately follows the data portion  17 . 
     MSR recording and retrieving according to the present invention will be explained with reference to FIGS. 2 and 3. As shown in FIG. 2, a magneto-optical disk according to the present invention is provided with a magnetic recording layer  3  which includes a recording layer  6 , an intermediate layer  5  and a retrieving layer  4 . 
     The intermediate layer  5  has a property whereby it selectively passes signals recorded on the recording layer  6  to the retrieving layer  4 . Specifically, the intermediate layer  5  passes signals to the retrieving layer  4  only when heated to a predetermined constant temperature, e.g., 200° C. These signals are reproduced from the retrieving area while a read/record magnetic field having orientation A (FIG. 2) is applied. By carefully controlling the laser light source, only a small portion of the beam spot reaches the predetermined constant temperature. In this manner, it is possible to assuredly record and reproduce bytes recorded in an area smaller than the beam spot. The specific layer type for preferred Double Mask RAD technology but other types of the MSR technologies can be used. 
     FIGS. 3A through 3E illustrate principles of reproducing information using MSR techniques. In FIG. 3A a beam spot  2  does not encompass a portion P of the magnetic recording layer  3 . Accordingly, the portion P of the intermediate layer  5  will not pass any signals to the retrieving layer  4  because it is below the predetermined constant temperature. In FIG. 3B, the beam spot  2  has advanced and begins to heat portion P of the magnetic recording layer  3 . However, the intermediate layer  5  will not pass signals to the retrieving layer  4  because it is still below the predetermined constant temperature. In FIG. 3C, the beam spot  2  has advanced slightly and has heated portion P to the predetermined constant temperature. Consequently, the intermediate layer  5  will pass signals recorded in portion P to the retrieving layer  4 . This selective passing phenomenon is called a switched connection. 
     When the beam spot  2  advances as shown in FIG. 3D, the portion P of the intermediate layer  5  exceeds the predetermined constant temperature and ceases to pass (imprint/copy) signals to the retrieving layer  4 . Subsequently, as shown in FIG. 3E, the beam spot  2  passes the portion P, thereby allowing that portion to cool. In this manner, a mark which is less than the diameter of the beam spot of a light beam can be reproduced. 
     Recording of data using MSR techniques is a two step process involving a preliminary step of orienting a direction of the magnetic area of the recording layer  6  in a predetermined direction, and a final step of recording information. The orienting step involves scanning a portion of the magnetic area of the recording layer  6  with a beam spot  2  having an erasing intensity while applying a magnetic field oriented in an erase direction. As shown in FIG. 2, the ERASE magnetic field B is oriented in an opposite direction from the READ/RECORD magnetic field A. Moreover, the erasing intensity of the beam spot  2  is higher than the read intensity of the beam spot. 
     Recording of information is accomplished by applying a magnetic field oriented in a read/record direction while irradiating a light beam of a write intensity. The magnetic orientation of the byte heated to the predetermined temperatures changes from an initial erase orientation to the orientation specified by the READ/RECORD magnetic field A. 
     FIG. 4 is a block diagram of a variation on the sector format shown in FIGS. 1A and 1B. Notably, the position of the second sector address (ID 2 )  18  is shifted to follow the ECC byte  20 . As described above, off tracking of the head after the first sector address (ID 1 )  16  has been read is accomplished by comparing the first sector address (ID 1 )  16  with the second sector address (ID 2 )  18 . According to the second embodiment, the ability to detect off tracking of the head is enhanced to include off tracking during reproduction of the CRC  19  and the ECC  20 . 
     FIG. 5 is a block diagram of an optical disk device according to the present invention and FIG. 6 is a circuit diagram of the optical disk device of FIG. 5. A magneto-optical disk device  7  is connected to a host  9  as is shown in FIG. 5. A controller  45  includes an interface (not shown in the drawing) which exchanges commands and data with the host  9 , a microprocessor (MPU)  34  and an optical disk controller (ODC)  35 . The MPU  34  performs over-all control of the magneto-optical disk device, and the ODC  35  will be explained later with FIG.  6 . 
     A bias magnet  31  applies a magnetic field to a magneto-optical disk  30 . A bias magnet control circuit  36  controls the magnetic field of the bias magnet  31  in response to instructions from the MPU  34 . 
     A WRITE (recording) circuit  38  includes a WRITE modulator  42  and a laser diode control circuit  41 . The WRITE modulator  42  modulates WRITE data from the ODC  35  into data formatted in pit position modulation (PPM) record data (also called mark record) or into pulse width modulation (PWM) record data (also called edge record) corresponding to the type of magneto-optical disk. The laser diode control circuit  41  controls a laser beam intensity of an optical head  33  with this modulated data. 
     A READ (retrieve) circuit  40 , is equipped with an AGC (automatic gain control) circuit, a filter, a sector mark detection circuit, an analog/digital conversion circuit (ADC), a READ demodulator  43 , and a frequency synthesizer  44 . The frequency synthesizer  44  generates a READ clock signal. The READ demodulator  43  detects the sector mark from the pit signal or from MO signal input from the optical head  33 , and outputs a detection signal SM to the ODC  35 . The READ demodulator  43  also converts the MO signal input from the optical head  33  into a digital value and outputs it to the ODC  35 . 
     The optical head  33  detects the feedback light of the magneto-optical disk  30 , and inputs an ID signal/MO signal to the READ circuit  40 . A spindle motor  32  rotationally drives the magneto-optical disk  30 , and a spindle motor control circuit  39  controls the spindle motor  32  in response to directives of the MPU  34 . 
     A servo control circuit  37  has a TES detection circuit, a FES detection circuit, and a DSP (digital signal processor). The TES detection circuit creates a TES signal (tracking error signal) from light detected by the optical head  33 . Correspondingly, a FES detection circuit creates a FES signal (focus error signal) from light detected by the optical head  33 . The DSP drives a track actuator of the optical head  33  using the TES signal with a track servo loop, and drives a focus actuator of optical head  33  from the FES signal with a focus servo loop. Moreover, the DSP also drives and controls a VCM (which is not depicted in the drawing) which moves the optical head  33  in a direction crossing tracks of the magneto-optical disk  30 . 
     Turning now to FIG. 6, the ODC  35  is provided with a sync byte detection circuit  50 , a demodulation circuit  51 , a CRC check/ECC correction circuit  52 , a sector address verifier  53 , and a data buffer  55 . The MO signal digitized from READ circuit  43  is input to the sync byte detection circuit  50  and the demodulation circuit  51 . 
     A read process is performed by transmitting a data start signal to the demodulation circuit  51  when the sync byte detection circuit  50  detects sync bytes  12  (FIG.  1 ). Thereafter, the demodulation circuit  51  begins demodulation. However, if the sync byte  12  is not detected within a predetermined time interval, a sync byte undetected error is reported to the MPU  34  from sync byte detection circuit  50 . 
     Data demodulated by demodulation circuit  51  is sent to the CRC check/ECC correction circuit  52 . The CRC check/ECC correction circuit  52  calculates CRC bytes from the demodulated data, and compares the calculated CRC bytes with the CRC bytes  19  of the demodulated data. If they do not match, error correction is performed by the ECC byte  20  in the ECC correction circuit  52  to correct the data. If ECC correction is unsuccessful, an ECC correction error is sent to the MPU  34 . In this manner, an optical disk device  7  according to the present invention can assuredly obtain valid sector addresses even if the sector addresses are written using MSR techniques. 
     Restored data (or correct data which does not require correction) is sent to the sector address verifier  53  and the data buffer  55 . The sector address verifier  53  extracts the first sector address  16  and the second address  18  of a sector and compares them. If these two addresses match, it can be confirmed that the head was not off track while writing, and the confirmed sector address is posted to the MPU  34 . Conversely, an off tracking error is reported to the MPU  34  when the two sector addresses  16  and  18  do not match. 
     The above-described aspects of the present invention are not limited to magneto-optical disks, and may also be applied to other types of optical disks such as magnetic expansion retrieving type disks and magnetic field modulation type disks. In other words, the above-described aspects are applicable to other optical disks which record sector addresses with the same recording method as data. Furthermore, because it is contemplated that the present invention can be implemented for both a hard disk that magnetically controls the tracking and/or a hard disk drive that controls tracking with a laser unit, other implementations are within the scope of the present invention. 
     Write processing in a device according to the present invention will now be explained with reference to FIGS. 7 and 8. In step (S1), the MPU  34  verifies whether or not a WRITE command has been received. In step (S2), the WRITE command has been received, and the MPU  34  positions the head  33  twenty sectors ahead of the intended WRITE sector a (see FIG.  9 ). 
     The magnetization direction of the bias magnet  31  is oriented in step (S3-a) in the erase direction B (FIG.  2 ). In step (S3-b), the MPU  34  counts start sector identifiers  10  until the target sector a is reached, and erase processing is initiated in step (S3-c). It should be noted that the head cannot read the sector address at this time since the bias magnet  31  is oriented in the erase direction B. However, since the sector identifier  10  is formed as a physical pit, the head can detect (and count) the start of a sector irrespective of the magnetization direction of the bias magnet  31 . 
     In step (S4-a), the magnetization direction of the bias magnet  31  is oriented in the READ/RECORD direction A, the head  33  is once again positioned twenty sectors ahead of the target sector a (S4-b), and the MPU  34  counts start sector identifiers  10  until the target sector is reached (S4-c). Once the target sector is reached, write processing is initiated (S5). 
     It should be appreciated that the aforementioned erase and write operations were performed by counting down to the target sector, without actually verifying the sector address. Consequently, in steps (S6-S12), a verification process is performed to determine whether the write operation was performed on the intended sector to ensure that the write operation did not inadvertently operate on an adjacent track due to the head  33  being off track. 
     The verifying operation begins by positioning the head in sector c on the physical track which immediately precedes the target track (S6). See FIG.  10 . In step (S7-a), the head  33  reads from sector c (on the track which physically precedes the target track) until sector d (on the target track) which immediately precedes the target sector a. It should be noted that the tracks shown in FIG. 10 are formed in a spiral manner. 
     If an error is detected during the reading operation in step (S7-b), then it is likely the head was off track during either the erasing (S3-c) or writing (S5) operations, whereupon the MPU  34  reports a WRITE command abnormal termination  8  to the host and terminates further processing. In step (S8), if no read error is detected, the MPU  34  stores the sector address of sector d. Subsequently, in step (S9-a), the target sector a is read. As was explained above with reference to FIG. 6, the MPU  34  compares the first sector address  16  and the second sector address  18  of the intended sector to determine whether they match (S9-b). If the sector addresses do not match then an off track error has occurred and the MPU  34  reports a write command abnormal termination to the host  5  and terminates further processing. 
     In step (S10), the head reads from sector e which immediately follows the target sector. Then, in step (S11), the addresses of the sectors immediately preceding (sector d) and immediately following (sector e) are compared with the target address (sector a). If the relationship d&lt;a&lt;e is satisfied then processing continues with step (S12-a). Otherwise, an error is reported to the host  9 . 
     Next, in step (S12-a) a reading operation is performed from sector (e) (on the target track) until sector f (on the track which immediately follows the target track). Again, it should be noted that the tracks shown in FIG. 10 are formed in a spiral manner. 
     If an error is detected during the reading operation (S12-b), then it is likely that the head  33  was off track during either the erasing (S3-c) or writing (S5) operations, whereupon the MPU  34  signals a write command abnormal termination to the host  9  and terminates further processing. Conversely, if no read error is detected, the MPU  34  posts a WRITE command normal termination to the host  9  and terminates (S13). 
     In this manner, the MPU  34  can detect errors such as off track erasing and off track writing. Likewise, using the write verify operation (S6-S12), the MPU  34  is able to verify that data has been correctly recorded on the target sector even though it cannot verify sector addresses in real-time. The reading operation in steps S7a through S12b is able to detect off track conditions of the head in a track direction by checking a sector continuity of the sectors d, a, e, and also off track conditions in track traverse direction by checking read error from the sector c to the sector d and from the sector e to the sector f, that is, checking a sector continuity from the sector c to the sector f and whether c&lt;a&lt;f. 
     Read processing in a device according to the present invention will now be explained with reference to FIG.  11 . The MPU  34  verifies whether or not a READ command has been received (S20). Once the MPU  34  receives a READ command, it positions the bias magnet  31  in the READ direction (S21-a), and positions head  33  at sector b which is twenty sectors ahead of the intended read sector a (S21-b). See FIG.  9 . 
     Next, the MPU  34  counts sector identifiers  10 , until it reaches sector d, which immediately precedes the target sector (S21-c), and reads and stores the address of sector d (S22). The target sector a is then read (S23-a). As explained above, with reference to FIG. 6, the MPU  34  compares the first sector address  16  and the second sector address of the intended sector to ascertain whether they match (S23-b). Again, as explained earlier, if the sector addresses do not match then an off track error has occurred, and the MPU  34  reports a READ command abnormal termination to the host  9  and terminates. 
     The head  33  then reads the sector address of sector e, which immediately follows the target sector a (S24). The MPU then compares the sector address of sector e with the target sector address and the stored address of sector d (S25). If the relationship d&lt;a&lt;e is satisfied then the READ data in data buffer  55  is transmitted to the host  9  and a READ command normal termination is posted to the host (S26). Otherwise, an error has likely occurred during writing processing, and a READ command abnormal termination is reported to the host  9 . 
     Although a preferred embodiment of the storage medium has been specifically described and illustrated, it is to be understood that variations or alternative embodiments apparent to those skilled in the art are within the scope of this invention. Since many such variations may be made, it is to be understood that within the scope of the following claims, this invention may be practiced otherwise than specifically described.