Exabyte Corporation

Christopher P Zook

Steven P Georgis

Timothy C Hughes

Christopher Pisciotta

Steve E Haughland

Alireza Atai-Azimi

Robert Bordasch

Harry C Hinz

A dual channel helical scan recording system (30) includes a rotating dum (36) having sets of heads (W1, W2) (R1, R2) mounted on its peripheral surface (56). A set of write heads (W1, W2) is situated on an opposite side of the drum (36) from a set of read heads (R1, R2). The write heads (W1, W2) simultaneously write two adjaent tracks (T1, T2), which are read for verification 180 detrees later by corresponding read heads (R1, R2). The heads (W1, W2, R1, R2) are strategically mounted on the drum (36) with respect to angular and axial placement, and have selected head widths and azimuthal angles. Should a block of data (317) written to tape (32) be determined, during readback, to be bad block, that bad block is subsequently rewritten on the tape (32) in the course of writing good blocks and amongst other good blocks. The rewritten block is recorded at a row position on the tape which is sufficiently displaced from the row position of a previous writing to avoid media defects occuring on the tape. In addition, a block written by a first write head (W1) and perceived as having been written as a bad block must be written by a second write head (W2) before that block is rewritten a predetermined number of times.

Dual channel helical recorder

In a method of encoding and decoding informational data for transmission to a storage medium, a group G of physical blocks written to the storage medium includes both user data information blocks and auxiliary error correction blocks. Each block (B.sub.r,c) included in the group G belongs both to a row r and a column c. Informational data is formatted into preselected bit positions of the user data information blocks. Values for bit positions in the auxiliary error correction blocks are generated by performing an exclusive OR operation upon values in corresponding bit positions in a subgroup of strategically selected user data blocks. By strategically selecting the user data blocks to be included in the subgroup, the method facilitates recovery of entire blocks, and even rows or columns of blocks.

Error correction method and apparatus

For decoding a Reed-Solomon codeword with (n-K) check characters an error/erasure locator (32) executes a codeword cycle comprising (n-K) 'coefficient' iterations followed by (n-K) 'modified syndrome' iterations. The error/erasure locator (32) includes a bank (52) of simultaneously loadable syndrome registers and a bank (56) of coefficient registers. The syndrome registers are connected to one another in a circular shift path (91). The error/erasure locator (32) further includes a cascading arrangement of PISO multipliers (54), a SIPO multiplier (60), and PISO multipliers (61). The PISO multipliers (54) operate upon the contents of the syndrome registers (52) (expressed in a conventional basis representation) and the contents of the coefficient register (56) (expressed in dual basis representation) to obtain a serial current discrepancy d.sub.n. The SIPO multiplier 60 multiplies the serial current discrepancy d.sub.n by a parallel-formatted multiplicative inverse d.sub.m.sup.-1 .beta..sub.i of a prior discrepancy (expressed in dual basis representation) to obtain in one set of clock cycles, the product d.sub.n d.sub.m.sup.-1. During a second set of clock cycles the discrepancy product d.sub.n d.sub.m.sup.-1 is further multiplied using a second bank (61) of PISO multipliers by the contents of corresponding auxiliary registers (62) to obtain a serial product useful for updating the coefficient registers (56). The syndrome registers (52) perform the dual purpose of storing the original syndromes during the coefficient iteration and of storing the modified syndromes produced during the modified syndrome iteration.

Method and apparatus for determining the coefficients of a locator

An error correction system (20) comprises a multi-pass controller (32) which operates through a controller/decoder interface (34) to supervise the execution of decoding passes by a decoder (30). The multi-pass controller (32) employs a correction procedure comprising a plurality of hierarchial strategies S(1), S(2), . . . S(N) for transitioning the procedure through a plurality of predetermined states. Upon completion of a decoding pass, a pass evaluator (70) evaluates the results of the decoding pass and uses the evaluation for establishing values for further operation. Further passes are executed in accordance with further states determined by the multi-pass controller (32), the further states having particular parameters associated therewith including a strategy selection.

Multiple pass error correction process and apparatus for product codes

Apparatus and method are disclosed for formatting and recording digital information. Recording is effected by discrete stripes on 8 mm magnetic tape using a helical scan arrangement that enables a high recording density and a low error rate. Formatting in the data area of each stripe includes recording of digital information within preamble, data block, and postamble sections. The preamble section provides frequency/phase and location referencing, the data block section includes a plurality of physical data blocks each of which are divided into sub-blocks that include synchronizing and identifying information along with data to be recorded, and the postamble section ensures compatibility of physical alignment between the recording heads and magnetic tape.

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Lafayette, CO, United States of America

Christopher P Zook