Abstract:
A recording/playback apparatus, includes a supplying device for supplying continuous data at a predetermined transfer rate. A recording device having a certain seek performance and recording mode records the continuous data on the recording medium in a recording unit, and a first setting device sets the size of the recording unit according to the transfer rate of the supplied continuous data or the seek performance of the recording device or the recording mode. The recording device includes a designating device for designating the transfer rate according to the recording mode. The apparatus further comprises a second setting device for setting the number of allowable retries to play back data from said recording medium according to the transfer rate or the seek performance or the recording unit size.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a recording/playback apparatus, a recording/playback method and a presentation medium. In particular, the present invention relates to a recording/playback apparatus capable of recording and playing back data with a high degree of efficiency by modifying the number of retries. 
     Data recorded or played back by a hard disc drive (abbreviated hereafter to an HDD) is controlled by a file v management function of an operating system (abbreviated hereafter to an OS) which runs on a host computer. For example, the HDD is not aware of a location or a free area into which data is to be recorded, so that, in a recording operation, data is written into a location specified by the host computer. In a playback operation, on the other hand, data recorded on a disc is read out from a location specified by the host computer. 
     In the case of such an OS as MS-DOS™ and UNIX™, a recording area of a disc is divided into data blocks or sectors each having a fixed size of 512 or 1,024 bytes during initialization. Data is recorded in data-block units. This method is referred to as a fixed-size division method. 
     In the case of the fixed-size division method, when a disc is initialized, a sector specific number, which is also referred to as a sector ID, is written into the beginning of a sector. A sector ID represents a physical location on a disc. Typically, a sector ID comprises an 8-bit sector number, a 16-bit track number, an 8-bit surface number and a 16-bit error-inspection code which is referred to hereafter as a CRC (Cyclic Redundancy Check) code. 
     The host computer controls sector IDs as a series of logical block addresses (LBAs). In an operation to record data, the host computer specifies an LBA representing a physical location on the disc into which the data is to be written. 
     FIG. 10 is a block diagram showing a typical configuration of the related art HDD. Assume that MS-DOS is used as an OS in this typical configuration. In the HDD  1 , a microprocessor unit (abbreviated hereafter to an MPU, Micro Processing Unit)  11  controls all functions of the HDD  1 . A servo circuit  12  generates a driving signal for controlling a voice coil motor (abbreviated hereafter to VCM)  13 . The VCM  13  moves a magnetic head (not shown) to a predetermined track position on a disc  18 . A buffer  16  is used for storing data received from an external source and data to be supplied to an external destination. A read/write channel processing unit  17  carries out processing to generate a signal to be recorded onto the disc  18  and processing to play back a signal read out from the disc  18 . Controlled by the MPU  11 , a hard-disc controller (abbreviated hereafter to an HDC)  15  controls operations to write and read out data into and from the buffer  16  and exchanges data with the R/W channel processing unit  17 . The MPU  11 , the servo circuit  12 , the HDC  15  and the R/W channel processing unit  17  are connected to each other by an MPU bus  14 . 
     ECCs (Error Correction Codes) are added to data to be recorded onto the disc  18 . When an ECC error is detected for a sector in an operation to play back data from the sector, the MPU  11  issues a command to repeat the operation to read out data from the sector. This repeated operation is called as a retry. In an ordinary HDD, a number of retries are allowed and performed internally. 
     In a case where data can not be read out correctly from a sector, even if a number of allowable retries have been carried out, the MPU  11  treats the sector as a defective sector. In a following operation to write data into a defective sector, the data is written into a sector in an alternate area. This is called alternative-sector processing. 
     The HDD  1  is connected to the host computer  2  by a bus, such as an SCSI (Small Computer System Interface) bus or an IDE (Intelligent Drive Electronics) bus. 
     In the host computer  2 , MS-DOS is used as an OS  21 . A disc driver  22  is a program which allows the disc  18  to be accessed as a block device. A logical format program  23  is a program for writing necessary initialization information such as sector IDs and a file management table during initialization of the disc  18 . Linked to the device driver  22  and the logical format program  23 , a BIOS (Basic Input Output System)  24  renders I/O (Input/Output) services for inputting and outputting data from and to the HDD  1 . The BIOS  24  can be regarded as a collection of routine programs dependent on hardware. 
     When data having a high rate such as AV (audio/video) data is recorded or edited on the HDD  1  in logical block units, the continuous data is scattered over the disc into small pieces of data. The scattering of data is known as fragmentation. When fragmented data is read out from a disc, the read operation frequently enters a wait state due to head seeks and disk revolutions to read target positions, breaking the continuity of the output data. 
     In order to solve this problem, data is recorded not in logical block units, but in cluster units each comprising several block units. Typically, the size of a cluster unit is 1,024 sectors. The size of a cluster unit is set at such a value that the continuity of output data in a playback operation is sustained, even if the data recorded on the disc is fragmented into cluster units. 
     The size of a cluster is made uniform for all data types in order to make operations to write and read out data easy to control. Typically, the size of a cluster is set at an extremely small value which is obtained with regular data such as text data taken as a reference. If the size of a cluster is too small, however, data recorded on the disc is prone to fragmentation described above. If a small amount of data is recorded in large cluster units, an excessively large recording area will be wasted. 
     The size of a cluster can also be determined from a simple proportional relation with a reference data transfer rate or an assumed transfer-channel count. In this case, however, the size of a cluster is not optimum. In addition, the type of data and the number of transfer channels are not reflected in an upper limit of the number of retries that can be carried out in the event of an error detected in a data recording or playback operation. As a result, the transfer rate is not guaranteed for data with a strict continuity requirement such as AV data. 
     OBJECTS OF THE INVENTION 
     It is thus an object of the present invention to provide a recording/playback apparatus and a recording/playback method wherein the number of retry operations is determined in accordance with the size of each of units in which data is written and/or read out so that the data can be recorded and/or played back with a high degree of efficiency without losing data continuity. 
     SUMMARY OF THE INVENTION 
     In order to attain the above objects, according to a first aspect of the present invention, there is provided recording/playback apparatus, a recording/playback method and a presentation medium. The apparatus comprises a supplying device for supplying the continuous data at a predetermined transfer rate, a recording device having a certain seek performance and recording mode for recording the continuous data on the recording medium in recording unit, and a first setting device for setting the size of the recording unit according to the transfer rate of the supplied continuous data. The first setting device sets the size of the recording unit according to the seek performance of the recording device. The recording device includes a designating device for designating the transfer rate according to recording mode. The first setting device includes a device for setting the recording unit size according to the recording mode. The apparatus further comprises a second setting device for setting the number of allowable retries according to the transfer rate. The apparatus further comprises a second setting device for setting the number of allowable retries according to the seek performance. The apparatus further comprises a second setting device for setting the number of allowable retries according to the recording unit size. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the invention, reference is made to the following description and accompanying drawings, in which: 
     FIG. 1 is a block diagram showing a typical configuration of a host computer to which the present invention is applied; 
     FIG. 2 is a diagram showing the state of a transfer of AV data from a HDD to a host computer; 
     FIG. 3 is a diagram showing a typical structure of a data management format of a recording area in the HDD; 
     FIG. 4 is a diagram showing a layout of clusters of AV data with sizes varying in dependence on the recording mode; 
     FIG. 5 is a diagram showing relations between the number of channels to be transferred and the cluster size of transferred data with the number of allowable retries taken as a parameter; 
     FIG. 6 is a diagram showing relations between the number of channels and the required size of a buffer with the number of allowable retries taken as a parameter; 
     FIG. 7 shows a flowchart representing processing to play back data from a system-management area when a host computer is activated; 
     FIG. 8 shows a flowchart representing operations carried out by the host computer to record AV data; 
     FIG. 9 shows a flowchart representing operations carried out by the host computer to play back AV data; and 
     FIG. 10 is a block diagram showing a typical configuration of the related art recording/playback apparatus. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following is a detailed description of embodiments of the present invention with reference to the drawings. FIG. 1 is a block diagram showing a typical configuration of a host computer  1  to which the present invention is applied. It should be noted that recorded or playback data is AV data conforming to the MPEG (Moving Picture Experts Group) system. 
     An MPU  31  employed in the host computer  2  controls and coordinates all operations as well as executes file management of user data. The MPU  31  includes an embedded RAM (Random-Access Memory)  40  for storing data to be used temporarily such as a table showing newly found defective recording areas as well as necessary information on file management. On the other hand, a host RAM  32  is used for storing data such as a file-management table including a defect list  41  used in defect processing. 
     A memory controller  33  controls operations to input AV data from an MPEG encoder  35  and output AV data to an MPEG encoder  36  in order to implement simultaneous recording and playback operations. The memory controller  33  also is connected to an ATA (AT Attachment) I/F  38  by way of a data bus  37 , for controlling interface operations to input and output data from and to a buffer  34 . 
     The buffer  34  comprising two banks A and B is used for temporarily storing data input and output to and from the host computer  2 . For example, data read out from the bank A is supplied to the HDD  1 , while at the same time, data supplied by the MPEG encoder  35  is stored in the bank B. As these two simultaneous operations are completed, the HDD  1  is switched from the bank A to the bank B, consequently, the MPEG encoder  35  is switched from the bank B to the bank A. Thus, data read out from the bank B is now supplied to the HDD  1 , while at the same time, data supplied by the MPEG encoder  35  is now stored in bank A. 
     The MPEG encoder  35  receives an AV signal from an external host such as a television receiver not shown in the figure, encoding video and audio signals individually in accordance with the MPEG format, and then multiplexes the signals before supplying them to the memory controller  33 . In the MPEG decoder  36 , video data and audio data are separated from each other by a demultiplexer (not shown) before each is decoded. The MPU  31 , the host RAM  32 , the memory controller  33  and the ATA I/F  38  are connected to the data bus  37 . 
     The ATA I/F  38  serves as an interface between the HDD  1  and the host computer  2  through the data bus  37 . The functions of the HDD  1  are the same as what have been described earlier by referring to FIG.  10 . 
     Next, basic operations of the host computer  2  are explained. An AV signal received from an external host not shown in the figure such as a television receiver is supplied to the MPEG encoder  35 . The MPEG encoder  35  encodes video and audio signals individually in accordance with the MPEG system, and then multiplexes the signals by using an incorporated multiplexer (not shown) before supplying them to the memory controller  33 . The memory controller  33  outputs the AV data to the buffer  34  to be stored therein temporarily. The MPU  31  controls the memory controller  33  to read out the AV data back from the buffer  34  by fixed units and outputs the data to the HDD  1  to be recorded therein. 
     In a playback operation, on the other hand, the MPU  31  gives a command to the memory controller  33  to read out AV data of a predetermined amount from the HDD  1  and store the AV data into the buffer  34 . Receiving the command, the memory controller  33  reads out AV data of a predetermined amount from the HDD  1  and stores the AV data into the buffer  34  temporarily. The AV data read out by the memory controller  33  is supplied to the MPEG decoder  36 . The MPEG decoder  36  separates the AV data received from the buffer  34  into video data and audio data, decodes the video and audio data separately and outputs them as an AV signal. 
     FIG. 2 is a diagram showing a relation between the amount of transferred data in sectors and the lapse of time in an operation to transfer AV data of  2  channels encoded in accordance with the MPEG from the HDD  1  to the host computer  2 . The AV data is transferred at a transfer rate of eight Mbps. In the case where the number of pictures (N) is 15 and the appearance frequency of I- and P-pictures is 3, the size of GOP (Group of Pictures) data is 512 KB (1,024 sectors). Assuming that the cluster size is 256 KB (512 sectors), a GOP comprises two clusters. 
     Data of channel  1  is read out from its first cluster after completing a seek operation by the magnetic head, a time to wait for the disc to rotate to a desired position and a track jump, those to be done within the first 50-ms period of time. During the following 50-ms period of time, the data of channel  1  is transferred to the host computer  2 . During the third and fourth 50-ms periods of time, the data of channel  2  is read out from its first cluster and transferred to the host computer  2 , so that the operation to read out and transfer the data of channel  1  is temporarily suspended. Then, at the beginning of the fifth 50-ms period of time, the operation to read out and transfer the data of channel  1  is resumed from its second cluster and, at the end of the sixth 50-ms period of time, the operation to read out and transfer the data of channel  1  from its first and second clusters (=2×512 sectors) is ended. Likewise, during the fifth and sixth 50-ms periods of time, the operation to read out and transfer the data of channel  2  is suspended temporarily. Similarly, at the beginning of the seventh 50-ms period of time, the operation to read out and transfer the data of channel  2  is resumed from its second cluster and, at the end of the eighth 50-ms period of time, the operation to read out the data of channel  2  from its first and second clusters (=2×512 sectors) is ended. 
     In order to sustain the continuity of a data transfer, the following conditional relation must be satisfied: 
     
       
         (HDD internal transfer rate)×(Transfer allowable time) (Required amount of transferred data . . .   (1) 
       
     
     The total number of transfers (m) required to transfer one GOP is m=GOP/cluster size. In the case of the example shown in FIG. 2, m=1,024 sectors/512 sectors=2. That is to say, in order to transfer AV data of one GOP (=1,024 sectors) which is recorded in 2 clusters each having a size of 512 sectors, twice of transfers are required. 
     The above formula can be expressed in terms of actual parameters as follows: 
     
       
         (e×RDRV)×(TGOP/(n×m)−(TSEEK+TREV)) RMPEG×TGOP/m . . .   (2) 
       
     
     where: 
     n is the number of recording or playback channels, 
     e is a format efficiency, 
     TGOP is a GOP time (sec), 
     RMPEG is an MPEG transfer rate (Mbps), 
     TSEEK is a maximum seek time (sec), 
     TREV is a disc revolution time (sec) and 
     RDRV is an internal transfer rate in the HDD (Mbps). 
     In the above formula, a worst fragmentation state is taken into consideration. In a worst fragmentation state, a wait time comprising a head seek time and a disc revolution time is entailed each time an access is made to a cluster in which data is recorded. It should be noted that the above formula does not consider a time to carry out retry processing in the event of an error detected during an operation to read out data and defect processing after the retry processing. 
     The size of one GOP is expressed as follows: 
     GOP (Mbit)=RMPEG×TGOP 
     Since one GOP comprises m clusters, the size of a cluster is expressed as follows: 
     
       
         Cluster (Mbit)=GOP (Mbit)/m=RMPEG×TGOP/m . . .   ( 2   a ) 
       
     
     By rearranging formula (2), TGOP can be found as follows: 
     
       
         TGOP (TSEEK+TREV)×e×RDRV×n×m/(e×RDRV-n×RMPEG . . .   ( 2   b ) 
       
     
     It should be noted that formula ( 2   b ) is derived by normal algebraic manipulation of formula (2), details of which are omitted. By substituting the expression on the right-hand side of formula ( 2   b ) for TGOP in equation ( 2   a ), the size of a cluster is expressed as follows: 
     Cluster (Mbit) 
     
       
         RMPEG×(TSEEK+TREV)×e×RDRV×n/(e×RDRV-n×RMPEG)=(TSEEK+TREV)/(e×RDRV-n×RMPEG)/(e×RDRV×n×RMPEG) =(TSEEK+TREV)/{1/(n×RMPEG)−1/(e×RDRV)} 
       
     
     Thus, Cluster (Mbit) (TSEEK+TREV)/{1/(n×RMPEG)−1/(e×RDRV)} 
     Since one Mbit=1,024/8 kbyte=128 kbyte, Cluster (kbyte)=128×cluster (Mbit). Thus, 
     Cluster (kbyte) 
      128×(TSEEK+TREV)/{1/(n×RMPEG)−1/(e×RDRV)} . . .   (3) 
     As described above, a wait time comprising a head seek time and a disc revolution time is entailed each time an access is made to a cluster in which data is recorded. Now, in addition to the head seek time and the disc revolution time, consider a time to carry out retry processing in the event of an error detected in an operation to read out data. In this case, the size of a cluster is expressed as follows: 
     Cluster (kbyte) 
     
       
         128×(TSEEK+(1+NRTRY)×TREV)/{1/(n×RMPEG)−1/(e×RDRV)} . . .   (4) 
       
     
     where NRTRY is the number of retries. As shown in formula (4), the size of the cluster is found in the same way as formula (3) except that the retry processing has an effect of lengthening the disc revolution time TREV by (1+NRTRY) times. 
     The formula for finding the size of a cluster from the upper limit NRTRY of the number of retries with the retry processing taken into consideration can be simplified as follows: 
     Cluster (kbyte) 
     
       
         (3+NRTRY)/{3/(4×n×RMPEG)−1/RDRV} . . .   (5) 
       
     
     The above simplified formula is obtained for a 3.5-inch ATA HDD, a disc revolution speed of 5,400 RPM, a TSEEK value of 0.02 sec, a TREV value of 0.01 sec and a format efficiency e of 0.78 which is a realistic value. 
     Conversely, by rearranging formula (4), the number of allowable retries NRTRY can be found from a given cluster size as follows: 
     NRTRY 
      Cluster×{1/(n×RMPEG)−1/(e×RDRV)}/(128×TREV)TSEEK/TREV−1 . . .   (6) 
     At the beginning of a data transfer, the MPU  31  computes the number of allowable retries from the number of channels specified in a transfer request by using the above formula. 
     FIG. 3 is a diagram showing a typical structure of a data management format of a recording area in the HDD  1 . As shown in the figure, the entire recording area of the disc  18  in the HDD  1  is controlled by using consecutive LBAs, namely, from LBA 0  to LBAN. 
     LBA 0  to LBAM- 1  are used for recording AV data whereas the remaining LBAM to LBAN are used for recording an IT (Information Technology) data. The IT recording area comprises an audio-data area, a TOC (Table of Contents) area and a secondary-defect-list area. The AV-data recording area and the audio-data area constitute an area in which user data can be recorded. On the other hand, the TOC area and the secondary-defect-list area are referred to as a system-management area. 
     AV data is recorded in cluster units in dependence on a recording mode of the system. The recording bit rate varies from mode to mode. In an edit mode for recording editable data, the recording bit rate is typically eight Mbps. An SP mode for recording video data of a relatively high quality at a typical recording bit rate of 4 Mbps is inferior to the edit mode. An LP mode with a recording bit rate of typically 2 Mbps is used for recording video data over a long period of time, although the quality of which is not that high. A cluster is a collection of a plurality of logical blocks. A cluster is a smallest data recording unit on a disc. The size of a cluster varies in dependence on the recording mode and can be found by using computation formula (4) or (5) given above. 
     FIG. 4 is a diagram showing a layout of clusters of user data and system-management data to be recorded. As shown in the figure, the size of a cluster of user data which can be video or audio data varies in accordance with the recording mode and is found by using computation formula (4) or (5) given above. It should be noted that data is recorded into the system-management area in logical-block units. A file unit of AV data is referred to as a title. 
     FIG. 5 is a diagram showing relations between the number of channels and the cluster size of transferred data with the number of allowable retries taken as a parameter. To be more specific, the diagram shows relations for allowable-retry counts of zero and one for writing attempt. As shown it the figure, the size of a cluster for an allowable-retry count of 0 can be made smaller than that of an allowable-retry count of 1 as is also obvious from formula (4) or (5). In addition, the size of a cluster also increases for a larger number of channels as is obvious from formulas (3), (4) and (5). 
     FIG. 6 is a diagram showing relations between the number of transfer channels and the required size of the buffer  34  with the number of allowable retries taken as a parameter. To be more specific, the diagram shows relations for allowable-retry counts of zero and one for writing attempt. As shown in the figure, the size of the buffer  34  for an allowable-retry count of zero can be made smaller than that of an allowable-retry count of one. In addition, the required size of the buffer also increases for a larger number of channels. 
     The following description explains processing to play back data from the system-management area when the host computer  2  is activated with reference to a flowchart shown in FIG.  7 . As shown in the figure, the flowchart begins with a step Si at which the MPU  31  reads out information in the TOC area and information in the secondary-defect list area from the system-management area. The information recorded in the TOC area on the HDD  1  is referred to hereafter as dTOC information. The flow of the processing then goes on to a step S 2  at which the MPU  31  writes the information of the TOC area read out at the step S 1  at an predetermined address in the host RAM  32 , creating  0 TOC information.  0 TOC information is TOC information written into the host RAM  32 . Then, the flow of the processing goes on to a step S 3  at which the MPU  31  writes the information of the secondary-defect list area read out at the step S 1  at a predetermined address in the host RAM  32 , creating a new-defect table. When the processing of the step S 3  is completed, the host computer  2  enters a state to wait for a next instruction. 
     The following description explains operations carried out by the host computer  2  to record AV data with reference to a flowchart shown in FIG.  8 . As shown in the figure, the flowchart begins with a step S 11  at which the MPU  31  acquires the title and a recording mode of AV data to be recorded from a user interface unit shown in none of the figures. The flow of the processing then goes on to a step S 12  at which the MPU  31  acquires the number of recording channels represented by parameter n in formula (3) as well as a recording rate represented by parameter RMPEG in formula (3) from the title and the recording mode acquired at the step S 11 , and then computes the cluster size by using formula (3). The MPU  31  may also determine the cluster size using a lookup table containing values calculated from formula (3). It should be noted that the other parameters used in formula (3), namely, TSEEK, TREV, e and RDRV, are known values which are unique to the HDD  1 . 
     Then, the flow of the processing goes on to a step S 13  at which the MPU  31  selects TOC information on a free recording area on the disc from the  0 TOC information stored in the host RAM  32 . As described above, the  0 TOC information has been created from the dTOC information stored in the HDD 1  at the step S 2  of the flowchart shown in FIG.  7 . 
     Then, the flow of the processing goes on to a step S 14  at which the MPU  31  forms a judgment as to whether or not a new defect exists in a blank area selected at the step S 13 . The formation of the judgment is based on the new-defect table created at the step S 3  of the flowchart shown in FIG.  7  and stored in the host RAM  32 . If the outcome of the judgment indicates that a new defect exists, the flow of the processing goes on to a step S 15 . At the step S 15 , the MPU  31  identifies the address of a cluster that includes the new defect and excludes the cluster from the blank area. If the outcome of the judgment indicates that a new defect does not exist, on the other hand, the flow of the processing goes on to a step S 16  directly, skipping the step S 15 . At the step S 16 , the MPU  31  writes data for the blank area at a predetermined address in the embedded RAM  40  and creates iWTOC information. That is to say, TOC information in the embedded RAM  40  is used as iTOC information, iTOC information at recording is used as iWTOC information and iTOC information at playback is used as iRTOC information. 
     The flow of the processing then goes on to a step S 17  at which the MPU  31  acquires the number of recording channels represented by parameter n in formula (6) as well as a recording rate represented by parameter RMPEG in formula (6) from the title and the recording mode acquired at the step S 11 , and then acquires the cluster size in formula (6) which was computed at the step S 12 . Then, the MPU  31  computes NRTRY, the number of allowable retries, by using formula (6). The MPU  31  may also determine the NRTRY using a lookup table containing values calculated from formula (6). It should be noted that the other parameters used in formula (6), namely, TSEEK, TREV, e and RDRV, are known values which are unique to the HDD  1 . The MPU  31  informs the HDD  1  of the value of NRTRY so that the HDD  1  will not carry out retry operations a number of times exceeding the value of NRTRY. 
     In the HDD  1  to which the present invention is applied, an upper limit of the number of allowable retries is received from the host computer  2  as a command. Typically, in the ATA system, this command is defined newly as a special command. The host computer  2  issues a retry restricting command specifying an upper limit of the number of allowable retries to the HDD  1 . When the number of retries carried out in an operation to read out or write data from or into the disc has reached the upper limit in the event of an error, the HDD  1  transmits data including the error occurred in the sector to the host computer  2 . At the same time, the HDD  1  sets error status to interrupt the host computer  2 . From this interruption, the host computer is informed of a defect address. 
     The flow of the processing then goes on to a step S 18  at which the MPU  31  finds the number of times (N) a record command is to be issued. The value of N varies in dependence on the recording mode of a title to be recorded. The recording mode determines how many bytes can be recorded with one record command. For example, in the case of the edit mode set as a recording mode, the value of N is 3 since the size of the data is more than two times the amount of data that can be recorded in each record command. The flow of the processing then goes on to a step S 19  at which the MPU  31  sets the count value of N found at the step S 18  in a record-command-issuance counter. 
     The flow of the processing then goes on to a step S 20  at which the MPU  31  converts an HBA (Host Block Address) into an LBA. An HBA is an address for controlling the AV-data recording area in the host computer  2 . The flow of the processing then goes on to a step S 21  at which the MPU  31  issues a record command to the HDD  1  through the data bus  37  and the ATA I/F  38 . The record command requests the HDD  1  to record the title which was acquired at the step S 11  from the user interface unit. The record command is issued on the basis of the iWTOC information stored in the embedded RAM  40 . To be more specific, a cluster into which data can be recorded is selected as a recording location from the TOC information on a blank area which is part of the iWTOC information. 
     The flow of the processing then goes on to a step S 22  at which the MPU  31  forms a judgment as to whether or not the count value of the record-command-issuance counter is equal to 0. If the outcome of the judgment formed at the step S 22  indicates that the count value of the record-command-issuance counter is not equal to 0, the flow of the processing goes on to a step S 23  at which the MPU  31  decrements the value of the record-command-issuance counter set at the step S 19  by 1. Then, the flow of the processing goes back to the step S 21  at which the MPU  31  issues another record command to the HDD  1 . 
     If the outcome of the judgment formed at the step S 22  indicates that the count value of the record-command-issuance counter has become equal to 0 or the recording command has been issued (N+1) times, on the other hand, the flow of the processing goes on to a step S 24 . At the step S 24 , the MPU  31  forms a judgment as to whether or not the operation to record the title acquired at the step S 11  to be completed. If the MPU  31  judges that the operation to record the title is not to be completed, the flow of the processing goes back to the step S 19  at which the value of N is set in the record-command-issuance counter for recording data into the next cluster. Then, the pieces of processing of the steps S 20  to S 24  are repeated. As the outcome of the judgment formed at the step S 24  indicates that the operation to record the title is completed, the host computer  2  is put in a wait state. 
     Next, operations carried out by the host computer  2  to play back AV data are explained by referring to a flowchart shown in FIG.  9 . As shown in the figure, the flowchart begins with a step S 31  at which the MPU  31  acquires the title of AV data to be played back from the user interface unit which is shown in none of the figures. The flow of the processing then goes on to a step S 32  at which the MPU  31  selects information on a TOC area according to the title from the 0TOC information stored in the host RAM  32 . As described earlier, the 0TOC information was created from the dTOC information recorded in the HDD  1  at the step S 2  of the flowchart shown in FIG.  7 . The flow of the processing then goes on to a step S 33  at which the MPU  31  writes the 0TOC information selected at the step S 32  at a predetermined address in the embedded RAM  40  in the MPU  31  to create iRTOC information. 
     The flow of the processing then goes on to a step S 34  at which the MPU  31  acquires the number of playback channels represented by parameter n in formula (6), a playback rate represented by parameter RMPEG in formula (6) and the size of a cluster in which the data is recorded (that is, the parameter Cluster in formula (6)) from the recording mode of the title to be played back. Then, the MPU  31  computes NRTRY, the number of allowable retries, by using formula (6) and issues the retry restriction command to HDD  1 . It should be noted that the other parameters used in formula (6), namely, TSEEK, TREV, e and RDRV, are known values which are unique to the HDD  1 . Then, the flow of the processing goes on to a step S 35  at which the MPU  31  finds the number of times (N) a playback command is to be issued in dependence on the recording mode (or the size of the cluster) of the title to be played back. The flow of the processing then goes on to a step S 36  at which the MPU  31  sets the count value of N found at the step S 35  in a playback-command-issuance counter. 
     The flow of the processing then goes on to a step S 37  at which the MPU  31  converts an HBA (Host Block Address) for controlling the AV-data recording area in the host computer  2  into an LBA. The flow of the processing then goes on to a step S 38  at which the MPU  31  issues a playback command to the HDD  1  through the data bus  37  and the ATA I/F  38 . The playback command requests the HDD  1  to play back the title which was acquired at the step S 31  from the user interface unit. 
     The flow of the processing then goes on to a step S 39  at which the MPU  31  forms a judgment as to whether or not an error exists in the playback AV data supplied by the HDD  1  through the ATA I/F  38 . If the outcome of the judgment indicates that an error exists in the playback AV data, the flow or the processing proceeds to a step S 40  at which the MPU  31  sets the cluster containing the playback AV data with an error detected at the step S 39  as a new-defective recording area by cataloging the HBA of the defective cluster in the new-defect table stored in the embedded RAM  40 . 
     The flow of the processing then goes on to a step S 41 . If the outcome of the judgment formed at the step S 39  indicates that an error does not exist in the playback AV data, on the other hand, the flow of the processing proceeds to the step S 41  directly, skipping the step S 40 . At the step S 41 , the MPU  31  forms a judgment as to whether or not the count value of the playback-command-issuance counter set at the step S 36  is equal to 0. If the outcome of the judgment formed at the step S 41  indicates that the count value of the playback-command-issuance counter is not equal to 0, the flow of the processing goes on to a step S 42  at which the MPU  31  decrements the count value of the record-command-issuance counter by 1. Then, the flow of the processing then goes back to the step S 38  at which the MPU  31  issues another playback command to the HDD  1 . 
     If the outcome of the judgment formed at the step S 41  indicates that the count value of the playback-command-issuance counter has reached equal to 0, that is, if the number of times the playback command is issued has reached (N+1), on the other hand, the flow of the processing goes on to a step S 43 . At the step S 43 , the MPU  31  forms a judgment as to whether or not the operation to play back the title acquired at the step S 31  is to be completed. If the MPU  31  judges that the operation to play back the title is not to be completed, the flow of the processing goes back to the step S 36  at which the value of N is set in the playback-command-issuance counter for recording data into the next cluster. Then, the pieces of processing of the steps S 37  to S 43  are repeated. As the outcome of the judgment formed at the step S 43  indicates that the operation to record the title is completed, the host computer  2  is put in a wait state. 
     It should be noted that the restriction on the retry operations imposed at the step S 17  of the flowchart shown in FIG. 8 or the step S 34  of the flowchart shown in FIG. 9 can also be based on time instead of the number of retries. 
     In addition, data can be recorded into and read out from the IT recording area including the system-management area in LBA units by making accesses to the HDD  1  with no restriction on the number of retries. The defect processing is the ordinary defect processing implemented in the HDD  1 . The processing can be accessed at an error rate assured by an ordinary HDD. 
     It should be noted that, presentation media for presenting a computer program to be executed for carrying the processing described above can be information recording media such as a magnetic disc and a CD-ROM or transmission media using a network such as the Internet and a digital satellite. 
     As described above, according to a recording/playback apparatus, a recording/playback method and a presentation medium of the present invention, a defect in a data recording area of a recording medium causing an operation to record or play back data into or from the area to end in a failure is determined by counting the number of times an operation to record or play back data into or from the area ends in a failure, and an upper limit of the number of times used as a criterion for determining a defect is adjusted in accordance with the size of a unit of the operation to record or play back data into or from the recording medium. As a result, data can be recorded and played back without losing the continuity of the data. 
     In addition, according to a recording/playback apparatus, a recording/playback method and a presentation medium of the present invention, a defect in a data recording area of a recording medium causing an operation to record or play back data into or from the area to end in a failure is determined by counting the number of times an operation to record or play back data into or from the area ends in a failure, and an upper limit of the number of times used as a criterion for determining a defect is adjusted in accordance with a transfer rate and the number of transfer channels in the operation to record or play back data into or from the recording medium. As a result, data can be recorded and played back without losing the continuity of the data. 
     Having now fully described the invention, it will be apparent to one of ordinary skill in the art that many changes and modifications can be made thereto without departing from the spirit and scope of the invention as set forth herein.