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Pseudo Random Recording Channel

IP.com Disclosure Number: IPCOM000084531D
Original Publication Date: 1975-Nov-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 27K

Publishing Venue

IBM

Related People

Hodges, P: AUTHOR [+2]

Abstract

Errors in data read back from magnetic storage media may be caused by the occurrence of worst-case bit patterns or by the presence of similar data on adjacent tracks. Also, feedthrough of the write signal to the track following servo system of a disk file can, for worst-case patterns, cause significant position errors.

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Pseudo Random Recording Channel

Errors in data read back from magnetic storage media may be caused by the occurrence of worst-case bit patterns or by the presence of similar data on adjacent tracks. Also, feedthrough of the write signal to the track following servo system of a disk file can, for worst-case patterns, cause significant position errors.

The incidence of such errors may be reduced by employing the illustrated circuit as a pseudo-random encoder to randomize recorded data, and as a complementary decoder to reconstruct read back data. The circuit consists of a series of one-bit delays D, arranged as a shift register. Between certain of the stages D are exclusive OR gates, such as 4', which receive one input from the preceding stage and a second from the upper line L.

To encode, schematic switch S is in its S2 position and input data is applied at B. The track address or other unique identifier is also applied at input C. A stream of pseudo-random encoded data appears at output D to the recording channel. By including the track address in the randomizing process, identical input data for adjacent tracks is recorded as different randomized bit patterns.

To decode, switch S is in its S1 position and input B is not used. Read back pseudo-random data applied at A produces the original data at D. The initial state of stages D must be identical for both encoding and decoding operations.

In an alternative system, inputs A and B are not used and S is permanently...