Dynamic information storage or retrieval – Condition indicating – monitoring – or testing
Reexamination Certificate
1999-04-01
2002-04-23
Hindi, Nabil (Department: 2651)
Dynamic information storage or retrieval
Condition indicating, monitoring, or testing
C369S275300, C369S053200, C369S053240
Reexamination Certificate
active
06377526
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to optical storage media, and in particular to an optical write once-read many (WORM) optical medium which may also be fully physically erased and re-written.
Optical media for storing data are well-known in the art. The great advantage of such optical storage media is the very high storage capacity (on the order of 10
11
bits of data, or the equivalent of forty reels of magnetic tape).
These characteristics of optical media make them ideal for storing large amounts of data which must be retained for a long time, but is seldom accessed. For example, optical media are frequently used for the storage of tax records, which must be kept for several years.
Non-erasable, or write-once, optical data storage media have a plurality of bit positions, each of which can be irreversibly changed from an original state to a new state, but only one time. Thus typically the initial state of the bit position is designated as a “one” or a “zero” and the “zero” can be overwritten with a “one” when data is written onto the medium. Once the data has been written in a section of the medium, which may be all of the medium, that section is considered to be “used” and cannot be re-used for recording new data.
This characteristic of WORM media leads to their principal disadvantage: waste. Even though the medium has very high data storage capacity, the data storage cannot be re-used.
Many attempts have been made in the art to enable the high storage capacity of WORM disk memories to be utilized efficiently in a computer system in a manner analogous to magnetic disk storage systems, wherein data in a given sector can be updated at will. All such attempts, however, have involved some “mapping” of either the physical addresses on the medium that are written to, or of the data already present on the medium. No known method in the art exists of transparently writing new data bits to an already-written WORM medium without mapping.
These earlier attempts have inherent problems. One key problem is how the directory or index of stored data is maintained. Without such directory information, it is impossible to selectively access and retrieve data on the disk. In one approach, when data is stored on the optical disk its location is maintained in some sort of directory or index stored on a companion magnetic floppy or hard disk. This method is obviously inefficient and susceptible to loss of the directory on the magnetic medium, making all data on the optical medium inaccessible.
Another approach has been to combine the above approach with rewriting the entire magnetic memory version of the directory onto the optical disk immediately prior to the removal of the disk or powering down of the system. The disadvantage of this approach is that it uses much disk space since the entire directory may be written onto the disk many times, and it is vulnerable to loss of the directory by power interruption before the directory has been rewritten onto the optical disk.
A third approach relies on address pointer fields associated with each data segment written onto the disk. When data is written onto a particular segment of the optical disk, the associated pointer field remains blank. When an update of the data is desired, it is written to a different segment and the physical address, i.e., the actual physical location on the disk where the updated data has been written, is written to the pointer field of the original data segment. This approach has the inherent disadvantage of long chains of pointers when data is written to the disk many times, and of wasted physical disk space caused by the pointer chains.
Another approach, exemplified by U.S. Pat. No. 4,691,299, is to “map” data bits onto the physical optical disk by using a greater number of physical media bits to represent the data bits. This approach gives the appearance of being able to “rewrite” the optical disk, but in fact the actual data bits on the optical disk are not re-written. Instead, new data bits are used. Like all mapping approaches, this method has the inherent disadvantage of not fully utilizing the physical disk capacity. For example, a mapping scheme that employs four physical media data bits to write three incoming data bits can increase the apparent physical storage capacity of the optical disk by only one-third. More complex mapping schemes may result in higher disk utilization, but never 100% utilization, and at the inherent cost of processing power and delay. This method also allows the physical disk to be re-written only once.
There is thus a need for an apparatus and method for physically erasing and re-writing all physical data bits of a “non-erasable” optical storage medium any number of times, without any mapping of the incoming data to existing data on the disk.
In particular, the 130 mm optical disk products available in the market fit into three categories: magneto-optic, which are writable, erasable, and re-writable; CCW WORM, which is a write-once version of magneto-optic; and ablative (or permanent) WORM, which physically alters the recording layer of the disk when writing data to the disk. These categories are further defined in International Draft Standard ISO/TEC FCD 15286:1997 (E), which specifies the following Type designations:
Type R/W: provides for data to be written, read and erased many times over the recording surface of the corresponding disk side, using the thermo-magnetic and magneto-optical effects.
Type P_ROM: provides for a part of the disk surface to be pre-recorded and reproduced by stamping or other means. This part of the disk is read without recourse to the magneto-optical effect. All parts which are not pre-recorded provide for data to meet the requirements of Type R/W.
Type O-ROM: provides for the whole of the disk surface to be pre-recorded and reproduced by stamping or other means. The corresponding disk sides are read without recourse to the magneto-optical effect.
Type DOW: provides for data to be written and read many times over the recording surface of the corresponding disk side, using the direct overwrite thermo-magnetic and magneto-optical effects requiring a single external magnetic field.
Type P-DOW: provides for a part of the disk surface to be pre-recorded and reproduced by stamping or other means. This part of the disk is read without recourse to the magneto-optical effect. All parts which are not pre-recorded provide for data to meet the requirements of Type DOW.
Type WO: provides write once, read multiple functionality using the thermomagnetic and magneto-optical effects.
Type WO_DOW: provides write once, read multiple functionality using the direct overwrite thermo-magnetic and magneto-optical effects.
The need for a new category is beginning to take shape in the marketplace: one with the technical characteristics of WORM (i.e., Types WO and WO_DOW), but with the ability to selectively delete files completely from the disk in a manner such that the data cannot later be recovered by any means. The primary application for this new product type is where data files, such as tax records, are required to be kept for a prescribed period of time, typically 7 years, but after that time period has expired it is in the best interest of the user to delete this data.
Traditional “erasable” optical disk products do not fully meet this need, because of the chance that data may inadvertently be over-written. Traditional WORM products do not meet this need because the data cannot physically overwritten.
The present invention satisfies this need by providing a method and apparatus such that data on an optical disk cannot be inadvertently overwritten, while at the same time providing the capability to erase completely a given data file or the entire disk surface. Additionally, new data may be written to the erased portions, taking advantage of the entire disk capacity.
SUMMARY OF THE INVENTION
A method for selectively enabling writing of data multiple times onto a write-once read-many optical disk by a host system, the disk having a disk type indicator, and e
Macleod Kent
Vining Richard C.
Hindi Nabil
Plasmon IDE, Inc.
Rider Bennett Egan & Arundel
LandOfFree
Erasable WORM optical disk and method of writing thereto... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Erasable WORM optical disk and method of writing thereto..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Erasable WORM optical disk and method of writing thereto... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2896328