Dynamic magnetic information storage or retrieval – General recording or reproducing – Specifics of equalizing
Reexamination Certificate
1997-09-23
2001-03-06
Kim, W. Chris (Department: 2753)
Dynamic magnetic information storage or retrieval
General recording or reproducing
Specifics of equalizing
C360S046000, C360S048000, C360S073040, C360S073120, C375S232000
Reexamination Certificate
active
06198588
ABSTRACT:
TECHNICAL FIELD
This invention relates to methods and apparatus for data storage, and particularly, though not exclusively, to methods and apparatus for controlling reading of data from elongate magnetic tape media in a helical scan tape drive.
BACKGROUND ART
It is already known to provide reliable storage and retrieval of large volumes of digital data, such as computer data, in particular by means of the DDS (Digital Data Storage) format defined in ISO/IEC Standard 10777:1991 E and implemented in helical scan tape drives made by several companies.
In the DDS system an elongate recording medium comprising tape coated with a magnetic medium is moved by a motor-driven capstan along a path wrapped partially around a transducer comprising a rotating drum carrying one or more electromagnetic heads. The plane of rotation of the drum is disposed at an angle to the plane of movement of the tape, so that each head traverses the tape along successive tracks extending across the width of the tape at an angle to its centreline.
In helical scan data storage devices, it is sometimes necessary or advantageous to employ adaptive filtering in the processing of the signal(s) read from the read head(s). An adaptive filter automatically adjusts its response according to certain properties of the incoming signal. Adaptive filters are well-known and an example of an adaptive filter used in a backup storage device can be seen in Applicants' U.S. Pat. No. 5150379. A typical characteristic of such a filter is a tendency to adopt an undesirable response when presented with a signal which has a spectral content which differs from the normal data signal. In helical scan recording, it is common for such signals to be recorded in margin or preamble parts of the track format.
Typically the precise location of each track is determined during recording of data on the tape by the position relative to the tape of write heads on the drum. To ensure optimum retrieval of data from the tape, it is desirable for read heads on the drum to follow paths across the tape which are at essentially identical positions to those followed by the write heads during data recording. This in turn requires control during data retrieval of relative motion between the tape and the drum, by controlling rotation of the drum and/or controlling movement of the tape by the capstan.
A system for providing such control is described in Applicants' co-pending published European Application No. 671735 and is incorporated herein by reference. In that system, the rotary head drum generates a position signal at one or more predetermined angular positions which is used to control the motion of the media.
This drum position signal is also used as a reference for the generation of a timing signal to enable and inhibit adaption of the filter characteristics according to the position of the read head in the track.
However, it is typical for the height of the recorded tracks relative to the reference edge of the medium to vary according to environmental factors, and across a population of data storage devices. It is therefore necessary to incorporate considerable timing margin in the signal which enables and inhibits filter adaption, so as to guarantee that adaption does not take place at a time when the signal from the read head has undesirable spectral characteristics. As a result, adaption of the filter characteristics is normally enabled relatively late, to the detriment of error performance achieved on the early part of the data.
The present invention aims to overcome this limitation.
DISCLOSURE OF THE INVENTION
According to the present invention there is provided apparatus for reading and writing data to a storage medium, wherein the data is written to the medium in tracks, each track having a predetermined trigger signal pattern, the apparatus comprising:
means for detecting the predetermined trigger signal pattern;
an adaptive filter for signals read from the medium;
and means for triggering adaptive filtering for a track of data on detection of the predetermined trigger signal pattern in that track.
In this way, during a read operation adaptive filtering is triggered on commencement of data with spectral characteristics suitable for adaption of the filter.
In the embodiment to be described, each track comprises data fragments each having a header containing, ancillary information wherein at least a header in an initial data fragment in the track comprises the predetermined trigger signal pattern. Preferably, at least the header of the first data fragment in the track comprises the predetermined trigger signal pattern.
In the embodiment to be described, the predetermined trigger signal pattern is also used to control the motion of the medium.
According to another aspect of the present invention we provide a method of triggering adaptive filtering in apparatus for reading and writing data to a storage medium in the form of tracks comprising:
monitoring for the presence of a predetermined trigger signal pattern during reading of data from a track and triggering adaptive filtering of the data in the track when the the predetermined trigger signal pattern is detected.
REFERENCES:
patent: 5150379 (1992-09-01), Baugh et al.
patent: 5623474 (1997-04-01), Oshio et al.
patent: 0527579A1 (1992-07-01), None
patent: 0577901A1 (1992-07-01), None
patent: 96306933 (1996-07-01), None
Kim W. Chris
Neal Regina Y.
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