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Error Correction by Alternating Read Threshold Levels

IP.com Disclosure Number: IPCOM000092161D
Original Publication Date: 1968-Oct-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 22K

Publishing Venue

IBM

Related People

Irwin, JW: AUTHOR

Abstract

An apparent error resulting from loss of detected signals from a magnetic recording medium, such as magnetic tape, is corrected by alternating the threshold level of the sensor circuits during reread attempts. The threshold level for envelope detectors associated with a magnetic tape is normally higher during a read operation than during write checking. Therefore, two or more tracks dropping below the read threshold level produce an apparently uncorrectable error even though the record write checks correctly.

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Error Correction by Alternating Read Threshold Levels

An apparent error resulting from loss of detected signals from a magnetic recording medium, such as magnetic tape, is corrected by alternating the threshold level of the sensor circuits during reread attempts. The threshold level for envelope detectors associated with a magnetic tape is normally higher during a read operation than during write checking. Therefore, two or more tracks dropping below the read threshold level produce an apparently uncorrectable error even though the record write checks correctly.

The detection of an apparent error causes a signal to be introduced at 11 to partially condition And 10. The tape drive automatically backspaces, or forward spaces if in a read-backward mode, in an effort to reread the record. When this occurs, a signal is produced at 12 which completes the conditioning of 10 and thus sets trigger 15. The threshold level control 16 responds to the output of 15 to produce a signal at output terminal 18 so as to change a DC reference potential being supplied to the energy magnitude sensors, thus reducing the threshold sensitivity level of these sensors. The drive then attempts to reread the record with this lower sensitivity level. If the number of tracks in error is reduced to one, conventional circuitry then corrects for the erroneous track.

If the apparent error persists, a second retry is initiated and a second pulse is introduced at 12, thus resetting 15 and returning...