Dynamic information storage or retrieval – Storage medium structure – Optical track structure
Reexamination Certificate
2001-11-09
2004-08-10
Patel, Gautam R. (Department: 2655)
Dynamic information storage or retrieval
Storage medium structure
Optical track structure
C369S053210, C369S059250
Reexamination Certificate
active
06775227
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical disk, and more particularly to an optical disk which enables determination as to whether or not it is an optical disk which has been copied in an unauthorized manner.
2. Description of the Background Art
Conventionally, as a method for preventing unauthorized copying of optical disks, a method is commonly used which previously performs a specific process to an optical disk. Specifically, this method utilizes physical features which are formed on an optical disk through the specific process to determine whether it is an authorized optical disk or not. When an optical disk is copied in an unauthorized manner, only the usual data which is recorded on the optical disk will be copied, without performing the aforementioned specific process. Therefore, an optical disk which has been copied in an unauthorized manner lacks the physical features formed by the specific process. When accessing an optical disk, an optical disk drive checks for physical features to determine whether or not the specific process has been properly performed, thereby determining whether it is an optical disk produced in an authorized manner or an optical disk copied in an unauthorized manner. According to the above method, optical disks copied in an unauthorized manner can be prevented from being used.
For example, according to an invention described in Japanese Patent Laid-Open Publication No. 7-282472, a signal pit array is provided between specific tracks, such that the tracks located on the inner and outer periphery sides of the pit array define pitless areas free of pits. In accordance with an optical disk having such features, it is possible to determine whether or not it is an optical disk produced in an authorized manner, based on the presence or absence of randomly-read portions on the optical disk.
According to an invention described in Japanese Patent Laid-Open Publication No. 9-81938, displaced pits are formed in specific positions. In accordance with an optical disk having such features, it is possible to determine whether or not it is an optical disk produced in an authorized manner based on the presence or absence of displaced pits.
In addition to those described in the above two publications, various methods are conceivable as methods for determining authorized disks, e.g., a method utilizing the number, positions, or size of physical features obtained by performing a specific process for an optical disk, or a method utilizing the reflectance when physical features are irradiated with laser light. The determination as to whether an optical disk has been produced in an authorized manner or not is made based on whether the physical features satisfy a certain determination criterion. For example, in the case where determination is made by utilizing the number of displaced pits, the presence of a certain number or more of displaced pits would constitute a criterion for determining an authorized optical disk. In the case where determination is made by utilizing reflectance, the presence of a certain range of reflectance would constitute a criterion for determining an authorized optical disk.
The determination criterion for an authorized optical disk is decided so that any optical disk on which physical features are formed with a predetermined precision or above will be determined as an authorized optical disk. This is in order to ensure that an optical disk having no physical features formed thereon will be determined as optical disk copied in an unauthorized manner, and that an optical disk having physical features formed with a low precision will also be determined as an optical disk copied in an unauthorized manner. The reason is that an optical disk having physical features formed with a low precision can be easily produced, and therefore could also be produced in an unauthorized manner by imitating its physical features.
Moreover, a security level is decided depending on what degree of precision of the formed physical features will be permitted under the determination criterion. Specifically, the security level is lowered by setting a lenient determination criterion, i.e., by permitting optical disks having physical features formed with a low precision. On the other hand, the security level is increased by setting a severe determination criterion, i.e., by only permitting optical disks having physical features formed with a high precision.
Conventionally, the determination criterion for determining an optical disk produced in an authorized manner is previously set in a reproduction apparatus for optical disks. In other words, in order to change the determination criterion, the setting of the reproduction apparatus for optical disks must be changed. However, it is practically impossible to change the setting of the reproduction apparatus for optical disks owned by every user. Therefore, conventionally, the determination criterion for determining an optical disk produced in an authorized manner is fixed and cannot be changed.
In the actual production of optical disks, it may become necessary to change the security level. For example, consider the case where the security level is to be lowered. By lowering the security level, even optical disks having physical features formed with a low precision will be permitted as optical disks produced in an authorized manner. Setting a low security level results in an increased yield and improved productivity. Therefore, the security level may be set low in the case where productivity is regarded as important, e.g., when it is intended to reduce the production cost or produce large quantities over a short period of time. On the other hand, depending on the value of the contents, a high security level may be set in order to prevent unauthorized copying as much as possible. Furthermore, in the case where a currently-set security level can no longer prevent unauthorized copying, it will be necessary to increase the security level in order to cope with the unauthorized copying. Thus, it would be desirable to employ a changeable security level so as to allow a security level to be set in accordance with the purpose.
Conventionally, however, it is impossible to change the security level because the determination criterion cannot be changed. Therefore, once a security level is set, it cannot be changed later, so that it is impossible to set a security level depending on the purpose.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide an optical disk which allows the security level against unauthorized copying to be easily changed.
The present invention has the following features to attain the object above.
A first aspect of the present invention is directed to an optical disk subject to determination by an optical disk reproduction apparatus as to whether it is an optical disk produced in an authorized manner or not, the optical disk comprising a feature forming area and a criterion recording area. The feature forming area has formed therein a physical feature to be used by the optical disk reproduction apparatus for determining whether it has been produced in an authorized manner or not. The criterion recording area has recorded therein a determination criterion by which it is determined as having been produced in an authorized manner if the physical feature is formed with a predetermined precision or above.
In accordance with the above configuration, a determination criterion is recorded on an optical disk for determining whether it has been produced in an authorized manner or not. The determination criterion can be changed by changing the information which is recorded on the optical disk. This can be easily done because there is no need to change the setting of the optical disk reproduction apparatus. Therefore, the security level against unauthorized copying can be easily changed by changing the determination criterion. As a result, the security level may be lowered for improved optical disk productivity, e.g., in the case where the
Nishiumi Satsoshi
Watanabe Atsushi
Nintendo Co. Ltd.
Nixon & Vanderhye P.C.
Patel Gautam R.
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