Dynamic magnetic information storage or retrieval – General recording or reproducing – Recording-or erasing-prevention
Reexamination Certificate
2002-03-18
2004-07-20
Faber, Alan (Department: 2651)
Dynamic magnetic information storage or retrieval
General recording or reproducing
Recording-or erasing-prevention
C386S349000, C380S203000, C369S053210
Reexamination Certificate
active
06765739
ABSTRACT:
BACKGROUND
The present invention relates to recording and transmission of digital data, and more particularly, to methods of recording machine-readable media to inhibit unauthorized copying.
Digital information is often recorded on various machine-readable media such as optical discs for mass distribution. For example, computer software and audio files (such as music on compact disc (CD)), and video files (such as movies on digital video disc (DVD)) are commonly distributed on physical discs. Compact discs and DVD's are subject to formatting standards for digitally recorded data, software, images, and audio. Herein after, the phrases “digital information” or “digital data” are intended to include, without limitations, software, audio, video, and other digitized information. Further, the word “disc” includes, without limitation, optical and magnetic data storage disc devices (such as CD's and DVD's) and the phrase “machine-readable media” includes without limitation magnetic tapes, solid state memory, and similar machine-readable data storage devices.
Stamped discs, such as CD's and DVD discs, typically store information as a spiral track of embossed pits, or embossed marks. For example, a mark represents one of two binary digits, say a “1,” and the unmarked area, or “space,” represents the other binary digit, say a “0.” The depth of these embossed marks is typically equal to or less than one quarter the wavelength of light used for reading the disc. This depth is carefully selected to provide near-maximum variation in intensity between reading of embossed marks and reading of spaces between the embossed marks while also providing a reliable tracking error signal. This design allows for near-maximal signal to noise ratio during the read operation.
Such discs do not contain the digital data in its original form. In fact, digital data are rarely recorded in its original digital form. Instead, high capacity digital recording typically involves numerous tradeoffs of various constraints and requirements, resulting in the original digital data being encoded into bit patterns that satisfy these constraints. A first constraint deals with a tradeoff between recording density and error rate. The need for a sufficiently small error rate imposes a requirement for additional information such as error correction code (ECC) to be added to the digital data for error detection and correction.
A second constraint deals with the highest permissible transition frequency, where a transition is a change from one media state such as an embossed mark to another media state such as an unmarked area. In magnetic data recording, a related limitation is commonly called intersymbol interference. Typically, in reading a recording medium such as a magnetic or optical recording medium, the signal produced by each transition of state has a distorting effect on the signal produced by neighboring transitions. This distortion imposes a maximum on the number of consecutive transitions that can be reliably read at a specified minimum transition spacing. In any recording medium, there is also a maximum allowable spatial frequency at which some physical phenomenon can switch states during recording or stamping. In magnetic recording media, the physical phenomenon is the direction of magnetic alignment of metallic particles. In optical stamped media, the physical phenomenon is the height difference between the unmarked surface and the pits (or bumps) of the medium. In recordable optical phase change media, the physical phenomenon is the crystaline phase of the recording medium, the two crystalline phases having different refractive indices.
A third typical constraint is self-clocking. For serial binary data, a clock signal for decoding the data often must be extracted from the timing of the transitions of a read signal (reversal of voltage or current, change of frequency or phase, change of light intensity, etc.). There must be an adequate frequency of transitions to keep the clock signal synchronized. Serial binary data are often physically in a format called Non Return to Zero Inverted (NRZI). In NRZI format, the waveform is at one state until a binary one occurs, at which time the waveform switches to an opposite state. The maximum transition rate, or intersymbol interference limitations discussed above, imposes a minimum on the amount of time that can pass between transitions. The requirement for self clocking imposes a maximum on the amount of time that can pass with no transition. A code that satisfies the maximum transition rate constraint, the self-clocking constraint, and the NRZI format requirements is commonly called a Run Length Limited (RLL) code. In a RLL code, the number of consecutive binary zeros in the encoded bit pattern must be at least as large as a specified non-zero minimum and no greater than a specified maximum. For example, compact discs typically use a code specified as (2,10)-RLL which means that the number of consecutive zeros in the encoded bit pattern must be at least 2 and no greater than 10.
A fourth typical constraint on the encoded binary signal is a requirement for a limit on the low frequency content of the read signal. In many read channel detection systems (for example, a differential phase detection system), a transition is indicated when the read signal crosses a fixed threshold (the threshold between a mark and a space). Any low frequency content in the read signal can cause an offset, restricting the dynamic range of the detection system. In addition track following and focusing signals (collectively referred to as “tracking” signals) are often implemented using the low frequency modulation content of the read signal. Any low frequency content in the read signal due to data patterns may interfere with tracking.
Again in the NRZI format, one state of a signal (for example, the pit, or the mark) is assigned the value +1 and the opposite state (for example, the space) is assigned the value −1. A sum of these values is called Digital Sum Variance (DSV) or alternatively Running Digital Sum (RDS). For many detectors, there is a specified maximum DSV or RDS, and any DSV exceeding the specified maximum is likely to cause data read errors, servo problems, or loss of tracking.
In
FIG. 1
, the process
20
of creating an original disc
14
from original data
12
is illustrated. First, the original data
12
are read as illustrated by step
22
. Then, error correction code (ECC) is added to the data. Step
24
. The ECC is added to correct errors due to manufacturing defects and reading errors. This is well known in the art.
Next, the data, including the ECC, are encoded to channels bits. Step
26
. The encoding step produces a sequence of bits that, collectively, meet the second, the third, and the fourth constraints discussed herein above. Finally, the channel bits, representing the encoded data plus the ECC, are written on an original disc
14
. Step
28
. In this document, the words “write” and “writing” of a disc includes, without limitation, various technologies and creation techniques to produce, for example, an optical CD or a DVD including stamping, burning, and fabricating.
The process
30
of duplicating the original disc
14
to a duplicate disc
18
is also illustrated in FIG.
1
. To copy the original disc
14
, first, the above-described steps are applied in a reverse order to retrieve the data illustrated as recovered data
16
in FIG.
1
. Then, the above-described steps are repeated, using the recovered data
16
as input, to write a duplicate disc
18
.
In more particular, to produce the duplicate disc
18
, the original disc
14
is read to retrieve the channel bits. Step
32
. Then, the channel bits are decoded to the underlying data plus the ECC. Step
34
. Next, the ECC is removed from the decoded data to recover the original data. Step
36
. The recovered data
16
need not be saved; however, the recovered data
16
are typically saved, at minimum, on a machine-readable memory such as on random access memory (RAM). Step
38
. At th
Hogan Josh N.
Towner David K.
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