REWRITABLE DATA STORAGE MEDIUM

Abstract: The rewritable data storage medium (1) has a rewritable recording layer (9) provided with a tracking structure (8). Said layer (9) has a data recording area (5). An erasable identification mark is present in an identification mark area (4, 4') other than the data recording area (5). The data recording area (5) has a first tracking structure (8'), whereas the identification mark area (4, 4') is substantially free from a tracking structure or has a second tracking structure (8") substantially different from the first tracking structure (8'). Thus erasure of the identification mark is practically impossible, because the location of the erasing spot of a recorder cannot be controlled precisely in radial direction.

Description: Rewntable data storage medium The invention relates to a rewntable data storage medium, having a rewntable recording layer provided with a tracking structure having tracks, said layer having a data recording area, and an erasable identification mark which is present in an identification mark area other than the data recording area and which extends over a radial width of several tracks of the tracking structure in the data recording area. Said rewntable data storage medium is known from Japanese patent application JP-09073666-A The known medium is an optical recording medium Optically readable patterns are wntten outside the data recording area of the recording layer The patterns are readable with the naked eye or by machine and may serve as an identification mark Rewntable data storage, and particularly rewritable recording in optical recording media, is currently finding increasing use in the high-density storage of large quantities of data In the optical recording medium, the information is retneved through the interaction of a radiation beam, e g a focused laser beam, with the optical recording medium A recently introduced type of optical storage medium has the capability to have information recorded on the medium after its manufacture In addition, at a later time, the stored information can be erased or modified This type of optical storage medium, in the disc embodiment, is generally referred to as an erasable or a rewntable optical storage disc Examples are CD-rewntable (RW), DVD-RW, DVD+RW, DVD-random access memory (RAM), and digital video recording (DVR)-red and blue disc, where red and blue refer to the wavelength of the radiation beam, e g recording and reading laser beam The rewritable optical lecord g disc has a recording layer that is responsive to radiation having a relatively high power level The impinging radiation changes properties of the recording layer These property changes aie detected optically through the interaction with an impinging radiation beam of relatively low power level and data encoded by means of the property changes can be recovered For example intensity or polanzation changes of the reflected ladiation may be detected by a photo diode and converted into electncal signals The electncal signals are subsequently converted to a format, which can be conveniently manipulated by a signal processing system In order to provide copy protection secunty for the data stored on a storage medium, a need has been felt for a technique for providing an optical storage medium which has an identification mark This identification mark is applied to every piece of storage medium, e g optical disc The identification mark may for example be a bar code, representing a senal number Dunng recording of copy-protected content, the data is encrypted with a key that is based on this identification mark This prevents so-called bit copying or cloning of the disc Examples are copy protection for recordable media (CPRM) for DVD-RAM and possibly DVD RW Dunng copying of the encrypted content, which is present in the data recording area, the identification mark of the original is not copied to the target medium The empty target medium has another identification mark, which already was applied to it dunng its manufacture A player which reads the cloned medium is not able to construct the correct onginal decryption key, since it is necessanly based on the identification mark of the clone, which is not the correct identification mark belonging to the copied content In order to place the correct identification mark of the original disc, a hacker first has to erase the identification mark of the empty disc and subsequently to wnte an identification mark that corresponds to the encrypted data An important requirement of the identification mark is that it can be applied to the recordable/rewntable media at low cost, dunng the manufactunng process A possibility is the ablative wnting of an unerasable identification mark, e g a "bar-code"-style mark, by means of a YAG laser in the so called Burst Cutting Area (BCA) from radius 22 3 to 23 5 mm, as proposed for DVD -ROM Such a laser is hardly used because of its cost and the risk of contamination due to the ablative wnting with such a laser An alternative is the Narrow Burst Cutting Area (NBCA), which is feasible for CD-RW, DVD-RW, DVD+RW, DVD- RAM and DVR red or blue This NBCA covers a relatively narrow zone, e g from radius 22 7 to 23 5 mm, for wnting an erasable identification mark compared to the non-erasable identification maik in the BCA A phase change recording layer, which is used for these media, can be applied by vapor depositing or sputtenng The recording layer thus deposited is amorphous and exhibits a low reflection In order to obtain a suitable recording layer having a high leflection, the data recording area of this layer must first be completely crystallized, which is commonly referred to as initialization, and which takes place in the final phase in production of each medium This is performed in a production apparatus called an initializer, in which a laser beam scans and heats the moving recording layer to a temperature below its melting temperature but above its recrystal zation temperature, causing the amorphous recording layer to crystallize. This production apparatus crystallizes a path that has a radial width of many tracks of the tracking structure. The whole data recording area must be crystallized which is accomplished by moving the initializer beam in radial direction while rotating the medium. However, at the inner and the outer regions of the disc, e.g. for DVD+RW within a radius of 23.5 mm and beyond a radius of 58.5 mm, the disc may be partially crystallized by using a pulsed laser beam m the initializer. So an identification mark, e.g. bar code pattern, may be wntten outside the data recording area By starting the pulse sequence locked to the revolution of the disc and rotating the disk in constant angular velocity (CAV) mode, the identification mark is wntten on the disc Production costs are negligibly small, because the identification mark is wntten dunng initialization and adds only a few percent of time to only this process step. The identification mark is erasable because it is wntten using the same or the inverse property change of the recording layer as is used for user data recording. The optical quality and the uniformity of the layers of the disc within 23.5 mm and beyond 58 5 mm is generally worse than in the data recording area. Therefore, it is preferred to use a low-density pattern in order to have reliable detection. Generally the initialization laser beam is rectangle-shaped and measures approximately 1 micrometer in tangential direction and 100 micrometers in radial direction. Wnting an identification mark has been demonstrated for DVD-RW and DVD+RW. Since wnting an identification mark is part of the already required initialization step, it is an attractive and economic method. According to said Japanese application an identification mark is wntten dunng initialization, as in the descnption above, of a phase change type rewntable optical recording medium It is a disadvantage of the known medium descnbed in said application that a consumer optical disc recorder can erase the identification mark relatively easily Such a recorder contains a wnte laser that may be used to erase, overwrite or change the identification mark The identification mark is wntten in an area that is accessible for read out by a consumer recorder. By changing the firmware controlling the recorder dnve and by positioning the laser wnte/read head, the identification mark may be erased by moving the write/read head to the exact position of the identification mark, and another identification mark may be written belonging to the illegally copied content of a source disc. In such a manner a hacker may bypass the copy protection function of the identification mark It is an object of the invention to provide a data storage medium of the kind descnbed in the opening paragraph in which the erasure of an identification mark by a consumer apparatus suitable for recording on, rewntmg on and reading from a data storage medium is counteracted This object is achieved m that the data recording area has a first tracking structure, whereas the identification mark area is substantially free from a tracking structure or has a second tracking structure substantially different from the first tracking structure Due to the absence or modification of the second tracking structure in the identification mark area, erasure of the identification mark by a consumer recorder is counteracted and tracking of the laser head and performing an erasing action consistently for several tracks in the same manner as in the data recording area is generally impossible The identification mark usually spans a distance in radial direction, which corresponds to hundreds of tracks of the tracking structure in the data recording area In this document, the word several may signify anything in the range from a few to hundreds In a favorable embodiment the identification mark area is substantially free from a tracking structure The tracking structure, or any other means used to "guide" the wnting head dunng recording, is very shallow or even absent The tracking structure of the data recording area may partially be present in the identification mark area, e g adjoining the data recording area, and abruptly stop when e g moving radially inward This is a very elegant and easily implemented embodiment of the medium according to the present invention A consumer recorder is generally not able to tiack in the identification mark area, so that consistent wnting or erasing is almost impossible Because a consumer recorder wnting spot typically has a diameter of approximately 0 5 to 1 micrometer it can not erase the identification mark, which e g may be 0 8 mm wide in radial direction, m a single revolution of the disc The recorder would have to erase consistently for hundreds of revolutions, while moving the laser head in a radial direction The laser head in the recorder can only turn approximate circles relative to the disc, because the identification mark area is substantially free from a tracking structure Due to the fact that there are always tolerance deviations in both the disc, and the head-positioning mechanism, the laser spot can not or hardly erase/rewnte the identification mark fully and consistently Because only approximate circles are described dunng read out of the identification mark, the width of said mark will necessarily span the total available space, e g 0 8 mm in radial direction, of the identification mark area in order to cope with these tolerances. Dunng reading of the identification mark, the absence of a tracking structure in the identification mark area is no problem because the player puts its read head roughly, at a predefined position, in the middle of the identification mark area, and revolves the disc once, reading the reflectivity change, or any other detectable property, in the meantime. Since the identification mark may have a low spatial frequency compared to the user data, e.g. only a few hundred bits in the single revolution, it is no problem when the curve descnbed by the read-out spot deviates from an ideal circular shape, e g. is eccentnc. In another embodiment the second tracking structure compnses at least one track the shape of a spiral groove that is interrupted at at least one location When, in the identification mark area, this spiral is interrupted the read/wnte head will "loose" tracking and consistent erasure or wnting of an identification mark is almost impossible. Preferably the spiral is interrupted at vanous locations, which causes the laser head to "loose" tracking frequently. Such a modified tracking structure can be obtained relatively easily by interrupting the laser that is used in the manufacture of the tracking structure in the same manner. In another embodiment the second tracking structure compnses a plurality of tracks in the shape of concentnc grooves. When concentnc grooves are used instead of a spiral, the laser beam remains in one concentnc groove dunng tracking. Because the concentnc groove is closed into itself, the position of the laser head, generating the laser beam, does not change in a radial direction relative to the disc, while tracking. The wnte laser beam of a consumer recorder dnve erasing or wnting into the identification mark area, follows the groove back into itself, much like a needle at the very end of the former 45 rpm vinyl record. Due to the concentnc grooves, the consumer disc recorder cannot erase the identification mark that e.g. spans at least a few hundred tracks Erasure of a fraction of the identification mark above one concentnc groove is possible but the remaining portion of the identification mark above the adjacent concentnc grooves remains intact. It is extremely difficult, or almost impossible, for a consumer to position the laser beam in every concentnc groove containing a portion of an identification mark. Read out of the identification mark is performed as descnbed above when the identification mark area is substantially free from a tracking structure. However, dunng read out of the identification mark, it may be advantageous to put the read head in tracking mode This has as its result that the radial width of the identification mark may be much smaller, e g only a few tens of tracks. It is then assumed that this narrower identification mark is wntten dunng manufacture of the disc while a special head that wntes the identification mark is subsequently tracking in several concentnc grooves This requires a special tracking servo system that is not available in a consumer recorder Many combinations of zones with and without tracking structures are possible Even zones with tracks which are identical to those used in the data recording area may be present in the identification mark area Especially the zone adjoining the data recording area may still contain some tracks that are identical to those used in the data recording area It is even possible to wnte the identification mark at the outer radius of a rewntable data storage medium outside the data recording area with all the vanations of embodiments descnbed in this document In a refinement of the embodiments at least one track of the second tracking structure is modulated with address information This address information can be an encoded radial position number, a track number or another reference signal Examples of encoded address information in a tracking structure are a phase or frequency modulated track wobble and relatively shortly interrupted grooves with pit headers The latter does not cause the laser head to loose tracking The advantage of such address information is that a read wnte head of a production apparatus, by reading the address information, can determine its position on the medium precisely and that dunng production of the data storage medium according to the invention the wnting of the identification mark can be performed in a well defined location Special hard- and software in a production apparatus enables wnting of an identification mark in modified tracking structures, e g concentnc or interrupted spiral grooves with address information Extra production time is relatively low compared to the total production time of the medium E g wnting 20 tracks with an identification mark does not require more than 1 sec of time at a typical rotation speed of 25 Hz It is emphasized that the special hard- and software in the production apparatus is not available in a consumer recorder that therefore will not be able to erase or wnte an identification mark The recording layer generally compnses a matenal being able to change between an amorphous and a crystalline state and the recorded information in the recording layer generally is optically readable Presently, this is the most widely used technique for rewntable optical recording In an embodiment the recording layer comprises a magnetic matenal being able to change between a first and a second magnetization state The recorded information in the recording layer is magnetically and/or optically readable Read out of the magnetic state of the magnetic recording layer may be performed with a magnetic read head which floats closely above said magnetic recording layer. Read out of the magnetic state of the magnetic recording layer may also be performed optically by detecting a small rotation of the linear polanzation state of an impinging laser beam after reflection at the magnetic recording layer surface. The direction in which rotation of the polanzation occurs depends on the local magnetic field, e.g. magnetization state, of the recording layer. This effect is known as Kerr rotation. The invention is applicable to all kinds of rewritable media in which a property of the recording layer can be changed reversibly and in which a tracking structure is used to guide a read and wnte device which generates physical energy in order to record or read said property changes. The descnption of the drawings given hereafter relates to a rewntable optical recording medium, having an amorphous and a crystalline state recording layer, but this is not a limitation. Embodiments of the data storage medium according to the invention will be descnbed with reference to the drawings. It should be noted that drawings are not to scale For instance track distances are drawn much larger than they generally are. In the drawings: FIG. l schematically shows the top view of the data storage medium in which a central area 20 is indicated which is shown enlarged in FIGS 3 to 5 FIG 2 shows a cross section along the line II-II as indicated in FIG. l of the data storage medium representing the embodiment of FIG 5 FIG 3 shows an enlarged view of the square area 20 of FIG.l of the data storage medium representing a first embodiment FIG 4 shows an enlarged view of the square area 20 of FIG.l of the data storage medium representing a second embodiment FIG.5 shows an enlarged view of the square area 20 of FIG.l of the data storage medium representing a third embodiment In FIGS 1 and 2 a rewntable data storage medium 1 is shown, which has a rewntable recording layer 9 provided with a tracking structure 8 having tracks The recording layer 9 has a data recording area 5, and an erasable identification mark 3 which is present in an identification maik area 4 other than the data recording area 5 The identification mark 3 o extends over a radial width of several hundred tracks of the tracking structure 8 in the data recording area 5. The data recording area 5 has a first tracking structure 8', whereas the identification mark area 4 is substantially free from a tracking structure or has a second tracking structure 8" substantially different from the first tracking structure 8'. The rewntable data storage medium 1 may be an optical data storage medium which has a rewntable recording layer 9 consisting of material being able to change between an amorphous and a crystalline state. These types of storage media are generally referred to as phase change type optical recording discs The storage medium has a center hole with an inner penphery 2 The recording layer 9 is present between a circle, indicated with reference numeral 10, and the outer penphery 13. In area 5, between circles indicated by 11 and 12, a first tracking structure 8' is present which is used to guide a laser wnte/read head for wnting/erasing data in the data recording area 5 by an end user of the optical data storage medium 1 Another possibility is that dunng production of the medium 1 data, e.g licensed software which may be sold together with the medium 1 to an end user, is recorded in area 5 Area 4, between circles indicated by 10 and 11, contains an identification mark 3 that is wntten dunng production of the data storage medium 1. The identification mark 3 consists of areas with low and high optical reflection, which correspond to the respective amorphous and crystalline state of the recording layer 9 The identification mark 3 may also be present in area 4' between radius 12 and the outer penphery 13 of the disc, in which case the descnptions of tracking structures given for area 4 are applicable accordingly. The identification mark 3, e.g. a bar code, may represent a senal number. Dunng recording of copy-protected content by a manufacturer in area 5, the data is encrypted with a key that is based on this senal number. Data can only be decrypted when the serial number, represented by the identification mark, corresponds to the key of the data In FIG. 3 the identification mark area 4 is substantially free from a tracking structure. The identification mark area 4 may still contain a portion, e g adjoining the data recording area 5, with a continuation of the first tracking structure 8^ of the data recording area An identification mark 3 is present in the identification mark area 4 The absence of a tracking structure in the major portion of the identification mark area 4 prevents tracking of the laser read/wnte head of an optical recorder and consistent erasure of the identification mark 3 In FIG 4 the second tracking structure 8f compnses at least one track 6 in the shape of a spiral groove that is interrupted at at least one location. In this embodiment a spiral groove is interrupted at seveial locations Tracking by the laser read/write head is not possible m the interrupted areas and thus consistent erasure of the identification mark 3 is counteracted. In FIG 5 the second tracking structure 8" compnses a plurality of tracks 6 in the shape of concentnc grooves. The laser read/wnte head will remain locked in one concentnc groove dunng tracking. The fraction of identification mark 3 just above this concentnc groove can be erased but the major portion of the identification mark 3 above all other concentnc grooves and non-grooved areas remains intact. It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word "compnsing", "compnse" or "compnses" does not exclude the presence of elements or steps other than those listed in a claim The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage According to the invention an erasable data storage medium is provided, which has an erasable identification mark which is present in an identification mark area other than the data recording area. The data recording area has a first tracking structure, whereas the identification mark area is substantially free from a tracking structure or has a second tracking structure substantially different from the first tracking structure, by which erasure of the identification mark by a consumer data storage recorder is counteracted

Claims: CLAIMS. 1. A rewntable data storage medium (1), having a rewntable recording layer (9) provided with a tracking structure (8) having tracks, said layer (9) having a data recording area (5), and an erasable identification mark (3) which is present in an identification mark area (4) other than the data recording area (5) and which extends over a radial width of several tracks of the tracking structure (8) in the data recording area (5) charactenzed in that the data recording area (5) has a first tracking structure (8'), whereas the identification mark area (4) is substantially free from a tracking structure or has a second tracking structure (8") substantially different from the first tracking structure (8') 2. A rewntable data storage medium (1) as claimed in claim 1 charactenzed in that the second tracking structure (8") compnses at least one track (6) in the shape of a spiral groove that is interrupted at at least one location 3 A rewntable data storage medium (1) as claimed in claim 1 charactenzed in that the second tracking structure (8") compnses a plurality of tracks (6) in the shape of concentnc grooves 4 A rewntable data storage medium as claimed in claim 2 or 3 characterized in that at least one track (6) of the second tracking structure (8") is modulated with address information 5 A rewntable data storage medium as claimed in claim 1, 2, 3, or 4 charactenzed in that the recording layer (9) compnses a magnetic matenal being able to change between a first and a second magnetization state, and the recorded information in the recording layer (9) is readable in a manner selected from magnetically and optically

Inventors: BRONDIJK ROBERT A, DRENTEN RONALD R, SPRUIT JOHANNES H M, TALSTRA JOHAN C, BRONDIJK, ROBERT, A., DRENTEN, RONALD, R., SPRUIT, JOHANNES, H., M., TALSTRA, JOHAN, C.
Applicants: KONINKL PHILIPS ELECTRONICS NV, KONINKLIJKE PHILIPS ELECTRONICS N.V.
Application year: 2001
Main classification: G11M
IPC codes: G06F3, G11B7, G11B11, G11B19, G11B20