公开(公告)号：DE2510445A1

公开(公告)日：1975-10-02

申请号：DE2510445

申请日：1975-03-11

Applicant: IBM

Inventor： MARSHALL JOHN WILLIAM ,  MCDONALD JUN EARL GEORGE ,  ROATH PHILLIP BRUCE

IPC: H04L1/00 ,  G11B5/09 ,  G11B20/14 ,  H03K5/1536 ,  H03M5/14 ,  H04L25/08 ,  H04L25/49 ,  G11B5/02

Abstract: Signals read back from a magnetic record medium have assigned sets of legal wavelengths, i.e., elapsed times between any successive two transitions. During readback, the zero crossover, hence the transition location, can be unintentionally phase shifted (as by base line changes) by the channel. The signal is detected and converted to a string of 1's and 0's, wherein the 1's represent detected transitions. A set of three such wavelengths is analyzed for illegal code values representing illegal wavelengths. The illegal code value is then converted to a legal code in accordance with the two adjacent code values in such set. In one embodiment, the illegal code value represented a wavelength that was too short. One of the transitions defining the illegal wavelength is shifted in time toward the longer of two other wavelengths immediately abutting the short illegal wavelength.

公开(公告)号：DE2364788A1

公开(公告)日：1974-06-27

申请号：DE2364788

申请日：1973-12-27

Applicant: IBM

Inventor： MCDONALD JUN EARL GEORGE ,  PATEL ARVIND MOTIBHAI

IPC: G06F12/16 ,  G06F11/10 ,  G11B20/18 ,  H03M13/00 ,  G11B5/02 ,  H03K13/32

Abstract: Error detection is enhanced by using multiple independent error codes combined with nonlinear changes in the data field as applied to different error codes. Such nonlinear permutations increase the probability of detecting errors thereby maximizing the utilization of check bit redundancies. In a magnetic tape subsystem, error detection and correction can be enhanced by scrambling track-to-error code relationships between a plurality of independent codes. Tracks with the highest probability of errors, i.e., the outside tracks on a 1/2 inch tape, for example, are connected to nonadjacent inputs of error correction code apparatus. Additionally, the input-to-track relationship of various code apparatus can be scrambled, either permanently or during a tape transducing operation. The above permutations provide best advantage with selected error correction codes and systems having identifiable probability of error patterns.