US4914535A — Synchronization for stored data

Claim 1

Independent Claim 135 words

A method of identifying the location of a sequence of data bits stored on a storage medium, comprising generating a predetermined synchronization sequence of symbols, each said symbol comprising a plurality of bits, storing on said storage medium a bit sequence corresponding to said predetermined synchronization sequence to indicate said location of said data bit sequence, deriving from said stored corresponding bit sequence on said storage medium a trial sequence of symbols, each said symbol comprising a plurality of bits, and determining whether said trial sequence corresponds to said predetermined synchronization sequence by comparing said trial sequence with said predetermined synchronization sequence symbol by symbol and, based on said comparing, determining the number of symbols in which said trial sequence differs from said predetermined synchronization sequence, whereby the effect of clustered bit errors is reduced.

Claim 2

Independent Claim 135 words

A method of identifying the location of a sequence of data bits stored on a storage medium, comprising generating a predetermined synchronization sequence of symbols, each said symbol comprising a plurality of bits, storing on said storage medium a bit sequence corresponding to said predetermined synchronization sequence to indicate said location of said data bit sequence, deriving from said stored corresponding bit sequence on said storage medium a trial sequence of symbols, each said symbol comprising a plurality of bits, and determining whether said trial sequence corresponds to said predetermined synchronization sequence by comparing said trial sequence with said predetermined synchronization sequence symbol by symbol and, based on said comparing, determining the number of symbols in which said trial sequence differs from said predetermined synchronization sequence, whereby the effect of clustered bit errors is reduced.

Claim 3

Independent Claim 109 words

A method of identifying the location of a sequence of data bits stored on a storage medium, said stored data bits being encoded from raw data bits in accordance with a code in which raw data bits are encoded as encoded bit groups of at least two different lengths, comprising generating a predetermined synchronization sequence, and storing on said storage medium a bit sequence corresponding to said synchronization sequence to indicate said location of said data bit sequence, said synchronization sequence comprising a sequence of raw data symbols which encode, in accordance with said code, as encoded bit groups all of a single length, whereby error propagation is reduced.

Claim 4

Independent Claim 109 words

A method of identifying the location of a sequence of data bits stored on a storage medium, said stored data bits being encoded from raw data bits in accordance with a code in which raw data bits are encoded as encoded bit groups of at least two different lengths, comprising generating a predetermined synchronization sequence, and storing on said storage medium a bit sequence corresponding to said synchronization sequence to indicate said location of said data bit sequence, said synchronization sequence comprising a sequence of raw data symbols which encode, in accordance with said code, as encoded bit groups all of a single length, whereby error propagation is reduced.

Claim 5

Dependent Claim 86 words

The method of claim 2 further comprising derived from said stored corresponding bit sequence on said storage medium a trial sequence of symbols, and determining whether said trial sequence corresponds to said predetermined synchronization sequence by comparing said trial sequence with said predetermined synchronization sequence symbol by symbol and, based on said comparing, determining the number of symbols in which said trial sequence differs from said predetermined synchronization sequence, each said symbol comprising a plurality of bits, whereby the effect of clustered bit errors is reduced.

Claim 6

Dependent Claim 47 words

The method of claim 1 or 3 wherein said synchronization sequence comprises at least one zero-valued symbol followed by a predetermined sequence of N symbols, N an integer, and said trial sequence comprises N successive symbols derived from the stored bit sequence corresponding to the synchronization sequence.

Claim 7

Dependent Claim 38 words

The method of claim 1 or 3 wherein said deriving step further comprises deriving a succession of said trial sequences and determining the number of symbols in which each said trial sequence differs from said predetermined synchronization sequence.

Claim 8

Dependent Claim 32 words

The method of claim 1 or 3 further comprising determining if said number of symbols in which said trial sequence differs from said predetermined synchronization sequence is less than a predetermined number.

Claim 9

Dependent Claim 88 words

The method of claim 1 or 2 wherein said predetermined synchronization sequence is chosen so that the number of symbols by which said predetermined synchronization sequence differs from any version of said predetermined sequence that is shifted by one or more bits in a particular direction is no less than a minimum distance D, and wherein said method further comprises determining that said synchronization sequence has been found if said number of symbols by which said trial sequence differs from said predetermined sequence is no greater than (D-1)/2.

Claim 10

Dependent Claim 96 words

The method of claim 1 wherein said data bits stored on said medium are derived from raw data bits in accordance with a code in which groups of said raw data bits are encoded as sets of encoded bits, there are at least two different lengths of said sets such that decoding of possibly erroneous encoded bit sets may produce error propagation, said predetermined synchronization sequence comprises groups of data bits all of one length, and said corresponding bit sequence is encoded from said predetermined synchronization sequence, whereby error propagation in said synchronization sequence is avoided.

Claim 11

Dependent Claim 65 words

The method of claim 1 or 2 wherein groups of raw data bits of two different lengths are mapped into groups of encoded said data bits in accordance with a rate 2/3 variable length modulation code, and said symbols of said predetermined synchronization sequence are all of one said length and are encoded for storage in accordance with said rate 2/3 variable length modulation code.

Claim 12

Dependent Claim 59 words

The method of claim 9 wherein said rate 2/3 code is characterized in that two bit-long groups of raw data bits are mapped into three-bit long groups of encoded data bits, four-bit long groups of raw data bits are encoded into six-bit long groups of encoded data bits, and each symbol of said predetermined synchronization sequence is two-bits long.

Claim 13

Dependent Claim 75 words

The method of claim 10 wherein groups of raw data bits are mapped into groups of encoded data bits according to the following table: ______________________________________ Raw Data Bits Encoded Bits ______________________________________ 00 x00 01 x01 10 010 1100 x00000 1101 x00001 1110 010000 1111 010001 ______________________________________ (where x denotes the complement of the previous encoded bit), and each symbol of said predetermined synchronization sequence is chosen from the set of symbols 00, 01, and 10.

Claim 14

Dependent Claim 79 words

The method of claim 1 or 2 wherein said storage medium comprises a ferro-magnetic rotatable disk, said bit sequences are stored serially along a track of said ferro-magnetic disk, said storing includes representing a bit having a first value by a transition of magnetization polarity and a bit having a second value by an absence of a state transition of magnetization polarity, and said stored bit sequence corresponding to said synchronization sequence immediately precedes said sequence of data bits.

Claim 15

Dependent Claim 13 words

The method of claim 1 wherein each said symbol comprises two said bits.

Claim 16

Dependent Claim 29 words

The method of claim 1 or 2 wherein said symbols are drawn from an alphabet of symbols 0, 1, 2 respectively representing the bit pairs 00, 01, and 10.

Claim 17

Dependent Claim 23 words

The method of claim 14 wherein said predetermined synchronization sequence comprises at least one leading zero symbol followed by the symbol sequence 21110.

Claim 18

Dependent Claim 21 words

The method of claim 14 wherein said synchronization sequence comprises at least one leading zero followed by the symbol sequence 211101.

Claim 19

Dependent Claim 21 words

The method of claim 14 wherein said synchronization sequence comprises at least one leading zero followed by the symbol sequence 2220210.

Claim 20

Dependent Claim 21 words

The method of claim 14 wherein said synchronization sequence comprises at least one leading zero followed by the symbol sequence 222210201.

Claim 21

Dependent Claim 21 words

The method of claim 14 wherein said synchronization sequence comprises at least one leading zero followed by the symbol sequence 2220110210.

Claim 22

Dependent Claim 21 words

The method of claim 14 wherein said synchronization sequence comprises at least one leading zero followed by the symbol sequence 111102210201.

Claim 23

Dependent Claim 21 words

The method of claim 14 wherein said synchronization sequence comprises at least one leading zero followed by the symbol sequence 22211101102101.

Claim 24

Dependent Claim 21 words

The method of claim 14 wherein said synchronization sequence comprises at least one leading zero followed by the symbol sequence 222111010110210.

Claim 25

Dependent Claim 21 words

The method of claim 14 wherein said synchronization sequence comprises at least one leading zero followed by the symbol sequence 22210222021011020.

Claim 26

Dependent Claim 21 words

The method of claim 14 wherein said synchronization sequence comprises at least one leading zero followed by the symbol sequence 222211022202021021.

Claim 27

Dependent Claim 21 words

The method of claim 14 wherein said synchronization sequence comprises at least one leading zero followed by the symbol sequence 22111101102110102021.

Claim 28

Dependent Claim 21 words

The method of claim 14 wherein said synchronization sequence comprises at least one leading zero followed by the symbol sequence 222211102110210110101.

Claim 29

Dependent Claim 141 words

Apparatus for identifying the location of a sequence of data bits stored on a storage medium, comprising circuitry for generating a predetermined synchronization sequence of symbols, each said symbol comprising a plurality of bits, circuitry for storing on said storage medium a bit sequence corresponding to said predetermined synchronization sequence to indicate said location of said data bit sequence, circuitry for deriving a trial sequence of symbols from said bit sequence stored on said storage medium, each said symbol comprising a plurality of bits, and circuitry for determining whether said trial sequence corresponds to said predetermined synchronization sequence by comparing said trial sequence with said predetermined synchronization sequence symbol by symbol and, based on said comparing. determining the number of symbols in which said trial sequence differs from said predetermined synchronization sequence, whereby the effect of clustered bit errors is reduced.

Claim 30

Dependent Claim 141 words

Apparatus for identifying the location of a sequence of data bits stored on a storage medium, comprising circuitry for generating a predetermined synchronization sequence of symbols, each said symbol comprising a plurality of bits, circuitry for storing on said storage medium a bit sequence corresponding to said predetermined synchronization sequence to indicate said location of said data bit sequence, circuitry for deriving a trial sequence of symbols from said bit sequence stored on said storage medium, each said symbol comprising a plurality of bits, and circuitry for determining whether said trial sequence corresponds to said predetermined synchronization sequence by comparing said trial sequence with said predetermined synchronization sequence symbol by symbol and, based on said comparing. determining the number of symbols in which said trial sequence differs from said predetermined synchronization sequence, whereby the effect of clustered bit errors is reduced.

Claim 31

Dependent Claim 114 words

Apparatus for identifying the location of a sequence of data bits stored on a storage medium, said stored data bits being encoded from raw data bits in accordance with a code in which raw data bit symbols are encoded as data bit groups of at least two different lengths, comprising circuitry for generating a predetermined synchronization bit sequence, circuitry for storing on said storage medium a bit sequence corresponding to said synchronization sequence to indicate said location of said data bit sequence, said synchronization sequence comprising a sequence of raw data symbols which encode, in accordance with said code, as stored encoded bit groups all of a single length, whereby error propagation is reduced.

Claim 32

Dependent Claim 114 words

Apparatus for identifying the location of a sequence of data bits stored on a storage medium, said stored data bits being encoded from raw data bits in accordance with a code in which raw data bit symbols are encoded as data bit groups of at least two different lengths, comprising circuitry for generating a predetermined synchronization bit sequence, circuitry for storing on said storage medium a bit sequence corresponding to said synchronization sequence to indicate said location of said data bit sequence, said synchronization sequence comprising a sequence of raw data symbols which encode, in accordance with said code, as stored encoded bit groups all of a single length, whereby error propagation is reduced.

Claim 33

Dependent Claim 164 words

Apparatus for synchronizing a read head of a mass storage medium with respect to the beginning of a stored sequence of data bits comprising a synchronization sequence of symbols chosen to maximize the minimum Hamming distance, symbol-by-symbol, of said synchronization sequence and versions of said synchronization sequence that are shifted relative to said synchronization sequence by one or more bits, an encoder for encoding said synchronization sequence in accordance with a code in such a way that all code words into which symbols of said synchronization sequence may be encoded have the same length, circuitry for storing said encoded code words on said medium to indicate the beginning of said stored sequence of data bits, a decoder for reading trial sequences of said stored code words and decoding said trial sequences, and circuitry for determining the Hamming distance, symbol-by-symbol, between each said trial subsequence and said synchronization sequence and for determining said location based on when said Hamming distance falls below a predetermined value.

Claim 34

Dependent Claim 164 words

Apparatus for synchronizing a read head of a mass storage medium with respect to the beginning of a stored sequence of data bits comprising a synchronization sequence of symbols chosen to maximize the minimum Hamming distance, symbol-by-symbol, of said synchronization sequence and versions of said synchronization sequence that are shifted relative to said synchronization sequence by one or more bits, an encoder for encoding said synchronization sequence in accordance with a code in such a way that all code words into which symbols of said synchronization sequence may be encoded have the same length, circuitry for storing said encoded code words on said medium to indicate the beginning of said stored sequence of data bits, a decoder for reading trial sequences of said stored code words and decoding said trial sequences, and circuitry for determining the Hamming distance, symbol-by-symbol, between each said trial subsequence and said synchronization sequence and for determining said location based on when said Hamming distance falls below a predetermined value.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	1993-04-02	1993-10-02	1994-04-03	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	1997-04-02	1997-10-02	1998-04-03	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	2001-04-02	2001-10-02	2002-04-03	$7700.00	Window Closed / Lapsed

Synchronization for stored data

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