Plural channel error correcting methods and means using adaptive reallocation of redundant channels among groups of channels

摘要

Where data is recorded on logically independent sets of parallel channels or tracks, the correction of error of very long (infinite) length cannot be advantageously treated by conventional coding methods unlike finite length error such as single shot or burst noise. To ensure the correction of channels in error from data recovered from a multi- channel storage medium, a fixed number of channels per set are dedicated to error checking bits. In this invention, more than the usual number of channels in error in any one set are made correctable by adaptively reallocating the unused redundant channels in the other set. This is accomplished by encoding and recording in the first redundant channel in each set vertical parity checks limited to that set while encoding and recording in the second redundant channel of each set, the parity of data taken over both sets of channels in a predetermined positively or negatively sloped direction. With this type of parity information so recorded, then the data obtained from up to three known erroneous channels in any one set may be corrected, provided that two sets together aggregate not more than four channels in error. Advantageously, the vertical and cross-parity checking information can also be used to generate an internal channel-in-error pointer for the first erroneous track in each set. Additionally, this data can be made to yield a second internal channel-in-error pointer in at least one of the sets. Lastly, error patterns are identified upon decoding at the intersection of at least two error syndromes one of which is derived from cross-parity checking bits.