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Browse Prior Art Database

Tape Defect Bypass Mechanism

IP.com Disclosure Number: IPCOM000084318D
Original Publication Date: 1975-Oct-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Ouchi, NK: AUTHOR

Abstract

U. S. Patent 3,765,005, to M. R. Cannon, issued October 9, 1973, and assigned to IBM, describes a tape recording system in which blocks of data are rewritten as a result of a read check. Special indicia are recorded on the tape to indicate that a rewrite had taken place. The indicia may be a special data pattern or signal component. This rewrite procedure has the disadvantage that the indicia are subject to the same error disturbances as the data. Loss of an indicator or a false indication can then result in lost data.

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Tape Defect Bypass Mechanism

U. S. Patent 3,765,005, to M. R. Cannon, issued October 9, 1973, and assigned to IBM, describes a tape recording system in which blocks of data are rewritten as a result of a read check. Special indicia are recorded on the tape to indicate that a rewrite had taken place. The indicia may be a special data pattern or signal component. This rewrite procedure has the disadvantage that the indicia are subject to the same error disturbances as the data. Loss of an indicator or a false indication can then result in lost data.

In the present system, the data stream is segmented into fixed-length blocks, each with its own independent error correction codes. The data blocks are buffered during the readback check to allow a rewrite in the next sequential block space. Blocks are separated so that a read check is completed before the next block must be written. Appended to each block is a logical sequence identifier that is not part of the user written data and is used for control information.

When rewriting occurs, due to a read check, a duplicate block is written following the original block. The duplicated block contains the same identifier as the original block. The identifiers are protected by the error correction codes used for data and, hence, are relatively safe. Since the sequence of identifiers is known when reading, missing or spurious blocks are immediately detected.

With this system, rewritten blocks provide additional opportunity for...