Abstract: A method for operating a disk drive having timing marks (TMs) on the disk that are chosen to reduce the probability of misidentification of a TM in the presence of read errors. The disk drive searches for TMs within a fixed TM search window which extends past the TM on the disk. A TM preferably maximizes the post-shift sliding distance for m post-shifts of the TM pattern, where m corresponds to the TM search window boundary. In this manner, the probability of a misidentification of the TM due to a post-shift having a small distance from the TM pattern is reduced. The TM pattern also provides pre-shift error resistance.

Abstract: An error correction encoder inserts redundant parity information into a data stream to improve system reliability. The encoder can generate the redundant parity information using a composite code. Dummy bits are inserted into the data stream in locations reserved for parity information generated by subsequent encoding. The error correction code can have a uniform or a non-uniform span. The span corresponds to consecutive channel bits that are within a single block of a smaller parity code that is used to form a composite code. The span lengths can be variant across the whole codeword by inserting dummy bits in less than all of the spans.

Abstract: Techniques are provided for performing substitutions of bit sequences that are known to cause errors. Input data is initially modulation encoded. The modulated data is then analyzed in a sliding window to determine if it contains any additional bit sequences that are known to cause errors. If an error prone bit sequence is identified in the data, a substitution engine replaces the error prone bit sequence with a predetermined pattern of bits that is less likely to cause errors. The bit stream output of the substitution engine is then recorded on a storage medium. The recorded bit stream is decoded when it read from the medium. The decoding process identifies the substituted bit pattern and replaces the substituted pattern with the original sequence of bits.

Abstract: Techniques are provided for applying modulation constraints to data streams divided into separate interleaved portions. The even and odd bits in a data stream are separated into two data paths. A first modulation encoder encodes the even bits according to a first constraint. A second modulation encoder encodes the odd bits according to a second constraint. The two encoded data streams are then interleaved to form one data stream. The modulation encoders can encode the two data paths using Fibonacci encoding.

Abstract: A method, apparatus and program storage device for correcting a burst of errors together with a random error using cyclic or shortened cyclic codes is disclosed. The present invention solves the above-described problems by providing a received word to a syndrome register defined by a polynomial of degree n-k, said polynomial generating a cyclic or shortened cyclic code, wherein n is the length and k is the number of information bits in the codeword. The syndrome gets modified each time the received (possibly noisy) word is shifted. The contents of the syndrome register are processed to identify a random error together with an error burst of the received word. Then correction of the random error and the burst is made and a corrected codeword is generated.

Abstract: A position of a moveable object may be encoded and indicated by a skew-tolerant Gray code on the object. Skew-tolerant Gray codes have the property that consecutive code words differ in only one co-ordinate position, and the additional property that, in each consecutive group of three consecutive code words, the first and third code words differ in only two adjacent coordinate positions.

Abstract: Geometrically-dependent error rates are used to identify sectors for XORing data in a RAID system for parity purposes in such a way that the probability of failure of any particular group is minimized.

Abstract: Provided is a method, system, and program for providing synchronization in a binary data stream. A binary data stream is received. A synchronization mark having at least one isolated peak is generated into at least one point in the data stream. An encoded data stream is formed by concatenating the synchronization mark with the received binary data. During decoding, the synchronization mark is detected based on error propagation occurring adjacent to the at least one isolated peak of the synchronization mark.

Abstract: Techniques are provided for performing substitutions of bit sequences that are known to cause errors. Input data is initially modulation encoded. The modulated data is then analyzed in a sliding window to determine if it contains any additional bit sequences that are known to cause errors. If an error prone bit sequence is identified in the data, a substitution engine replaces the error prone bit sequence with a predetermined pattern of bits that is less likely to cause errors. The bit stream output of the substitution engine is then recorded on a storage medium. The recorded bit stream is decoded when it read from the medium. The decoding process identifies the substituted bit pattern and replaces the substituted pattern with the original sequence of bits.

Abstract: Techniques are provided for applying modulation constraints to data streams divided into separate interleaved portions. The even and odd bits in a data stream are separated into two data paths. A first modulation encoder encodes the even bits according to a first constraint. A second modulation encoder encodes the odd bits according to a second constraint. The two encoded data streams are then interleaved to form one data stream. The modulation encoders can encode the two data paths using Fibonacci encoding.

Abstract: Non-uniform modulation encoding techniques are provided to prevent data from containing bit patterns that are prone to errors during read back. Modulation encoding is performed on a data stream to remove error prone bit patterns. Unconstrained data, such as error check parity, that is inserted into the modulated data stream may contain error prone bit patterns. Stricter modulation constraints are enforced on bits that are next to the unconstrained data, than on the remaining bits. By enforcing stricter modulation constraints on these bits, an entire data bit stream can have a desired modulation constraint.

Abstract: Techniques are provided for applying modulation constraints to data streams using a short block encoder. A short block encoder encodes a subset of the bits in a data stream. Then, the even and odd interleaves in a data stream are separated into two data paths. A first modulation encoder encodes the even interleave according to a first modulation constraint. A second modulation encoder encodes the odd interleave according to a second modulation constraint, which in general coincides with the modulation constraint for even interleave.

Abstract: A disk drive has timing marks (TMs) on the disk, that are chosen to reduce the probability of misidentification of a TM in the presence of read errors. The disk drive searches for TMs within a fixed TM search window which extends past the TM on the disk. A TM preferably maximizes the post-shift sliding distance for m post-shifts of the TM pattern, where m corresponds to the TM search window boundary. In this manner, the probability of a misidentification of the TM due to a post-shift having a small distance from the TM pattern is reduced. The TM pattern also provides pre-shift error resistance.

Abstract: A method (and system) of finding byte synchronization over random data, which includes selecting a synchronization symbol maximizing the Hamming distance when slid over itself, and appending the synchronization symbol to random data.

Abstract: Skew-tolerant Gray codes have the property that consecutive code words differ in only one co-ordinate position, and the additional property that, in each consecutive group of three consecutive code words, the first and third code words differ in only two adjacent coordinate positions.

Abstract: Provided is a method, system, and program for storing input groups of uncoded binary data on a storage medium. A plurality of uncoded data blocks in a data stream are received. An encoded data stream is obtained from concatenating successive encoded blocks such that the encoded data stream includes a predetermined bit pattern comprising a plurality of bits. The bit pattern always occurs within a first number of bits and two occurrences of a “1” or “0” occur within a second number of bits. The encoded data blocks are stored on the storage medium.

Abstract: Bit and byte synchronization for sampling and decoding a data string is provided a single data field u. The data string x has pre-pended to it a short string of is (ones), followed by u to yield a string y= . . . 1111, u, x. The string is pre-coded by convolution with 1/(1?D2). PRML-sampling of y starts at an initial phase, and vectors are obtained from that string by sampling at pre-selected phases following the initial sampling point. The vectors of y are compared with vectors corresponding to PRML samples of an initial set of bits in u obtained at predetermined phases. The pair of y, u vectors exhibiting the minimum Euclidian distance yields a sampling correction value by which the initial sampling phase is corrected and a new initial sampling point preceding x is determined. Here, bit and byte synchronization have been achieved and sampling of x proceeds at the corrected phase, from the new initial sampling point.

Abstract: Skew-tolerant Gray codes have the property that consecutive code words differ in only one co-ordinate position, and the additional property that, in each consecutive group of three consecutive code words, the first and third code words differ in only two adjacent coordinate positions.

Abstract: A method, apparatus and program storage device for correcting a burst of errors together with a random error using cyclic or shortened cyclic codes is disclosed. The present invention solves the above-described problems by providing a received word to a syndrome register defined by a polynomial of degree n-k, said polynomial generating a cyclic or shortened cyclic code, wherein n is the length and k is the number of information bits in the codeword. The syndrome gets modified each time the received (possibly noisy) word is shifted. The contents of the syndrome register are processed to identify a random error together with an error burst of the received word. Then correction of the random error and the burst is made and a corrected codeword is generated.

Abstract: A position of a moveable object may be encoded and indicated by a skew-tolerant Gray code on the object. Skew-tolerant Gray codes have the property that consecutive code words differ in only one co-ordinate position, and the additional property that, in each consecutive group of three consecutive code words, the first and third code words differ in only two adjacent coordinate positions.