WO2008135884A1

WO2008135884A1 - Optical disc for long-term storage

Info

Publication number: WO2008135884A1
Application number: PCT/IB2008/051600
Authority: WO
Inventors: Tony P. Van Endert
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2007-05-03
Filing date: 2008-04-25
Publication date: 2008-11-13
Also published as: TW200912900A

Abstract

An optical storage disc (1) for archiving purposes comprises a storage space (10) with an administrative section (12) and a user-accessible section (11) for writing data. At least the storage space (10) of the storage disc (1) is made of a phase change material which undergoes a reversible phase change during an optical writing process, and the administrative section (12) of the storage space (10) contains disc type information indicating the disc as a Write Once type of disc (DVD+R, DVD-R, BD+R, BD-R). Thus, the disc has the physical properties of a rewritable disc (DVD+RW, DVD-RW, BD-RE), but is treated by disc drive devices as being a Write Once type of disc. Thus, the disc combines long lifetime reliability with overwrite protection.

Description

Optical disc for long-term storage

FIELD OF THE INVENTION

The present invention relates in general to the storage of data.

BACKGROUND OF THE INVENTION Storage of data can be done by writing data to a storage medium, of which magnetic and optical storage media are well known. In terms of storage capacity, optical discs are preferred over magnetic discs.

As regarding the purpose of the storage, it is possible to make a distinction between short-term storage and long-term storage. Short-term storage means storage where it can be expected that the stored data is read back at a relatively short time after storage, for instance within one year. Examples of such short-time storage are private or office work documents, or a movie that is recorded now for playback at a later time. Long-term storage is meant for the situation where important data are to be stored for decades, typically for 30 years and longer, to be retrieved in a case of need only. Storing items in this way can be compared to putting an item in an archive. Examples can include the first photos or film footage made from a newly-born, or a scanned copy of an important agreement.

It is possible to store a data item for a longer period using short-term storage facilities; in that case, the data item should be retrieved and restored on a regular basis, for instance once every 5 years or even once every year to be on the safe side. In the case of long-term storage, it is intended that the storage medium is placed in a (preferably secure and conditioned) location where it stays for many years without being retrieved. Since it is obviously desirable that no data is lost over the years, the storage medium must be highly reliable. Also in terms of reliability, optical discs are preferred over magnetic discs.

Optical discs have been developed in several types. Over the years, new technologies and standards have been developed, resulting in an enormous increase of storage capacity. For example, in order of increasing capacity, the standards of CD, DVD, BD have been developed.

On another level, optical discs have been developed with a view to possibilities of use. For example, the types of Read Only, Write Once, Rewritable have been developed. Discs of Read Only are mainly used for retail of music, movies, computer software, computer games, etc. Writable discs are used for allowing consumers to store their data. Obviously, Read Only discs are not suitable for general archiving purposes.

Writable discs are Write Once or Rewritable, depending on the physical mechanism used to store the data. While it is noted that the technology of optical data storage is known per se and an extensive explanation is not needed here, it is noted that the main difference between Write Once and Rewritable lies in the reversibility of the changes in the material of the disc as occurring in the writing process. In a commonly used type of DVD Write Once optical disc, the material of the blank disc comprises a dye material; under influence of laser radiation, the dye is irreversibly destroyed. In the case of Rewritable discs, the discs are made from a material having a crystalline structure, which undergoes a reversible phase change to an amorphous structure in the writing process; by applying a different laser power, the material can be made crystalline again so that the data is erased.

SUMMARY OF THE INVENTION

In general, Rewritable discs have a higher reliability than Write Once discs. Although it is possible to make very high quality Write Once discs with a life expectancy of 25 years, this appears to be very difficult, and in practice there are found discs with a life expectancy in the order of 1 year or even less. In contrast, standard Rewritable discs have a life expectancy in the order of 30 years or better. This would make Rewritable discs better suitable for archiving purposes as compared to Write Once discs. However, in the case of Rewritable discs, there always is a possibility that the data is overwritten or erased during the storing period.

An object of the present invention is to provide an optical disc for archiving purposes.

More particularly, an object of the present invention is to provide an optical disc combining the reliability of a Rewritable disc with the intrinsic overwrite protection of a Write Once disc.

According to the present invention, the above objective is attained by providing an optical disc made from a phase change material but containing identification information identifying the disc as a Write Once disc.

Further advantageous elaborations are mentioned in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS These and other aspects, features and advantages of the present invention will be further explained by the following description of one or more preferred embodiments with reference to the drawings, in which same reference numerals indicate same or similar parts, and in which: Fig. 1 schematically shows an optical disc;

Fig. 2 schematically illustrates the storage space of the optical disc; Fig. 3 is a graph showing laser power as a function of time.

DETAILED DESCRIPTION OF THE INVENTION Figure 1 schematically shows an optical disc 1 having a track 2 where data can be stored. The optical disc is made of a phase change material. A data writing process, which involves irradiating a spot by a laser beam, locally induces a phase change from crystalline to amorphous. Materials of this type, and optical discs made of this type of material, are known per se, for instance DVD+RW, DVD-RW, BD-RE, so a more detailed description will be omitted here.

Figure 2 is a diagram schematically illustrating the storage space 10 of the optical disc 1 as a longitudinal ribbon. Storage locations in the storage space 10 have predefined addresses (Address In Pre-groove, ADIP), but this is not illustrated. The diagram illustrates that the storage space 10 is divided into at least two sections, i.e. a user section 11 and an administrative section 12. The user section 11, also indicated as data area, is the part of the storage space 10 available for writing user data. The administrative section 12, also indicated as Lead-in area, is not accessible to a user.

The administrative section 12 of the storage space 10 contains administrative data, arranged in the administrative section 12 by the disc manufacturer during the manufacturing process of the disc 1 (pre-embossing in pre-groove). The administrative data includes data identifying the disc manufacturer, data identifying the disc type, and data defining an optimum write strategy, including the optimum or maximum write speed. In the following, the disc type information parameter will be indicated as DTI.

For example, according to the DVD+R specification, the administrative section 12 contains a Control Data Zone block, which in turn contains a Physical Format Information block, which a Disc Structure byte. Bit 0 of the Disc Structure byte indicates whether the disc is a Read-Only disc (bit=l) or not (bit=O). Bit 1 of the Disc Structure byte indicates whether the disc is a Recordable (Write-Once) disc (bit=l) or not (bit=O). Bit 2 of the Disc Structure byte indicates whether the disc is a Rewritable disc (bit=l) or not (bit=O). Thus, the Disc Structure byte corresponds to the DTI. DTI = (xxxxxOlO) corresponds to a Recordable (Write-Once) disc, while DTI = (xxxxxlOO) corresponds to a Rewritable disc.

The collection of administrative data, applied during the manufacturing process, will be indicated as stamper. The administrative data also includes the first address where data can been written. In use, a disc drive apparatus (not shown) receiving a new disc will first read the administrative data to adapt its operation in accordance with the administrative data. Since this use of administrative data in an administrative storage section 12 is standard practice, a more elaborate explanation will be omitted here.

From the administrative date, a disc drive apparatus learns how it should operate for handling the specific disc. Operation in the case of a Rewritable disc differs from the operation in the case of a Write Once disc. This is illustrated in figure 3, which is a graph showing laser power (vertical axis) as a function of time (horizontal axis) for the case of a DVD+R disc (3A) and for the case of a DVD+RW disc (3B). In the case of a DVD+R disc, the laser power is normally equal to or close to zero (no write pulse or bias level Pb)), as shown by line portion 31 , while in the case of a write pulse the laser power is pulsed at a relatively high frequency, as shown by line portion 32, so that the laser power is alternated between said normal low level and a high level. The pulse shape is a block shape. This applies to speeds up to 4x; for speeds of 4x and higher, a different pulse shape is used. In the case of a DVD+RW disc, the laser power has a constant erase value well above zero level, as shown by line portion 33, while in the case of a write pulse the laser power is pulsed at a relatively high frequency, as shown by line portion 34, so that the laser power is alternated between zero and a high level.

When a disc is entered into a disc drive writer apparatus, the disc drive apparatus will perform an initialization procedure, which includes reading the DTI parameter. On the basis of the information read, the disc drive apparatus will decide which write strategy to use.

In a standard disc made of a phase change material, the DTI parameter in the administrative section 12 will have a value indicating RW type, so the disc drive apparatus will perform a writing strategy as illustrated in figure 3B. In the disc 1 proposed by the present invention, the DTI parameter in the administrative section 12 has a value indicating R type. Thus, the disc drive apparatus will treat the disc as being a Write Once disc. As a consequence, the disc drive apparatus will not attempt to write to a storage address where data has already been stored: this effectively constitutes an overwrite protection for the RW disc. Further, the disc drive apparatus will perform a pulsed writing strategy as illustrated in figure 3A. Although this writing strategy differs from the writing strategy specifically intended for RW discs, as illustrated in figure 3B, the writing strategy has large similarities with the writing strategy specifically intended for RW discs. Basically, the only substantial difference is the lacking erase level 33. But, since the disc 1 is written only once (thanks to the effective overwrite protection), there is no previously stored data to erase, so the missing erase level 33 does not lead to problems.

Preferably, the administrative section 12 contains write strategy information indicating a writing speed of less than 4x, so that the writing disc drive will use a "pulsed" R type write strategy as illustrated in figure 3 A. It is noted that such "pulsed" R type write strategy is suitable for writing an RW type of disc, as illustrated in figure 3B.

Importantly, the RW disc 1 according to the present invention, being written by the "pulsed" R type write strategy illustrated in figure 3 A, can still be read by a normal disc drive apparatus.

Summarizing, the present invention provides an optical storage disc 1 for archiving purposes, comprising a storage space 10 with an administrative section 12 and a user-accessible section 11 for writing data. At least the storage space 10 of the storage disc 1 is made of a phase change material which undergoes a reversible phase change during an optical writing process, and the administrative section 12 of the storage space 10 contains disc type information indicating the disc as a Write Once type of disc (DVD+R, DVD-R, BD-R). Thus, the disc has the physical properties of a rewritable disc (DVD+RW, DVD-RW, BD-RE), but is treated by disc drive devices as being a Write Once type of disc. Thus, the disc combines long lifetime reliability with overwrite protection.

While the invention has been illustrated and described in detail in the drawings and foregoing description, it should be clear to a person skilled in the art that such illustration and description are to be considered illustrative or exemplary and not restrictive. The invention is not limited to the disclosed embodiments; rather, several variations and modifications are possible within the protective scope of the invention as defined in the appending claims.

For instance, while it is possible that a standard R stamper is used for the information in administrative section 12, it is possible that a standard RW stamper is used, only the DTI parameter "RW" being changed to "R".

Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. 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. A computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems. Any reference signs in the claims should not be construed as limiting the scope. In the above, the present invention has been explained with reference to block diagrams, which illustrate functional blocks of the device according to the present invention. It is to be understood that one or more of these functional blocks may be implemented in hardware, where the function of such functional block is performed by individual hardware components, but it is also possible that one or more of these functional blocks are implemented in software, so that the function of such functional block is performed by one or more program lines of a computer program or a programmable device such as a microprocessor, microcontroller, digital signal processor, etc.

Claims

CLAIMS:

1. Optical storage disc (1) for archiving purposes, comprising a storage space (10) with an administrative section (12) and a user-accessible section (11) for writing data; wherein at least the storage space (10) of the storage disc (1) is made of a phase change material which undergoes a reversible phase change during an optical writing process, and wherein the administrative section (12) of the storage space (10) contains disc type information indicating the disc as a Write Once type of disc (DVD+R, DVD-R, BD-R).

2. Optical storage disc according to claim 1, wherein the administrative section (12) of the storage space (10) contains a stamper associated with a Write Once type of disc (DVD+R, DVD-R, BD-R).

3. Optical storage disc according to claim 1, wherein the administrative section (12) of the storage space (10) contains write strategy information indicating a writing speed of less than 4 times a standard speed.

4. Method for writing information to a Rewritable optical storage disc (1), wherein a pulsed write strategy for Write Once discs is used.

5. Method for providing overwrite-protection to a Rewritable optical storage disc (1), the method comprising the step of giving the disc disc type information (DTI) indicating a Write-Once disc.