Preformatting an optical disk with positioning information in boundary areas between non-written information block areas

Reading partly written record carriers using a reading device which positions the read head on the basis of written marks presents problems when an information block behind a non-written area must be read. A writing device and a method of writing information blocks on a record carrier of a rewritable type such as a CD-RW or a DVD-RAM include the following. First, record carrier areas which are in use for writing information blocks, are detected, for example, using the corresponding writing instructions. Subsequently, it is detected whether boundary areas adjoining the areas which are in use are unwritten. In that case, the boundary areas are initialized by writing them with dummy information, preferably with dummy information blocks comprising address information in the conventional manner. A record carrier is provided with status information which is indicative of the non-written state of areas. A reading device is provided with search means for searching written areas. Apparatus is provided for programming a computer system to provide programmed apparatus to implement the method.

BACKGROUND OF THE INVENTION
 The invention relates to a device for writing information blocks in a track
 pattern on a record carrier of a rewritable type, which device is provided
 with a writing unit for writing areas of the record carrier via (i.e. by
 using) a beam of electromagnetic radiation with marks representing the
 information blocks, and positioning means for positioning the writing unit
 based on a track structure which defines a track pattern on the record
 carrier.
 The invention also relates to a method of writing information blocks in a
 track pattern on a record carrier of the rewritable type. Marks
 representing the information blocks are written in areas of the record
 carrier via a writing unit via a beam of electromagnetic radiation. The
 writing unit is positioned on the basis of a track structure which defines
 the track pattern.
 The invention further relates to a record carrier for use in the writing
 device.
 Moreover, the invention relates to a reading device for reading information
 blocks represented by optically readable marks in a track pattern on a
 record carrier. The device is provided with a reading unit for reading the
 marks via a beam of electromagnetic radiation, and apparatus for
 positioning the reading unit on the basis of the marks.
 A writing device, a method and a record carrier of the type described in
 the opening paragraph for writing information blocks are known from U.S.
 Pat. No. 4,901,300 (PHN 12.398). In the system described in that document,
 information blocks are recorded in a track pattern on the record carrier
 and represented by optically readable marks. The record carrier has a
 track structure in the form of a wobbling pregroove having a varying
 frequency which represents position information. The writing device has a
 write head for scanning the record carrier via a beam of electromagnetic
 radiation. The tracking signals are derived from reflected radiation. The
 writing device includes for positioning the write head during scanning
 based on the position information. During scanning, the wobble causes a
 modulation in the tracking signals. This modulation comprises the position
 information coded therein, which indicates the absolute position in the
 track with respect to the starting point of the area intended for
 information. The information blocks are recorded on the record carrier at
 a desired position in conformity with their address, while the write head
 is positioned, if necessary via a jump to another radial position in the
 track, on the basis of the position information. A record carrier may have
 been partly written and then includes written areas in which marks are
 present, and non-written areas in which only the track structure is
 present. There are reading devices which derive the tracking signals
 and/or position information from the marks.
 SUMMARY OF THE INVENTION
 The inventors recognize the position information can not be generated in
 non-written areas, so that a partly written record carrier is not reliably
 readable.
 It is, inter alia, an object of the invention to provide apparatus with
 which a partly written record carrier can be read more reliably.
 In accordance with a first aspect of the invention, a writing device is
 therefore characterized in that the device is provided with first
 detection means for detecting areas of the record carrier which are in use
 for writing information blocks, and second detection apparatus for
 detecting non-written boundary areas adjoining the areas which are in use,
 and initialization apparatus for writing the non-written boundary areas
 with dummy information. The writing device according to the invention has,
 inter alia, the advantage that partly written record carriers can be read
 reliably by reading devices which derive tracking signals and position
 information from marks, because boundary areas adjoining isolated
 information blocks have been written. When a radial jump to such an area
 is made, the reading unit will be globally positioned a short distance
 ahead of the information block to be read, for example, on the basis of
 distance information derived from a speed sensor on a motor for displacing
 the reading unit. The reading unit will then reach the adjoining area a
 short distance ahead of the information block to be read. In this area,
 the marks of the dummy information are present and the reading unit can
 therefore be accurately positioned in a conventional manner on the basis
 of information read from the record carrier. A further advantage is that
 boundary areas are written beyond the information block to be read, for
 the case where, due to inaccuracies during global positioning, the reading
 unit is positioned a short distance behind the information block to be
 read.
 It is to be noted that a disc storage system is known from EP 0 328 240, in
 which the area on a disc-shaped record carrier intended for data storage
 is successively formatted in parts whenever a part is necessary for actual
 data storage. During formatting, areas are provided with position
 information before they are put into use and analyzed by way of writing
 and subsequent reading, with error control information being generated on
 the basis of the analysis. In the system according to the invention, the
 position information is already present in the track structure and areas
 which are not in use, namely the non-written boundary areas of areas which
 are in use, are written with dummy data by way of a writing action before
 or after an area for data storage has been put into use.
 An embodiment of the device according to the invention is characterized in
 that the first detection apparatus are adapted i.e. have structures to
 enable it to detect the areas which are in use depending upon writing
 instructions received by the device. This has the advantage that whether
 areas are in use, can be determined without using storage means.
 A further embodiment of the device according to the invention is
 characterized in that the first detection means are adapted to detect the
 areas which are in use depending upon use information on the record
 carrier. This has the advantage that whether areas are in use, can be
 directly determined from the use information without having to read the
 relevant areas themselves for this purpose.
 A further embodiment of the device according to the invention is
 characterized in that the initialization apparatus are adapted to write a
 band-shaped area having a predetermined width. In this case, the
 non-written boundary areas are at least sufficient through a minimal width
 for forming a landing area for landing a reading unit of a reading device
 after a jump has been made. The width is chosen to be such that, in a
 majority of the standard reading devices, the reading unit will land
 within this width in the case of a jump. This has the advantage that the
 partly written record carrier can be read reliably by means of standard
 reading devices.
 A further embodiment of the device according to the invention is
 characterized in that the initialization apparatus are adapted to write at
 an instant subsequent to performing a writing instruction, the instant
 being determined in dependence upon operational circumstances. This has
 the advantage that a user is hindered as little as possible by the
 initialization performance.
 A further embodiment of the device according to the invention is
 characterized in that the dummy information is organized as N dummy
 information blocks, in which N is at least one and the information blocks
 are provided with position information. In these adjoining areas, the
 initialization apparatus write dummy information blocks which includes
 position information in the conventional manner, such as, for example
 addresses. This has the advantage that the reading unit can determine the
 position of the reading unit in the conventional manner based on the
 position information. At a small value of N, the written boundary area may
 be too small to land the reading unit, but a run-in area will have been
 formed for locking in reading apparatus prior to reading an information
 block in the relevant area which is in use. This is an advantage in a
 reading device according to the invention, which reading device can search
 the written area because the reading unit approaches the information block
 via the run-in area and the tracking means and read signal decoding means
 can lock in.
 In accordance with a second aspect of the invention, a record carrier for
 use in the writing device is characterized in that the record carrier is
 provided with status information about the non-written or written state of
 areas on the record carrier, which status information can be reproduced in
 a predetermined manner. This has the advantage that, after reproducing the
 status information via the detection apparatus for detecting the written
 areas, the writing device knows the status of an area which is either
 written or not written and can therefore quickly decide whether
 initialization is necessary, because the area does not need to be read
 first. This requires a shorter time for performing a writing instruction
 and for initializing, if necessary, adjoining areas.
 In accordance with a third aspect of the invention, a reading device is
 characterized in that the reading device is provided with search apparatus
 for searching an area written with marks. The reading device can follow
 the track only via marks and generate position information. When areas
 which are not contiguous and are separated by non-written areas are read,
 the reading unit will generally land a short distance ahead of the
 information block to be read, when a jump to such an area is made. The
 search means now have the advantage that a written area is searched, for
 example by displacing the reading unit further towards the jump until
 marks are found. Consequently, the reading device according to the
 invention can reliably read a partly written record carrier.
 Those skilled in the art will understand the invention and additional
 objects and advantages of the invention by studying the description of
 preferred embodiments below with reference to the following drawings which
 illustrate the features of the appended claims:

DESCRIPTION OF THE PREFERRED EMBODIMENTS
 FIG. 1a shows a disc-shaped record carrier 1 provided with a track 9
 intended for recording and a central hole 10. The track 9 is arranged in
 accordance with a spiral pattern of windings 3. The track 9 is indicated
 on the record carrier by a track structure which is provided during
 manufacture of the blank record carrier. The track structure is
 constituted, for example by a pregroove 4 which enables the read/write
 head to follow the track 9 during scanning. FIG. 1b is a cross-section
 taken on the line b--b of the record carrier 1, in which a transparent
 substrate 5 is provided with a recording layer 6 and a protective layer 7.
 The pregroove 4 may be implemented as a pit or elevation, or it may have a
 material property deviating from its ambience. Moreover, the track
 structure may consist of an alternation of raised and deepened windings,
 referred to as land and groove patterns, with a transition from land to
 groove or vice versa taking place per winding. The recording layer 6 may
 be optically or magneto-optically writeable by means of a device for
 reading and/or writing information such as the known CD-Recordable. The
 information is organized in blocks and is represented by optically
 readable marks 11 in the form of a succession of areas reflecting much and
 little radiation, such as a succession of pits of different lengths in a
 CD. Such a rewritable disc is provided in the system of the new
 high-density optical disc, the Digital Versatile Disc (DVD). FIGS. 1c and
 1d show two examples of a periodical modulation (wobble) of the pregroove.
 This wobble causes an extra signal in a tracking servosensor. The wobble
 is, for example, frequency-modulated and the position information such as
 an address or a time code is coded in the modulation. A description of a
 writeable CD system, which is provided with position information in this
 way, can be found in U.S. Pat. No. 4,901,300 and U.S. Pat. No. 5,187,699
 hereby incorporated in whole by reference. A track structure may also
 include, for example, regularly divided partial patterns which
 periodically cause tracking signals. Another example of a track structure
 are header symbols formed by optically readable marks which are indicative
 of an address and indicate the start of the area for recording an
 information block. This description is based on information storage in a
 spiral track pattern which is filled from the inside to the outside, for
 example as in CD-ROM. The invention is applicable in a corresponding
 manner with other track patterns, in which the windings are concentric
 instead of spiral, or with differently formed record carriers such as
 optical tapes.
 FIG. 2 shows diagrammatically a partly written disc-shaped record carrier
 1. A lead-in area, file management information and use information is
 recorded in a first written area 21. Furthermore, a second and a third
 written area 22 and 23 are shown, which are isolated and are in use for
 storing use information. It is true that the record carrier 1 is provided
 with a track structure as described with reference to FIG. 1, but for a
 standard reading device it is not satisfactorily usable for positioning
 when the standard reading device derives the tracking and/or position
 information on the basis of marks. The entirely written area 21 will be
 readable for any reading device, because marks are present uninterruptedly
 from a radius to be minimally used (for the relevant type of record
 carrier). However, when such a standard reading device must read the
 isolated areas 22 or 23, for example addressed via a read command, it will
 displace a read head via a jump to a radial position in conformity with
 the address. After a global positioning, the standard reading device will
 attempt to read position information on the record carrier for a
 precision-positioning. However, since no marks are found, a standard
 device will not be able to further position the reading unit and will not
 reproduce information. If the track structure includes headers which are
 constituted by marks, the standard reading device will in principle be
 able to read them. However, due to the absence of intermediate marks in
 non-written areas, it will not be possible to position the reading unit
 satisfactorily above the track and reading of the headers in a non-written
 area is unreliable.
 FIG. 3 shows a partly written record carrier with dummy information
 according to the invention. In addition to the areas 21, 22, 23 which are
 in use in FIG. 2, areas 31, 32 and 33 are initialized by writing them with
 marks. The initialized area 31 adjoins the isolated area 22 in a reading
 direction viewed in the radial direction from the central hole 10. In the
 case of an instruction for reading the area 22, a reading device will
 position a read head a short distance in front of this area. A first
 global positioning is based on the actual position (for example, in the
 file management information in area 21) and the displacement, for example,
 measured via a displacement sensor on the radial drive motor of the
 reading unit. The reading unit will then land in the initialized area 31.
 Subsequently, an accurate positioning takes place on the basis of
 reflected radiation via the marks of the dummy information. The reading
 unit can now be positioned accurately above the track and finds the
 desired area 22 by just following the track. In an embodiment of the
 invention, the dummy information is organized as dummy information blocks,
 for example with a fixed content such as zeros (Zero Blocks, ZB). The ZBs
 are provided in the conventional manner with control and address
 information, for example in headers. The organization of the ZB preferably
 does not deviate from ordinary information blocks, for example as regards
 error correction and the headers. When a reading unit finds such a ZB, the
 current position of the reading unit is derived therefrom in the
 conventional manner after global positioning and, based on this current
 position, the precision-positioning then takes place, for example by
 jumping several tracks from track to track.
 In an embodiment of the system according to the invention, dummy
 information is also written in a boundary area 32 situated behind the
 isolated area 22 which is in use. During global positioning, the reading
 unit may also land in this boundary area 32 just beyond the desired area
 22. The accurate positioning, in this case by jumping a number of tracks
 back to a position ahead of the area 22 which is in use, can now be based
 on the current position derived from the dummy information in the boundary
 area 32 situated behind it. The width (in the radial direction) of this
 boundary area 32 may be chosen to be smaller than the width of the area
 31, because the global positioning is directed at a position ahead of the
 area 22 which is in use. The width of the subsequent area 32 may be chosen
 to be, for example approximately equal to the difference of the width of
 the preceding area 31 minus the width of the area 22 which is in use. For
 this purpose, the width of the area 22 which is in use should be known.
 The boundary areas 31 and 32 and the combination of the boundary areas 31,
 32 and the area which is in use constitute a tape-shaped area within which
 a reading unit may land during global positioning. The width of this
 tape-shaped area is chosen depending on the expected positioning
 tolerances in the envisaged reading devices. In practice, for example a
 global positioning within 0.2 mm is possible. The width is then at least
 0.2 mm, which yields a tape-shaped area of approximately 270 windings at a
 track pitch of 0.74 .mu.m. In, for example a DVD-ROM, the entire record
 carrier may be written at a standard speed within approximately 1 hour and
 has a total writeable area of approximately 34 mm radially, so that the
 initialization of 0.2 mm will require approximately 20 seconds. If the
 record carrier must be made suitable for a reading device according to the
 invention, it is sufficient to initialize a narrower area. At a high
 transport speed of the reading unit during a jump, this reading device
 will at least recognize a difference between a written and a non-written
 area. After it has reached a written area, this reading device will
 decrease the transport speed so that the marks in the written area can be
 read and position information can be derived therefrom. It is to be noted
 that, in principle, eccentricity of the track pattern, in so far as is
 allowed within the system specifications of the record carrier, does not
 need to be added to the positioning tolerance because the written area
 will then be situated under a reading unit anyway during a part of a
 revolution and the positioning means can then lock in. Also a tolerance in
 the radial direction of the start of the area intended for data storage,
 for example the radial position of the information block with address
 0000, does not need to be taken into account, because the distance between
 the jumps will be determined relatively with respect to a current head
 position.
 In a further embodiment of the system according to the invention, the dummy
 information is written in a boundary area 33 preceding the area 23 which
 is in use. This area includes a small number of dummy information blocks
 (at least one) in the track directly preceding the area which is in use. A
 reading device according to the invention, as described hereinafter with
 reference to FIG. 5, is provided with apparatus for searching written
 areas after global positioning. It is then an advantage that the area 23
 which is in use and is to be read is preceded by a written area 33 so that
 the tracking apparatus and read apparatus of such a reading device can
 lock in before the area to be read starts. The same applies to a standard
 reading device which, for example, in the case of a track structure with
 headers, can position the reading unit sufficiently accurately and reaches
 the area to be read. When the area is reached, the tracking and read
 apparatus are then in a locked-in state and the desired information blocks
 will then be read in a reliable manner.
 FIG. 4 shows a device for writing information blocks on a disc-shaped
 record carrier which is writeable, for example in a magneto-optical or
 optical way (via phase change) by means of a beam of electromagnetic
 radiation. During writing, marks representing the information are formed
 on the record carrier. The device is provided with drive apparatus 45 for
 rotating the record carrier 1, and with a write head 42 for scanning the
 track which is indicated by the track structure on the record carrier. The
 write head 42 is radially positioned with respect to the track by
 positioning apparatus 44, while position information is detected from the
 track structure. In accordance with known tracking and focus methods, the
 track is scanned with the write head and, for example, the tracking signal
 has a modulation due to the wobble in the pregroove. The tracking signal
 is demodulated and the position information coded therein is regained in
 the positioning apparatus 44 and passed on to the system control unit 46.
 The radial position of the write head can be verified via the regained
 position information. The information presented to the input of the write
 apparatus 41 is divided therein, if necessary, into information blocks and
 converted into a write signal for the write head 42. The writing apparatus
 41 include, for example, an error coder and a channel coder. The system
 control unit 46 controls the positioning apparatus 44, the writing
 apparatus 41, and the drive means 45 and are equipped to perform the
 procedures, described hereinafter, for detecting whether areas are in use,
 for detecting non-written boundary areas and initializing with dummy
 information.
 First, the system control unit 46 is adapted to detect whether information
 blocks are in use. In a first embodiment of this detection, the fact that
 the blocks are in use is derived from the received writing instructions
 and possibly also from successfully performed reading instructions. The
 moment the record carrier is introduced into the device, the system
 control unit keeps track of the areas which are in use, for example by
 using a list of addresses for a bit map in which each bit of a given
 address on the record carrier indicates the use information. For example,
 in a DVD the size of an information block is 32 kbyte so that a bit map
 for 8 Gbyte fits in one information block at 1 bit per information block.
 In the case of a writing instruction for a given address, the bit
 corresponding to this address is then set in the state indicating the
 in-use state. In a second embodiment, such a list or bit map on the record
 carrier is fixed (i.e. written) at a predetermined position, for example
 in or preceding the lead-in area where no use information may be stored.
 Instead, the use information may be stored as a file, while the rules of
 the file management system used (via Directories and Path Tables such as
 for example in ISO 9660) must be taken into account. In another
 embodiment, the use information is derived from information present on the
 record carrier in accordance with the file-management system, which
 information customarily comprises tables about the occupied or unoccupied
 state of addressable areas on the record carrier. Moreover, the system
 control unit may be adapted to search for written areas on the record
 carrier and subsequently decide on the basis of the contents of detected
 information blocks whether such an area is in use or is only initialized.
 Secondly, the system control unit 46 is adapted to detect whether areas
 adjoining areas in use, have been written. Non-written boundary areas are
 subsequently initialized, as described below. In a first embodiment, the
 writing unit is positioned, on the basis of the track structure, above
 areas which precede or succeed an area which is in use. The presence of
 marks can be customarily ascertained from the reflected radiation. If
 there are marks, the area has been written and may even be in use itself.
 A reading function, generally via a combined write/read unit, is present
 in the conventional writing device. By reading the relevant boundary
 areas, it can be directly ascertained whether the areas have been written.
 If the dummy information is distinguishable from standard information, it
 can also be determined from the contents read whether dummy information is
 concerned. This distinction may be provided, for example, in the header of
 the dummy information blocks or, for example, by intentionally providing
 an error pattern in the dummy information blocks. In a second embodiment,
 a record carrier according to the invention is provided with status
 information indicating whether areas on the record carrier are written or
 not written. In an embodiment of the writing device according to the
 invention, the system control unit is then adapted to write and read the
 status information on the record carrier. Depending on the mode chosen for
 fixing the status information, the system control unit knows the location
 of the status information or a reference to the status information or uses
 the file management information in a conventional manner so as to
 reproduce the status information. The status information may be fixed, for
 example in the form of a bit map, with one bit indicating the status of a
 fixed area having a size corresponding to the minimum length of an
 information block. In existing optical disc systems, this length is
 determined by the error-correcting coding mode used. As an alternative, or
 as a supplement, a table with written areas can be fixed in which at least
 the end of the first written area (viewed in the radial direction from the
 central hole) is given. Likewise as with the use information, the status
 information on the record carrier may also be fixed at a predetermined
 position on the record carrier, for example, in or preceding the lead-in
 area where no use information may be stored. Another suitable position is
 near the end of the area intended for data storage, because, viewed
 globally, the record carrier will be filled from the beginning. If the
 area near the end is required for data storage when the record carrier is
 almost completely filled, the status information will be limited to a
 small quantity or may be dispensed with completely because then
 (substantially) no non-written areas will be left. Instead, the status
 information may be fixed as a file. In one embodiment of the writing
 device, the validity of this status information is determined after
 reading status information of the record carrier. A very safe method is to
 read areas to be initialized always first and then perform the
 initialization only if these areas are actually still unwritten.
 Consequently, the time required for initialization is doubled, but there
 is still an advantage with respect to the previously mentioned system in
 which status information is not used because in this system all areas must
 be read first, whereas now, in accordance with the status information, a
 part of the areas does not need to be read. In another embodiment, for
 example, extra validity information may be stored on the record carrier.
 For performing a first writing instruction, the device writes the validity
 information on the record carrier, indicating that the record carrier may
 include more written areas or areas in use than is indicated by the status
 and/or use information present thereon. Operational circumstances
 permitting, a new version of the status and/or use information is fixed,
 whereafter lastly the validity information is fixed again, now with the
 contents that the status and/or use information is completely up to date.
 If the session is interrupted, for example due to current drop-out or
 manual removal of the record carrier, the validity information on the
 record carrier indicates that the status information is incomplete. The
 temporary status information which has not been fixed yet is preferably
 stored in the writing device in a non-volatile memory so that after
 termination of a current drop-out the temporary status information can as
 yet be fixed. In another embodiment, a further indication may be included
 in the validity information, namely that a number of areas are still to be
 initialized before the record carrier completely complies with the
 requirements of a reading device, for example "partly ROM drive prepared"
 and a list of boundary areas which are still to be initialized. Moreover,
 for example, a gradation of the minimum width of the described areas may
 be included, for example, "minimal ROM drive landing area 0.2 mm".
 Furthermore, a record carrier in which there are no isolated areas because
 all interpositioned areas are initialized may be marked as such, "fully
 ROM drive prepared". A list with boundary areas may also be stored which
 may have to be broadened so as to achieve a greater reliability.
 Operational circumstances during a subsequent session of the relevant
 record carrier in the writing device permitting, these broadenings may be
 performed by further initializing the boundary areas. Moreover, when
 status and/or use information is stored, this information may be doubly
 fixed so as to have a reserve copy of these important data in case of
 damage of the first storage area.
 The system control unit is adapted to initialize the non-written boundary
 areas and, to this end, writes dummy information via write head 42 on the
 basis of the track structure after positioning. The dummy information is
 preferably organized as ordinary information blocks with the associated
 header and address information. For example, zeros are used as contents.
 In a first embodiment, the non-written boundary area 31 preceding an area
 in use is initialized. A short run-in area 33 may then be written, which
 is formed by one or more information blocks, or a width of a band-shaped
 area may be written, as described with reference to FIG. 3. The system
 control unit may also be adapted to write the entire non-written area
 preceding the area which is in use, with the entire area always being
 written from the minimal radius up to and including the newly detected
 area in use. This has the advantage that, upon a jump to areas in use, a
 reading device never needs to cross a non-written area. A combination of
 both measures in a phased approach is achieved as follows. The system
 control unit writes the boundary area on at least a run-in length and on a
 larger, tape-shaped area if the operational circumstances allow this.
 Alternatively, at least a band-shaped area may be written, and,
 operational circumstances permitting, the entire area can be filled up
 from the beginning of the area intended for data storage till the most
 remote area being in use. In these combinations, the system control unit
 will thus first write the area to be minimally initialized when an
 instruction to eject the record carrier is given, and will only then
 perform the eject instruction. In a second embodiment, the system control
 unit is adapted to write the non-written boundary area 32 directly after
 the area in use, as described with reference to FIG. 3. A combination of
 writing the boundary area before and after the area in use is desirable.
 It is of course possible to further combine the measures and perform them
 in phases. The reception of a writing instruction is described as an
 example. During positioning, the system control unit detects that a short
 area preceding the addressed area is unwritten by reading the area until
 the desired address is reached. From this point, the system unit writes
 the addressed area with the information received in the writing
 instruction. Subsequently, the system control unit reads the boundary area
 directly following the area which has just been written. After performing
 the actual writing instruction, the system control unit then changes over
 to writing the detected non-written boundary areas. However, the instant
 of doing this can be postponed when a new writing instruction has
 meanwhile been received. The memory can then remember which areas must
 still be initialized. At a later instant, a broader area preceding the
 previously detected non-written area can also be read so as to ascertain
 whether this area is non-written, and this area can subsequently be
 initialized. If it is already known that the area is (non-)written, for
 example from status information read from a record carrier according to
 the invention as described with reference to FIG. 3, a boundary area
 preceding a new area to be put into use can be written directly prior to
 writing the addressed area. This has the advantage that the writing unit
 is positioned only once, after which it successively writes during a
 longer period of time. This is less time-consuming than two or three
 successive writing operations. In a further embodiment, the initialization
 instant is adapted to further operational circumstances. For example, the
 system control unit waits for a fixed period of time with the
 initialization after the last writing or reading instruction has been
 performed so as to enable a host computer to transmit the next instruction
 to the writing device. After this waiting time, the writing device then
 acquires an "idle mode" in which it changes over to the initialization
 operation on its own initiative. When a new writing or reading instruction
 in the idle mode is received, there will be a slightly longer response
 time of the writing device because it will first complete the dummy
 information block which is being written at that moment. A certain part of
 areas still to be initialized may also be considered to be necessary and a
 further part remote from the areas that are in use may be considered to be
 desirable. If there is sufficient time in the idle mode, both categories
 are initialized, but if an instruction for ejecting the record carrier has
 previously been received, then at least the necessary category will as yet
 be initialized. This causes a short waiting time for the user.
 Postponement of the initialization operation until an eject instruction
 has the advantage that a minimal number of areas is initialized. In fact,
 in a session between insertion and ejection of the record carrier, areas
 may first be considered as non-written boundary areas, while they are
 subsequently put into use themselves. Initialization within the session is
 therefore unnecessary and would only cause wear.
 FIG. 5 shows a reading device according to the invention for reading
 information blocks. The reading device is provided with drive apparatus 45
 for rotating the disc-shaped record carrier 1, and a read head 52 for
 scanning the track on the record carrier. The read head 52 is radially
 positioned on the track by positioning means 44 on the basis of signals
 derived from marks on the record carrier. In accordance with the
 conventional Differential Phase Detection or Differential Time Detection
 system (DPD or DTD), for example, the reflected radiation on a detector
 (not shown) can be received. The detector is subdivided into 4
 sub-detectors. By determining phase or time differences between the
 signals of the sub-detectors, the position of the scanning spot with
 respect to the series of marks written in the track can be determined. In
 this respect it may be noted that such a device intended for reading Read
 Only record carriers such as, for example DVD-ROM, will not be provided
 with apparatus for deriving tracking and/or position information from a
 track structure on a rewritable record carrier. During reading, the signal
 from the read head 52 is converted into the information in the reading
 apparatus 43 including, for example, a channel decoder and an error
 corrector. Moreover, the device is provided with a system control unit 46
 which will displace the read head 52 to a radial position, inter alia,
 based on a read command, which position will be at a short distance ahead
 of the area to be read (coarse positioning), and subsequently the system
 control unit will derive the current position via the read head 52 and the
 positioning apparatus 44 from position information read from the record
 carrier and subsequently (precision-)position the read head on the basis
 of the position information. The reading device according to the invention
 is provided with search apparatus for searching a written area if no marks
 can be read during the positioning operation. To this end, the system
 control unit 46 detects after a jump whether there are marks in the area
 where the read head 52 has landed. If no marks are present, the read head
 52 is further displaced via positioning apparatus 44 until marks are
 detected. First, the system control unit can displace the read head in a
 direction in which the information blocks to be read are expected because
 it is attempted in the global positioning operation to position the read
 head ahead of these information blocks. Secondly, in a further embodiment,
 the read head may be displaced in the opposite direction when no marks are
 found in the first direction after a displacement through a predetermined
 distance. This is an advantage when, due to mechanical tolerances or other
 causes, the read head has landed, after a jump, beyond the area to be
 read.
 An embodiment of the reading device is provided with detection apparatus
 for detecting the presence of marks, for example, for detecting the level
 of the high-frequency signal from the detector. After the global
 positioning operation, the read head is displaced at a raised radial speed
 until a written area is found, without having to reproduce information
 from the record carrier via the read apparatus, and without the tracking
 apparatus being in a locked-in state.
 An embodiment of the reading device is provided with apparatus for
 determining the average track pitch. Since the radial distance must be
 computed when a jump is being made, the actual track pitch influences the
 radial position of the area to be read. Generally, the reading device will
 start from the track pitch described in the system specification of the
 relevant record carrier. During the global positioning operation, based on
 a displacement sensor, the accuracy can be improved by comparing the
 deviation between the computed landing position and the actually found
 landing position at previously performed jump instructions, and by
 determining a correction factor therefrom for the computed jump distance
 and the actual jump distance for the next jump. As a result, both a
 possible deviation of the displacement sensor and the deviation of the
 average track pitch of the relevant record carrier are taken into account
 in this correction process when determining the jump distance.
 An embodiment of the reading device is provided with search apparatus which
 include apparatus for detecting track crossings of the beam with tracks in
 non-written areas of the track pattern, and the positioning apparatus are
 adapted for positioning depending upon the detected track crossings. For
 positioning in written areas, DPD or DTD positioning apparatus are adapted
 to detect deviations of the center of the track with respect to the
 scanning spot which is projected via the beam onto the record carrier.
 Upon global positioning in written areas, these deviations can be
 converted in a conventional manner into a count of the number of times the
 scanning spot crosses a track and are therefore a measure of the distance.
 The reading device is now provided with further means for detecting track
 crossings, such as the known Push-Pull detection, with which the track
 structure in non-written areas can be detected. It is not necessary to
 demodulate and decode position information from a modulation as described
 with reference to FIG. 1. By detecting and counting the tracks as
 indicated via the track structure, the distance at a jump is measured, and
 the positioning means are then controlled on the basis of the measured
 distance.
 FIGS. 6 and 7 shows positioner 44 and system drive unit 46 of FIGS. 4 and 5
 in more detail. The purpose of these figures is to illustrate the claimed
 apparatus and they are not required for an understanding of the invention.
 The apparatus and relationships shown in this figure have been previously
 described in this specification, in relation to a specific embodiment of
 the invention, thus this portion of the description will only briefly
 identify the apparatus.
 In FIG. 6, positioner 44 includes: positioning apparatus 61 for
 mechanically positioning the read/write unit; apparatus 62 detects marks
 and track wobble on the record carrier; position control apparatus 63
 generates control signal for controlling the position of the read/write
 unit with respect to the track pattern on the record carrier (i.e. to
 control the positioning motor). The position control apparatus includes
 apparatus 64 for controlling position depending on the marks and on the
 status information (80 in FIG. 7) for the record carrier; apparatus 65 for
 controlling position based on actual average track pitch measured on the
 record carrier; and apparatus 66 for controlling position based on
 detected track crossings during a radial jump.
 In FIG. 7, the system drive unit 46 includes a microprocessor 70,
 programmable memory 71 and ports 72 and 73 for receiving information and
 providing control signals and information. Memory 71 includes programmed
 apparatus for controlling the operation of CPU 70 and a copy of
 information that has been read or will be written to the record carrier,
 and other information required for operations. The programmed apparatus
 include apparatus 74 for detecting areas of the record carrier which are
 in-use for writing information blocks. Apparatus 74 includes: apparatus 75
 for detecting areas in-use based on instructions received by the device
 for writing information; and apparatus 76 for detecting areas in-use based
 on use information 77 which is initially read from the record carrier,
 kept updated in memory, and occasionally written to update the record
 carrier. The programmed apparatus in memory 71 also includes apparatus 78
 for detecting non-written boundary areas adjoining the areas which are
 in-use, and including apparatus 79 for detecting non-written boundary
 areas based on status information 80 initially read from the record
 carrier, kept updated in memory, and occasionally written to update the
 record carrier. The status information includes information 81 indicating
 the written or non-written state of areas on the record carrier.
 Memory 71 also includes initialization apparatus 90 for writing dummy
 information into non-written boundary areas adjoining areas in-use for
 writing information blocks to the record carrier. The initialization
 apparatus includes: apparatus 91 for writing to boundary areas preceding
 areas in-use for writing information; apparatus 92 for writing to boundary
 areas subsequent to areas in-use for writing information; apparatus 93 for
 controlling the width of areas written with dummy information preceding or
 subsequent to areas in-use for writing information blocks; apparatus 94
 for writing dummy information adjacent to an area immediately prior to
 writing information blocks to the area; and sequent apparatus 95 for
 writing dummy information subsequent to receiving a write instruction.
 Subsequent apparatus 95 includes: apparatus 96 for writing dummy blocks
 when no writing instructions have been received for a sufficient period;
 and apparatus 97 for writing dummy blocks when an ejection instruction or
 an instruction to turn off instruction has been received. The
 initialization apparatus further includes apparatus 98 for detecting
 status information on the record carrier about the status of areas.
 The device includes apparatus 100 of reproducing status information 80. A
 second copy on the record carrier assures that it will be available if a
 portion of the record carrier is corrupted. Also, the status information
 and the use information for the disk is read from the record carrier and
 is preferably kept in a memory of the device for fast access.
 The device also includes programmed search apparatus 110 to search to
 displace the reading unit in a radial direction for finding the beginning
 of a area desired to read from or write information. The search apparatus
 includes: apparatus 111 to search after making a jump to position
 predicted to be just before the desired area; apparatus 112 to limit the
 amount of forward searching, and apparatus 113 for searching in a previous
 area to the position to which the device jumped. The search apparatus also
 includes apparatus 114 for determining the actual track pitch of the
 record carrier; and apparatus 115 for counting the number of tracks
 crossed during a radial jump including tracks in unwritten areas.
 Positioner control apparatus 63 may be provided within the system drive
 unit memory as shown or within the positioner apparatus 44 as shown in
 figure, or in another location in the device, or portions of the
 positioner control apparatus may be provided in one location and other
 portions provided in another location.
 Memory 67 may be dynamic random access memory or non-volatile memory. The
 above specific embodiment with programmed devices may be implemented by
 reading programs and information from the record carrier 1 through ports
 72 or 73, into memory 71. Alternatively the devices may be implemented by
 connecting a memory component 116 communicating with CPU 66 such as by
 inserting a memory cartridge into a slot or a non-volatile memory package
 into a socket.
 The reading and/or writing device of the invention may include a
 programmable computer system or computer network. FIG. 8 shows computer
 system 120 and programmable computer system 121 with a read and/or write
 unit 122, a read unit 123 and a positioner 124 communicating through a
 communications network 122. Computer 120 includes apparatus 123 for
 programming computer 121 for implementing the inventions of this
 application. Computer 120 generates signals transferred through
 communication network 123 to the programmable computer 121 to provide the
 programmed apparatus of the invention. Thus if the read or write unit is
 subsequently connected to computer 122, then the read device and/or write
 device of the invention will be implemented, and the method of the
 invention practiced.
 The invention has been disclosed with reference to specific preferred
 embodiments, to enable those skilled in the art to make and use the
 invention, and to describe the best mode contemplated for carrying out the
 invention. Those skilled in the art may modify or add to these embodiments
 or provide other embodiments without departing from the spirit of the
 invention. Thus, the scope of the invention is only limited by the
 following claims: