Defect management method for a magnetic recording medium

In a method of carrying out defect management on reading data from a disk-shaped magnetic recording medium comprising a plurality of tracks separated into a user data area available to a user, an alternate area, and a management area, the method comprises the steps of retrying reading operation of data up to a maximum retry count when an error is detected on reading of data for a target sector in the user data area and of registering the target sector in a defect table in the management area and writing read-out data in an alternate sector in the alternate area in a case where a retry count is not less than a specific count when retry results in a success. Alternatively, the method comprises the steps of retrying reading operation of data up to a maximum retry count when an error is detected on reading of data for a target sector in the user data area, of overwriting read-out data in the target sector in a case where a retry count is not less than a specific count when retry results in a success, and of registering the target sector in a defect table in the management area and writing read-out data in an alternate sector in the alternate area in a case where an error is detected when overwritten data is reread from the target sector.

BACKGROUND OF THE INVENTION
 This invention relates to a defect management method on occurrence of an
 error when data are read out of a magnetic recording medium such as a
 flexible or floppy disk (which may be abbreviated to "FD") or a hard disk
 (which may be abbreviated to "HD") that is accessed by a magnetic
 recording and reproducing device such as a flexible or floppy disk drive
 (which may be abbreviated to "FDD") or a hard disk drive (which may be
 abbreviated to "HDD").
 Although description will be made a case where the magnetic recording and
 reproducing device is the flexible disk drive and the magnetic recording
 medium is the flexible disk, of course, application is not restricted to
 this case.
 As is well known in the art, the flexible disk drive of the type described
 is a device for carrying out data recording and reproducing operation to
 and from a magnetic disk medium of the flexible disk loaded therein. In
 recent years, the flexible disks are more and more improved to have a
 larger storage capacity. Specifically, development is made of the flexible
 disks having the storage capacity of 128 Mbytes (which may be called
 large-capacity FDs) in contrast with the flexible disks having storage
 capacity of 1 Mbytes or 2 Mbytes (which may be called small-capacity FDs).
 Following such development, the flexible disk drives have also improved to
 accept the large-capacity FDs for data recording and reproducing
 operations to and from the magnetic recording media of the large-capacity
 FDs. Furthermore, the large-capacity FDs are more improved to have a
 larger storage capacity of 256 Mbytes, 512 Mbytes, . . . , and so on.
 Throughout the present specification, flexible disk drives capable of
 recording and reproducing data for magnetic recording media of the
 large-capacity FDs alone will be referred to as high-density exclusive
 type FDDs. On the other hand, flexible disk drives capable of recording
 and reproducing data for magnetic recording media of the small-capacity
 FDs alone will be called low-density exclusive type FDDs. Furthermore,
 flexible disk drives capable of recording and reproducing data for
 magnetic recording media of both the large-capacity and the small-capacity
 FDs will be called high-density and low-density compatible type FDDs. In
 addition, the high-density exclusive type FDDs and the high-density and
 low-density compatible type FDDs will collectively be called high-density
 type FDDs.
 The low-density exclusive type FDD and the high-density type FDD are
 different in mechanism from each other in several respects, one of which
 will presently be described. In either FDD, a pair of magnetic heads is
 supported by a carriage which is driven by a drive arrangement to move in
 a predetermined radial direction with respect to the magnetic disk medium
 of the flexible disk loaded in the flexible disk drive. The difference
 resides in the structure of the structure of the drive arrangement. More
 specifically, the low-density exclusive type FDD uses a stepping motor as
 the drive arrangement. On the other hand, the high-density type FDD uses a
 linear motor such as a voice coil motor (which may be abbreviated to
 "VCM") as the drive arrangement.
 Now, description will be made in slightly detail as regards the voice coil
 motor used as the drive arrangement in the high-density type FDD. The
 voice coil motor comprises a voice coil and a magnetic circuit. The voice
 coil is disposed on the carriage at a rear side and is wound around a
 drive axis extending in parallel to the predetermined radial direction.
 The magnetic circuit generates a magnetic field in a direction
 intersecting that of an electric current flowing through the voice coil.
 With this structure, by causing the electric current to flow through the
 voice coil in a direction intersecting that the magnetic field generated
 by the magnetic circuit, a drive force occurs in a direction extending to
 the axis on the basis of interaction of the electric current with the
 magnetic field. The drive force causes the voice coil motor to move the
 carriage in the predetermined radial direction.
 Another difference between the low-density exclusive type FDD and the
 high-density type FDD resides in the number of revolution of a spindle
 motor for rotating the magnetic disk medium of the flexible disk loaded
 therein. More specifically, the low-density exclusive type FDD may rotate
 the magnetic disk medium of the small-capacity FD loaded therein at a low
 rotation speed having the number of revolution of either 300 rpm or 360
 rpm. On the other hand, the high-density type FDD can admit, as the
 flexible disk to be loaded thereinto, either the large-capacity FD alone
 or both of the large-capacity FD and the small-capacity FD. As a result,
 when the large-capacity FD is loaded in the high-density type FDD, the
 spindle motor for the high-density type FDD must rotate the magnetic disk
 medium of the large-capacity FD loaded therein at a high rotation speed
 having the number of revolution of 3,600 rpm which is equal to ten or
 twelve times as large as that of the small-capacity FD.
 In the meanwhile, the large-capacity FD generally has an external
 configuration identical with that of the small-capacity FD. Specifically,
 both of the large-capacity and the small-capacity FDs have a flat
 rectangular shape of a width of 90 mm, a length of 94 mm, and a thickness
 of 3.3 mm in case of a 3.5-inch type. However, the large-capacity FD has a
 narrower track width (track pitch) than that of the small-capacity FD. As
 a result, it is difficult for the large-capacity FD to position a magnetic
 head of the high-density type FDD on a desired track in the magnetic
 recording medium thereof in contrast with the small-capacity FD.
 Accordingly, a servo signal for position detection is preliminarily
 written in the magnetic disk medium of the large-capacity FD.
 In the meanwhile, the flexible disk about to manufactured (which will be
 called a raw flexible disk) comprises merely a magnetic disk medium having
 both surface coated by the magnetic material. In order to enable to make
 the raw flexible disk utilize for an electronic device such as a personal
 computer or a word processor, it is necessary for the row flexible disk to
 partition the magnetic disk medium into a plurality of regions with
 respective addresses and to record and manage what information should be
 written in each region. Such a sequence of processing steps is called a
 format(ting) or an initialization.
 In general, the flexible disk comprises the magnetic disk medium on which a
 plurality of tracks are arranged with concentric circles around a center
 of rotation thereof. Each track is divided in a circumferential direction
 into a predetermined number of sectors having a length equal to one
 another.
 The formatting is classified into a physical formatting and a logical
 formatting. The physical formatting determines how data is arranged on the
 magnetic disk medium. Specifically, the physical formatting determines the
 total tracks, the total usable tracks, the number of sectors in each
 track, a medium storage capacity, a format storage capacity, and so on. On
 the other hand, the logical formatting determines locations where
 information corresponding to table of contents is written on the magnetic
 disk medium and assigns address to units each of which writes information.
 The logical formatting is also called a sector formatting.
 In addition, the sector formatting is performed by using a servo writer and
 a media formatter. The servo writer partitions first each sector into a
 servo field and a data field to write the above-mentioned serve signal in
 the servo field. In this event, the sectors on each track are assigned
 with sector numbers in the circumferential direction in order. Thereafter,
 the media formatter carries out test of the sector format and preparation
 of a defect map. The defective map is called a defect table.
 Specifically, not that all of the tracks on the magnetic disk medium can be
 used by a user, an area available to the user is restricted. Such an area
 is referred to as a user data area. Tracks other than the user date area
 are used as alternate tracks for replacing defective sectors in the user
 data area or the like. Such an area for the alternate tracks is called an
 alternate area. In addition, another area for storing the above-mentioned
 defect map and other management tables is referred to as a management
 area. The alternate area is generally disposed in the magnetic disk medium
 in the radial direction inward while the management area is disposed in
 the magnetic disk medium in the radial direction outward. In addition,
 separation of the tracks into the user data area, the alternate area, and
 the management area is carried out in the physical formatting.
 The media formatter first performs test of the sector format to detect the
 detective sectors on the user data area. Subsequently, the media formatter
 carries out rearrangement of the sectors except for the defective sectors.
 Thereafter, the media formatter prepares the above-mentioned defect map or
 defect table. The defect map or the defect table is a table for entering
 information indicating where the defective sectors on the user data area
 are arranged to which alternate sectors in the alternate area. The defect
 map or the defect table is stored in a predetermined sector in the
 management area. If a sector-formatted flexible disk has the storage
 capacity which is less than a predetermined specification storage capacity
 due to the presence of a lot of defective sectors, the sector-formatted
 flexible disk is discarded because the sector-formatted flexible disk
 cannot be used any longer.
 As described above, there are various types of the large-capacity FDs so as
 to have the storage capacity of 128 Mbytes or 256 Mbytes. Throughout the
 present specification, the large-capacity FD having the storage capacity
 of 128 Mbytes is called a single-density large-capacity FD while the
 large-capacity GD having the storage capacity of 256 Mbyte is called a
 double-density large-capacity FD. Although each of the single-density
 large-capacity FD and the double-density large-capacity FD has the same
 line recording density, the same sector format (serve format), and the
 same number of disk revolution, the single-density large-capacity FD and
 the double-density large-capacity FD have different track densities from
 each other. That is, the double-density large-capacity FD has the track
 density twice as large as that of the single-density large-capacity FD.
 Although the above-mentioned description is made as regards processing on
 the formatting, such sector management or defect management may be carried
 out on usual read-out/write-in operation of data after the formatting
 comes to end.
 In the manner which will later be described in conjunction with FIG. 1, in
 a conventional read command processing, when reading operation of data is
 imperfect, retry is repeated up to a maximum retry count. When data is
 normally read after several retries without amounting to the maximum retry
 count, the read command processing comes to a correct end without
 performing any processing.
 However, it is feared that data normally read after several retries becomes
 to be broken down in the near future so that a sector (which is called a
 data sector) storing the data becomes a defective sector. Nevertheless, in
 the conventional read command processing comes to the correct end without
 performing any processing. In other words, no processing is carried out
 when retry results in a success.
 Another read command processing is disclosed in Japanese Unexamined Patent
 Publication of Tokkai No. Hei 6-251,503 or JP-A 6-251,503 which has a
 title of "METHOD FOR CONTROLLING FLEXIBLE DISK DEVICE." According to JP-A
 6-251,503, management information is stored in an information management
 area. In addition, when retry results in a failure, data stored in a
 target sector is copied in the information management area. However, in
 JP-A 6-251,503 also, no processing is carried out when retry results in a
 success in the similar manner as the above-mentioned conventional read
 command processing.
 SUMMARY OF THE INVENTION
 It is therefore an object of the present invention to provide a defect
 management method which is capable of carrying out protection of data
 stored in the data sector before the data sector progressively becomes a
 defective sector due to a defect or the like.
 It is another object of the present invention to provide a defect
 management method of the type described, which is capable of reducing a
 retry count on reading operation of data.
 It is still another object of the present invention to provide a defect
 management method of the type described, which is capable of shortening a
 date readout time.
 Other objects of this invention will become clear as the description
 proceeds.
 On describing the gist of this invention, it is possible to be understood
 that a method carries out defect management on reading data from a
 disk-shaped magnetic recording medium to be accessed. The magnetic
 recording medium comprises a plurality of tracks thereon which are
 arranged with concentric circles. Each track is divided in a
 circumferential direction into a predetermined number of sectors having a
 length equal to one another. The plurality of tracks are separated into a
 user data area available to a user, an alternate area, and a management
 area.
 According to an aspect of this invention, the above-mentioned method
 comprises the steps of retrying reading operation of data up to a maximum
 retry count when an error is detected on reading of data for a target
 sector in the user data area and of registering the target sector in a
 defect table in the management area and writing read-out data in an
 alternate sector in the alternate area in a case where a retry count is
 not less than a specific count when retry results in a success.
 According to another aspect of this invention, the above-mentioned method
 comprises the steps of retrying reading operation of data up to a maximum
 retry count when an error is detected on reading of data for a target
 sector in the user data area, of overwriting read-out data in the target
 sector in a case where a retry count is not less than a specific count
 when retry results in a success, and of registering the target sector in a
 defect table in the management area and writing read-out data in an
 alternate sector in the alternate area in a case where an error is
 detected when overwritten data is reread from the target sector.
 On describing the gist of this invention, it is possible to be understood
 that a recording medium records a program to make a computer execute
 defect management on reading data from a disk-shaped magnetic recording
 medium to be accessed. The magnetic recording medium comprises a plurality
 of tracks thereon which are arranged with concentric circles. Each track
 is divided in a circumferential direction into a predetermined number of
 sectors having a length equal to one another. The plurality of tracks are
 separated into a user data area available to a user, an alternate area,
 and a management area.
 According to an aspect of this invention, the above-mentioned recording
 medium records the program to make the computer execute processing of
 retrying reading operation of data up to a maximum retry count when an
 error is detected on reading of data for a target sector in the user data
 area, and processing of registering the target sector in a defect table in
 the management area and of writing read-out data in an alternate sector in
 the alternate area in a case where a retry count is not less than a
 specific count when retry results in a success.
 According to another aspect of this invention, the above-mentioned
 recording medium records the program to make the computer execute
 processing of retrying reading operation of data up to a maximum retry
 count when an error is detected on reading of data for a target sector in
 the user data area, processing of overwriting read-out data in the target
 sector in a case where a retry count is not less than a specific count
 when retry results in a success, and processing of registering the target
 sector in a defect table in the management area and of writing read-out
 data in an alternate sector in the alternate area in a case where an error
 is detected when overwritten data is reread from the target sector.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
 Referring to FIG. 1, a conventional read command processing on occurrence
 of a read command will be described at first in order to facilitate an
 understanding of the present invention. The flexible disk drive comprises
 a controller or processor (not shown) for processing the read command.
 First, the controller seeks or locates a target cylinder using a magnetic
 head of the flexible disk drive (step S1). The step S1 is followed by a
 step S2 at which the controller initializes a retry count Nr to zero,
 namely, Nr=0. The step S2 proceeds to a step S3 at which the controller
 determines whether or not a target sector is detected on the target
 cylinder using the magnetic head. When the target sector is detected, the
 step S3 is succeeded by a step S4 at which the controller reads data out
 of the target sector using the magnetic head. The step S4 is followed by a
 step S5 at which the controller determines whether or not an error is
 detected in the read-out data. When no error is detected in the read-out
 data, the read command processing normally comes to a correct end.
 On the other hand, when any error is detected read-out data, the step S5
 proceeds to a step S6 at which the controller determines whether or not
 the retry count Nr exceeds a maximum retry count Nr(max) or
 (Nr&gt;Nr(max)). The maximum retry count Nr(max) is, for example, equal to
 fifty. When the retry count Nr is not more than the maximum retry count Nr
 (max), namely, Nr.gtoreq.Nr (max), the steps S6 is succeeded by a step S7
 at which the controller increments the retry count Nr by one. The step S7
 returns to the step S2 to repeat processing in the steps S3 through S6.
 When the retry count is more than the maximum retry count Nr(max), namely,
 Nr&gt;Nr(max), the read command processing comes to an error end.
 As described above, in the conventional read command processing, when
 reading of data is imperfect, retry is repeated up to the maximum retry
 count Nr(max). When data is normally read after several retries without
 amounting to the maximum retry count Nr(max), the read command processing
 comes to the correct end without performing any processing.
 However, it is feared that data normally read after several retries becomes
 to be broken down in the near future so that the data sector storing the
 data becomes a defective sector. Nevertheless, the conventional read
 command processing comes to the correct end without performing any
 processing, as mentioned in the preamble of the instant specification.
 Referring to FIG. 2, description will proceed to a high-density type
 flexible disk drive (FDD) to which a defect management method according to
 this invention is applicable. The illustrated high-density type FDD is a
 high-density and low-density compatible type FDD which enable to carry out
 recording and reproducing of data for magnetic recording media of both a
 large-capacity and a small-capacity flexible disks (FDs) which will later
 be described. The flexible disk is loaded into the high-density type FDD
 from an insertion direction indicated by an arrow A in FIG. 2. FIG. 2
 shows a state where the flexible disk is loaded into the high-density type
 FDD. The flexible disk has a disk center axis (not shown).
 The high-density type FDD comprises a main frame 11 having a main surface
 11a and a disk holder table 12 which is rotatably supported on the main
 surface 11a of the main frame 11. The disk holder table 12 has a table
 center axis O which acts as the axis of the rotation. The loaded flexible
 disk is held on the disk holder table 12 so that the table center axis O
 coincides with the disk center axis. The disk holder table 12 is rotatably
 driven by a spindle motor (SPM) 60. The spindle motor 60 is mounted on the
 main frame 11 with the spindle motor 60 put into a state embedded in a
 concave portion (not shown) of the main frame 11, thereby the magnetic
 disk medium of the flexible disk rotates at a desired rotation speed in
 the manner which will become clear. In addition, the main frame 11 has a
 back surface (not shown) on which a printed-circuit board 22 is mounted. A
 number of electronic parts (not shown) are mounted on the printed-circuit
 board 22.
 The high-density type FDD comprises a pair of magnetic heads (not shown)
 for reading/writing data from/to the magnetic disk medium 41 in the
 large-capacity FD 40. The magnetic heads are supported via gimbals 14 with
 a carriage 15. A combination of the gimbals 14 and the carriage 15 is
 called the carriage assembly. The carriage 15 is disposed over the main
 surface 11a of the main frame 11 with a space left therebetween. The
 carriage 15 supports the magnetic heads movably along a predetermined
 radial direction (i.e. a direction indicated by an arrow B in FIG. 2) with
 respect to the large-capacity FD 40.
 The carriage 15 is supported and guided at both lower sides thereof by a
 pair of guide bars 16 which extend to directions in parallel with the
 predetermined radial direction B. The carriage assembly in driven in the
 predetermined radial direction B by a voice coil motor (VCM) which will
 presently be described. As shown in FIG. 2, the carriage assembly is
 provided with a pair of voice coils 17 at opposite rear sides thereof. The
 voice coils 17 act as components of the voice coil motor.
 Now, description will be made as regards the voice coil motor (VCM). The
 voice coil motor comprises the pair of voice coils 17 located at the
 opposite rear sides of the carriage assembly and wounded around drive axes
 parallel to the predetermined radial direction B, and a pair of magnetic
 circuits 20 for producing magnetic fields intersecting electric currents
 flowing through the voice coils 17. In the voice coil motor of the
 above-mentioned structure, when the electric current is made to flow
 through each of the voice coils 17 in a direction intersecting the
 magnetic field produced by the magnetic circuits 20, a drive force is
 generated in an extending direction of each drive axis as a result of
 interaction between the electric current and the magnetic field. The drive
 force causes the voice coil motor to make the carriage assembly move in
 the predetermined radial direction B.
 As shown in FIG. 2, the spindle motor 60 is mounted on the main surface 11a
 with the spindle motor embedded in the concave portion of the main frame
 11. The spindle motor 60 comprises a spindle shaft 61 which is rotatably
 supported with respect to the main frame 11 via a ball bearing (not shown)
 substantially perpendicular to the main surface 11a of the main frame 11.
 The spindle shaft 61 serves as the axis O of the rotation for the magnetic
 disk medium of the flexible disk loaded in the high-density type FDD. The
 disk holder table 12 is fixed to the spindle shaft 61 at an upper portion
 thereof. The disk holder table 12 has a main surface which extends to a
 direction perpendicular to a longitudinal direction (a direction of the
 axis O of the rotation) of the spindle shaft 61.
 That is, the disk holder table 12 is rotatably supported on the main
 surface 11a of the main frame 11 and holds the flexible disk loaded in the
 high-density type FDD so that the table center axis O (the axis of the
 rotation) coincides with the disk center axis of the flexible disk.
 Turning to FIGS. 3A and 3B, description will proceed to the large-capacity
 FD depicted at 40. FIG. 3A is a plane view of the large-capacity FD 40 as
 seen from an upper surface side while FIG. 3B is a bottom view of the
 large-capacity FD 40 as seen from a lower surface side. The illustrated
 large-capacity FD 40 is a 3.5-inch type and comprises a magnetic disk
 medium 41, a jacket 42 for receiving or covering the magnetic disk medium
 41. The jacket 42 consists of an upper shell 42-1 (FIG. 3A) having the
 upper surface and a lower shell 42-2 (FIG. 3B) having the lower surface.
 As shown in FIG. 3B, in the lower shell 42-2, a jacket or shell circular
 opening 42a is formed at a center portion of the large-capacity FD 40. In
 the jacket circular aperture 42a is freely received a supporting hub 43
 for supporting the magnetic recording medium 41. The supporting hub 43 has
 a hub center hole 43a at a center portion thereof and a chucking hole (a
 disk driving oval hole) 43b at a position eccentric with the center
 position thereof. The hub center hole 43a has substantially a rectangular
 shape and receives the spindle shaft 61 (FIG. 2) therein in the manner
 which later be described. The chucking hole 43b freely receives a chucking
 pin or a drive roller 62 (FIG. 2) therein in the manner which will also
 later be described.
 Turning back to FIG. 2 again in addition to FIG. 3A, the disk holder table
 12 has a table diameter which is greater than that of the supporting hub
 43 and which is smaller than that of the jacket circular opening 42a of
 the jacket 42.
 The disk holder table 12 has a table driving oval hole 12a at a position
 corresponding to the chucking hole (the disk driving oval hole) 43b.
 Through the table driving oval hole 12a, the chucking pin (the drive
 roller) 62 is freely received in the chucking hole 43b of the flexible
 disk 40 in the manner which will later become clear. The disk holder table
 12 is mounted on a magnetic case 63 at a bottom surface thereof. The
 chucking pin 62 is rotatably and movably mounted in the magnetic case 63
 with the chucking pin 62 urged upwardly. Accordingly, the chucking pin 62
 moves downwardly or sinks in the disk holder table 12 if any load is
 applied to the chucking pin 62 downwards. The magnetic case 63 comprises a
 circumferential wall (not shown) having an outer surface at a
 predetermined position of which an index detection magnet 64 of
 rectangular parallelepiped shape is fixed.
 Referring to FIGS. 3A and 3B again, a write protection hole 44 is bored in
 the jacket 42 of the large-capacity FD 40 at a corner portion in rear and
 right-hand side with respect to the insertion direction A of FIG. 3B as
 view from the lower shell 42-2. In other words, the write protection hole
 44 is bored in the jacket 42 of the large-capacity FD 40 at the corner
 portion in rear and left-hand side in the insertion direction A of FIG. 3A
 as viewed from the upper shell 42-1. FIG. 3B shows a state where the write
 protection hole 44 is shut by a write protection tab 44a. The write
 protection tab 44a manually enables to slide along a direction in parallel
 with the insertion direction A. It is possible to carry out opening and
 closing of the write protection hole 44 by operating the write protection
 tab 44a manually. When the write protection hole 44 is closed by the write
 protection tab 44a, the large-capacity FD 40 is put into a write enable
 state. When the write protection hole 44 is opened by the write protection
 tab 44a, the large-capacity FD 40 is put into a write disable state.
 The illustrated large-capacity FD 40 shows a case where there is two types
 of storage capacity of, for example, 128 Mbytes and 256 Mbytes. In the
 vicinity of the write protection hole 44, a large-capacity identifier hole
 45 is bored in the jacket 42 of the large-capacity FD 40. The
 large-capacity identifier hole 45 is for identifying the large-capacity FD
 40 in distinction from the small-capacity FD. In addition, a type
 identifier hole 46 is selectively bored in the jacket 42 of the
 large-capacity FD 40 near the write protection hole 44 together with the
 large-capacity identifier 45. The type identifier hole 46 is for
 identifying a type of the large-capacity FD 40. It is possible to identify
 the type of the large-capacity ED 40 according to the presence or absence
 of the type identifier hole 46. It is assumed that the large-capacity FD
 40 having the storage capacity of 128 Mbytes is referred to as a first
 type of the large-capacity FD while the large-capacity FD 40 having the
 storage capacity of 256 Mbytes is referred to as a second type of the
 large-capacity FD. In the example being illustrated, the type identifier
 hole 46 is not bored in the jacket 42 of the first type of the
 large-capacity FD while the type identifier hole 46 is bored in the jacket
 42 of the second type of the large-capacity FD.
 Although illustration is omitted, as is well known in the art, the
 large-capacity identifier hole 45 and the type identifier hole 46 are not
 bored in the jacket of the small-capacity FD.
 Turning back to FIG. 2 in addition to FIGS. 3A and 3B, on the
 printed-circuit board 22 mounted on the back surface of the main frame 11,
 the high-density type FDD further comprises a switch unit 50 at a corner
 position in rear and left-hand side with respect to the insertion
 direction A. The switch unit 50 comprises a plurality of push switches
 which will presently be described. The switch unit 50 is for detecting the
 presence or absence of the write protection hole 44, the large-capacity
 identifier hole 45, and the type identifier hole 46.
 More specifically, the switch unit 50 comprises, as the push switches, a
 write control switch 51, a large-capacity detecting switch 52, and a type
 detecting switch 53. The write control switch 51 is a push switch for
 detecting the opening or closing state of the write protection hole 44.
 The write control switch 51 is disposed at a position corresponding to the
 write protection hole 44 when the large-capacity FD 44 is loaded in the
 high-density type FDD. The large-capacity detecting switch 52 is a push
 switch for detecting whether the loaded flexible disk is the
 large-capacity FD 40 or the small-capacity FD. The large-capacity
 detecting switch 52 is disposed at a position corresponding to the
 large-capacity identifier hole 45 when the large-capacity FD 40 is loaded
 in the high-density type FDD. The type detecting switch 53 is a push
 switch for detecting the presence or absence of the type identifier hole
 45. The type detecting switch 53 is disposed at a position corresponding
 to the type identifier hole 46 when the large-capacity FD is loaded in the
 high-density type FDD.
 Although illustration is omitted, a stator (not shown) of the spindle motor
 60 comprises a frequency generation pattern (which is abbreviated an FG
 pattern hereinafter) for detecting the rotation speed thereof. The FG
 pattern generates an FG signal having pulses which in number to sixty
 during one rotation of the spindle motor 60. As is well known in the art,
 300 rpm is equivalent to 5 Hz/rev while 3,600 rpm is equivalent to 60
 Hz/rev. As a result, the FG pattern generates the FG signal having a
 frequency of 300 Hz if the magnetic recording medium 11 of the
 small-capacity FD 10 rotates at its prescribed rotation speed of 300 rpm
 by the spindle motor 60. Likewise, the FG pattern generates the FG signal
 having a frequency of 3,600 Hz if the magnetic recording medium 41 of the
 large-capacity FD 40 rotates at its prescribed rotation speed of 3,600 rpm
 by the spindle motor 60.
 As shown in FIGS. 3A and 3B, the large-capacity FD 40 further comprises a
 shutter 47 at a front side thereof. The shutter 47 is slidable in a
 direction depicted at C in FIGS. 3A and 3B. The shutter 47 is provided
 with a shutter window 47a. The shutter 47 is urged by a shutter spring in
 a direction reverse to the direction C. When the shutter 47 makes sliding
 movement in to the direction C, the shutter window 47a of the shutter 47
 is faced to a head window 42b formed in the jacket 42. At this time, it is
 possible to access the magnetic disk medium 41 by upper and lower magnetic
 heads (not shown) through the head window 42b.
 Turning back to FIG. 2, the high-density type FDD includes a shutter drive
 mechanism for opening and closing the shutter 47 of the large-capacity FD
 40, an ejector mechanism for ejecting the large-capacity FD 40, and a
 carriage locking mechanism for locking a direct-acting type carriage
 mechanism (which will later be described) after rejection of the
 large-capacity FD 40.
 The high-density type FDD further comprises a lever unit 70. The lever unit
 70 comprises an eject lever 71 and a lock lever 72. The eject lever 71
 serves both as a component of the shutter drive mechanism for opening and
 closing the shutter 47 and as a component of the ejector mechanism for
 ejecting the large-capacity FD 40 from the high-density type FDD. The lock
 lever 72 is located in the vicinity of the direct-acting type carriage
 mechanism and serves to lock the direct-acting type carriage mechanism
 upon ejection of the large-capacity FD 40.
 The ejector mechanism comprises an eject bottom 54 projecting into an outer
 surface of a front bezel (not shown) of the high-density type FDD, an
 eject plate 55 for positioning the large-capacity FD 40 loaded through an
 insertion slot (not shown) of the front bezel so that one surface of the
 large-capacity FD 40 is faced to the eject plate 55, and a pair of eject
 springs (not shown) having one end engaged with the eject plate 55 and the
 other end engaged with a disk holder unit (not shown). The eject plate 55
 has a rack 55a at its top end in a depth direction. The rack 55a is
 engaged with a pinion (not shown) rotatably supported on the main surface
 11a of the main frame 11. The lever unit 70 is urged by a spring mechanism
 73 in a counterclockwise direction.
 It is assumed that the large-capacity FD 40 is loaded into the disk holder
 unit of the high-density type FDD. Specifically, when the large-capacity
 FD 40 is inserted in the direction depicted at the arrow A in FIG. 2, a
 top end 71a of the eject lever 71 is engaged with an upper end 47b of a
 right side edge of the shutter 47. With the movement of the large-capacity
 FD 40 in the insertion direction A, the lever unit 70 is rotated in a
 clockwise direction. Consequently, the shutter 47 is forced by the top end
 71a of the eject lever 71 to make sliding movement in the direction C.
 When the large-capacity FD 40 is completely received in the disk holder
 unit of the high-density type FDD, the disk holder unit comes down and
 then the large-capacity FD 40 is locked by a disk lock mechanism (not
 shown) to be stably held in the disk holder unit. In this state,
 engagement between side arms (not shown) of the carriage assembly and the
 disk holder unit is released and the shutter window 47a of the shutter 47
 is located directly above the head window 42b of the jacket 42, as
 illustrated in FIG. 3A. Accordingly, the upper and the lower magnetic
 heads are in contact with the magnetic disk medium 41 of the
 large-capacity FD 40 through the shutter window 47a of the shutter 47 and
 the head window 42b of the jacket 42. The shutter 47 is urged by the
 shutter spring to be located at a position indicated by a dash-and-dot
 line in FIG. 3A.
 Turning back to FIGS. 3A and 3B, the jacket 42 has a first notch 42c formed
 on a forward side thereof in the insertion direction A. The jacket 42
 further has a second notch 42e formed on a lateral side provided with a
 chamfered portion 42d for preventing reverse insertion (wrong insertion in
 a vertical direction or in the insertion direction A). The second notch
 42e has a particular shape and is formed at a particular position so that
 the second notch 42e in reverse insertion preventing lever (not shown) of
 the small-density exclusive type FDD. In other words, the jacket of the
 small-capacity FD does not have the first and the second notches 42c and
 42e.
 Referring to FIG. 4, the description will proceed to the disk-shaped
 magnetic disk medium or the disk-shaped magnetic recording medium 41 to
 which the defect management method according to this invention is
 applicable. The magnetic recording medium 41 comprises a plurality of
 tracks 411 thereon which are arranged with concentric circles around a
 center of rotation thereof. Each track 411 is divided in a circumferential
 direction into a predetermined number of sectors 412 having a length equal
 to one another.
 It will be assumed that the large-capacity FD 40 is a single-density
 large-capacity FD which has the storage capacity of 128 Mbytes. In this
 event, the single-density large-capacity FD 40 or the magnetic recording
 medium 41 comprises the tracks 411 which are equal in total number and in
 available total number to 1,866 and 1,564 each side, respectively. Each
 track 411 is divided into the sectors 412 which are equal in number to 80.
 The single-density large-capacity FD has a medium storage capacity of
 about 160 Mbytes in all both sides and has a format storage capacity of
 about 128 Mbytes in all both side. That is, a physical format for the
 single-density large-capacity FD 40 or the magnetic recording medium 41
 arranges the tracks 411 on the magnetic recording medium 41 with
 concentric circles that are equal in number to 1,564 on one side and
 divides each track 411 into the sectors 412 which are equal in number to
 80.
 It will be presumed that the large-capacity FD 40 is a double-density
 large-capacity FD which has the storage capacity of 256 Mbytes. Inasmuch
 as the double-density large-capacity FD has the track density twice as
 large as that of the single-density large-capacity FD as described above,
 a physical format for the double-density large-capacity FD 40 or the
 magnetic recording medium 41 arranges the tracks 411 on the magnetic
 recording medium 41 with concentric circles that are equal in number to
 3,128 on one side and divides each track 411 into the sectors 412 which
 are equal in number to 80. In addition, each sector 412 consists of a
 servo field (not shown) and a data field (not shown).
 The magnetic recording medium 41 of the large-capacity FD 40 has a medium
 rotation speed of 3,600 rpm. In this connection, a magnetic recording
 medium of the small-capacity FD has a medium rotation speed of 300 or 360
 rpm. That is, the medium rotation speed of the large-capacity FD 40 is
 twelve or ten times as large as that of the small-capacity FD.
 As shown in FIG. 4, the tracks 411 on the magnetic recording medium 41 are
 separated into a user data area 413 available to a user, an alternate area
 414 and a management area 415 other than the user data area 413. In the
 illustrated magnetic recording medium 41, the alternate area 414 is
 disposed in the magnetic recording medium 41 in a radial direction inward
 while the management are 415 is disposed in the management area 415 is
 disposed in the magnetic recording medium 41 in the radial direction
 outward.
 The management area 415 of the magnetic recording medium 41 is provided
 with a predetermined sector 415a for storing a defect map or a defect
 table (which will later become clear) and with specific sectors for
 storing a defect management program which will later be described.
 Referring to FIG. 5 in addition to FIG. 4, description will proceed to a
 sector formatting method for the magnetic recording medium 41.
 The sector formatting is performed by using a servo writer (not shown) and
 a media formatter (not shown). The servo writer partitions first each
 sector 412 into the servo field and the data field to write a serve signal
 in the servo field (step S21). Thereafter, the media formatter carries out
 test of the sector format and preparation of the defect map (the defect
 table).
 Specifically, the media formatter first performs test of the sector format
 to detect the detective sectors on the user data area 413 (step S22). In
 the example being illustrated, it is assumed that there is defective
 sectors depicted at x1, x2, . . . , and so on as shown in FIG. 4.
 Subsequently, the media formatter carries out rearrangement of the sectors
 except for the defective sectors (step S23). In the example being
 illustrated, the media formatter carries out rearrangement of the sectors
 412 so that the defective sectors x1 and x2 are alternated by alternate
 sectors depicted as O1 and O2 in the alternate area 414, respectively.
 Thereafter, the media formatter prepares the above-mentioned defect map
 (defect table) to store the defect map (defect table) in the predetermined
 sector 415a of the management area 415 (step S24). The defect map (defect
 table) is a table for entering information indicating where the defective
 sectors x1, x2, . . . on the user data area 413 are arranged to which
 alternate sectors O1, O2, . . . in the alternate area 414. If such a
 sector-formatted flexible disk 40 has the storage capacity which is less
 than a predetermined specification storage capacity due to the presence of
 a lot of defective sectors, the sector-formatted flexible disk 40 is
 discarded because the sector-formatted flexible disk 40 cannot be used any
 longer.
 The large-capacity FD 40 having such a formatted magnetic recording medium
 41 is put on the market to be bought by a user. In addition, the user
 loads the large-capacity FD 40 in the high-density type FDD such as a
 high-density and low-density compatible type FDD illustrated in FIG. 2 to
 enable the high-density type FDD to carry out recording and reproducing
 (writing and reading) of data on the magnetic recording medium 41 of the
 large-capacity FD 40.
 Now, the present invention relates to a defect management method on
 carrying out a read command processing on such a formatted magnetic
 recording medium 41.
 Referring to FIG. 6, the description will proceed to a defect management
 method according to a first embodiment of this invention. The illustrated
 defect management method is similar in structure and operation to the read
 command processing illustrated in FIG. 1 except that the defect management
 method further comprises steps S8 and S9. The flexible disk drive
 comprises a controller or processor (not shown) for realizing the defect
 management method.
 First, the controller seeks or locates a target cylinder using a magnetic
 head of the flexible disk drive (step S1). The step S1 is followed by a
 step S2 at which the controller initializes a retry count Nr to zero,
 namely, Nr=0. The step S2 proceeds to a step S3 at which the controller
 determines whether or not a target sector is detected on the target
 cylinder using the magnetic head. When the target sector is detected, the
 step S3 is succeeded by a step S4 at which the controller reads data out
 of the target sector using the magnetic head. The step S4 is followed by a
 step S5 at which the controller determines whether or not an error is
 detected in the read-out data.
 On the other hand, when any error is detected read-out data, the step S5
 proceeds to a step S6 at which the controller determines whether or not
 the retry count Nr exceeds a maximum retry count Nr(max) or
 (Nr&gt;Nr(max)). The maximum retry count Nr(max) is, for example, equal to
 fifty. When the retry count Nr is not more than the maximum retry count
 Nr(max), namely, Nr.gtoreq.Nr(max), the steps S6 is succeeded by a step S7
 at which the controller increments the retry count Nr by one. The step S7
 returns to the step S2 to repeat processing in the steps S3 through S6.
 When the retry count is more than the maximum retry count Nr(max), namely,
 Nr&gt;Nr(max), the read command processing comes to an error end.
 The above-mentioned processing is similar to that illustrated in FIG. 1.
 Although the conventional read command processing immediately comes to a
 correct end when no error is detected in the read-out data at the step S5,
 the defect management method according to the first embodiment of this
 invention carries out processing in the steps S8 and S9.
 Specifically, at the step S8, the controller determines whether or not the
 retry count Nr is not less than a specific count Nr(spc). The specific
 count Nr(spc) is, for example, equal to five. However, the specific count
 Nr(spc) is not restricted to five and may be any count selected between
 one, inclusive, and the maximum retry count Nr(max), exclusive, namely,
 1.gtoreq.Nr(spc)&lt;Nr(max). In addition, in a case where the maximum
 retry count Nr(max) is equal to fifty, desirably the specific count
 Nr(spc) may be a range between three and eight, both inclusive.
 When the retry count Nr is less than the specific count Nr(spc), namely,
 Nr&lt;Nr(spc), the controller ends the read command processing because the
 controller determines that it is not feared that the target sector becomes
 the defective sector. On the contrary, if the retry count Nr is not less
 than the specific count Nr(spc), the controller determines that it is
 feared that the target sector becomes the defective sector in the near
 future and the step S8 proceeds to the step S9. At the step S9, the
 controller registers or stores the target sector in the defect table (the
 predetermined sector 415a in FIG. 4) and writes the read-out data in an
 alternate sector in the alternate area 414.
 By carrying out the above-mentioned defect management, it is possible to
 previously protect data stored in the data sector before the data sector
 in the user data area 413 becomes the defective sector progressively due
 to defect or the like. Accordingly, inasmuch as it is possible to decrease
 the retry count Nr on reading of data, it is possible to shorten a data
 readout time.
 Referring to FIG. 7, the description will proceed to a defect management
 method according to a second embodiment of this invention. The illustrated
 defect management method is similar in structure and operation to that
 illustrated in FIG. 6 except that steps S11 through S13 are inserted
 between the steps S8 and S9. Accordingly, the description will be made
 about only points different from FIG. 6 in order to avoid repetition of
 the description.
 Although the step S8 directly proceeds to the step S9 in the first
 embodiment illustrated in FIG. 6 when the retry count Nr is not less than
 the specific count Nr(spc), namely, Nr.gtoreq.Nr(spc), the step S8
 proceeds to the step S11 in the second embodiment.
 At the step S11, the controller overwrites or rewrites the read-out data in
 the target sector using the magnetic head. The step S11 is succeeded by
 the step S12 at which the controller rereads the overwritten data from the
 target sector using the magnetic head. The step S12 is followed by the
 step S13 at which the controller determines whether or not an error is
 detected in the read-out data. When no error is detected in the read-out
 data, the controller ends the read command processing. On the other hand,
 when any error is detected in the read-out data, the step S13 proceeds to
 the step S9.
 It is clear that the second embodiment has similar merits in the first
 embodiment. In the second embodiment, data is written in the alternate
 sector only when collect data is read out of the target sector although
 the data is overwritten in the target sector. As a result, it is possible
 to carry out protection of data stored in the target sector only when it
 is feared that the target sector certainly becomes the defective sector in
 the near future.
 While this invention has thus far been described in conjunction with
 preferred embodiments thereof, it will now be readily possible for those
 skilled in the art to put this invention into various other manners. For
 example, it is clear that this invention may be applicable to other
 magnetic recording media such as a hard disk (HD) as well as the large
 capacity FD.
 In addition, although the above-mentioned embodiments are made about a case
 of carrying out normal reading and writing of data, the defect management
 method may be carried out on the sector formatting illustrated in FIG. 5.
 That is, the defect management illustrated in FIG. 6 or FIG. 7 may be
 carried out after the step S24 in FIG. 5. Inasmuch as the large-capacity
 FD 40 having such a formatted magnetic recording medium 41 has an
 extremely small retry count on reading operation of data, it is possible
 to shorten a data readout time.
 Furthermore, a program realizing the defect management method illustrated
 in FIG. 6 or FIG. 7 may be recorded in a recording medium (not shown) such
 as the magnetic recording medium 41 illustrated in 4. Herein, the
 "recording medium" means a recording medium for recording the program
 which enables a computer to read. For example, the recording medium may be
 a compact disc read-only memory (CD-ROM), a magnetic disk such as a floppy
 or flexible disk, a semiconductor memory, or the like. In addition, the
 recording medium may be that distributed via a communication medium. At
 any rate, it is possible for the computer to carry out the predetermined
 processing by installing the program from the recording medium in the
 computer.