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Twined Interleaving of Data on a Multitrack Storage Medium

IP.com Disclosure Number: IPCOM000084882D
Original Publication Date: 1976-Jan-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 3 page(s) / 50K

Publishing Venue

IBM

Related People

Patel, AM: AUTHOR

Abstract

The twining arrangement of this method provides protection against (1) long errors causing `dead' tracks, (2) length-limited multiple track errors covering all tracks, and (3) many combinations of multiple random errors.

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Twined Interleaving of Data on a Multitrack Storage Medium

The twining arrangement of this method provides protection against (1) long errors causing `dead' tracks, (2) length-limited multiple track errors covering all tracks, and (3) many combinations of multiple random errors.

The arrangement is spontaneously adaptive to the error mode, i.e., the correction capability of the code can be utilized to correct one or the other kind of errors or some partial combination of them, whichever error mode is prominent at a given time or position on the tape. Furthermore, the choice of the amount of interleaving and the amount of twining pitch provide flexibility for adjusting to the error modes at a later time in product plans, without creating major changes in hardware design. This flexibility is very useful when the exact parameters of the error modes may vary or become known only at a later date, when there is no time left for redesign of the hardware.

Consider the 36-track arrangement as shown in the figure. A segment of data consisty of seven sections of data and two check sections. These check sections are computed to form an error correction code (ECC) which provides correction of erasures of up to two sections of the segment. Thirty-six distinct segments (interleaved code words) are arranged in thirty-six tracks in a twined manner.

The first section of the ith segment is placed in the ith track, all such first sections run parallel along the tracks. The second section of ith segment is placed in (i + p)th track, where p is the twining pitch. The third section of ith segment is placed in the (i + 2p)th track and so on; the jth section of ith segment is placed in the [i + (j1)p]th track, computing track number modulo 36. In the example of the figure, p is 4, 1 i 36 and 1 j 9. Note the following properties of the arrangement. (1) This twined arrangement forms a frame of 9 sections x 36 tracks. This determines the buffer requirement in processing for error correction.
(2) Across the tape, no two parallel sections belong to the same segment. Thus, ...