Timing based servo system for magnetic tape systems

• US 5,689,384 A
• Filed: 06/30/1994
• Issued: 11/18/1997
• Est. Priority Date: 06/30/1994
• Status: Expired due to Term

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Eaton, James Howard, Albrecht, Thomas Robert, Barrett, Robert Carl
• Primary Examiner(s): Psitos, Aristotelis M.
• Assistant Examiner(s): HABERMEHL, JAMES LEE
• Application Number:
  US08/270,207
• Time in Patent Office: 1,237 Days
• Field of Search: 360/77.05, 360/77.07, 360/77.71, 360/77.12, 360/76
• US Class Current: 360/77.12
• CPC Class Codes: G11B 5/584 for track following on tapes

Abstract

A track following servo system is disclosed for use with magnetic tape systems in which magnetic servo track patterns contain transitions recorded at more than one azimuthal orientation across the width of the servo track. The timing of a signal derived from reading at any point across the width of such a pattern varies continuously as the read head is moved across the servo track. The pattern is read by a servo read head whose width is small compared to the servo track pattern. The combination of a wide servo pattern and a narrow servo read head offers excellent position sensing linearity and dynamic range. In the preferred embodiment, the servo read head is also narrow with respect to the data tracks, which provides the additional advantages of superior immunity to position sensing errors caused by defects or temporal variations in the servo read head, defects in the servo pattern on the tape, wear of the head or tape, or debris collection on the head or tape. Position sensing with this system is achieved by deriving a ratio of two servo pattern intervals and therefore is insensitive to tape speed during reading. The servo patterns may include spacing intervals recognizable for error detection and correction purposes. Servo tracks are recorded using a patterned multiple gap servo write head whose magnetic gaps have geometries appropriate to generate the desired servo patterns. The patterned gaps of the servo write head are produced by photolithographically defined electroplating of permalloy on a ferrite ring head structure.

Claims

1. A servo control system for positioning a magnetic head adjacent a surface of a moving magnetic storage medium for reading a servo pattern recorded in at least one track on the storage medium surface, the system comprising:

a head assembly having at least one servo read head for reading the servo pattern on the storage medium in a transducing direction and generating a read head signal representative of the servo pattern;

a servo decoder that receives the read head signal and decodes it to generate a position signal that indicates the position of the read head relative to the servo pattern;

a translation assembly that is activated to position the head assembly relative to the storage medium; and

a servo controller that activates the translation assembly in accordance with the position signal;

the servo decoder including means for decoding a read head signal produced from a servo pattern that comprises a cyclic sequence of magnetic flux transitions that extend continuously across the width of the track and define servo pattern stripes such that the servo read head signal varies as the magnetic head is moved across the width of the track, the stripes including at least a first azimuthal orientation and a second azimuthal orientation, such that the first azimuthal orientation is not parallel to the second azimuthal orientation, and the servo decoder includes means for determining time intervals between a plurality of predetermined pairs of transitions in the servo pattern and generating a substantially speed invariant position signal that is a function of the time intervals.

2. A servo control system as defined in claim 1, wherein the signal decoder detects signals from the read head corresponding to magnetic flux transitions having a first flux polarity and ignores magnetic flux transitions having a second flux polarity.

3. A servo control system as defined in claim 1, wherein the signal decoder decodes a read head signal produced from a servo pattern in which the stripes are arranged in groups having a plurality of sequential stripes at the first orientation followed by a plurality of sequential stripes at the second orientation and in which the groups are separated by synchronization features.

4. A servo control system for positioning a magnetic head adjacent a surface of a moving magnetic storage medium for reading a servo pattern recorded in at least one track on the storage medium surface, the system comprising:

a head assembly having at least one servo read head for reading the servo pattern on the storage medium in a transducing direction and generating a read head signal representative of the servo pattern;

a servo decoder that receives the read head signal and decodes it to generate a position signal that indicates the position of the read head relative to the servo pattern;

a translation assembly that is activated to position the head assembly relative to the storage medium; and

a servo controller that activates the translation assembly in accordance with the position signal;

the servo decoder including means for decoding a read head signal produced from a servo pattern that comprises a cyclic sequence of magnetic flux transitions that extend continuously across the width of the track and define servo pattern stripes such that the servo read head signal varies as the magnetic head is moved across the width of the track, the stripes including at least a first azimuthal orientation and a second azimuthal orientation, such that the first azimuthal orientation is not parallel to the second azimuthal orientation, and the servo decoder includes means for determining time intervals between a plurality of predetermined pairs of transitions in the servo pattern and generating a substantially speed invariant position signal that is a function of the time intervals;

wherein the servo decoder generates a position signal value in accordance with the ratio of the read head signal time interval from a stripe of the first azimuthal orientation to a stripe of the second azimuthal orientation and the interval between two stripes of the same orientation.

5. A servo control system for positioning a magnetic head adjacent a surface of a moving magnetic storage medium for reading a servo pattern recorded in at least one track on the storage medium surface, the system comprising:

a head assembly having at least one servo read head for reading the servo pattern on the storage medium in a transducing direction and generating a read head signal representative of the servo pattern;

a servo decoder that receives the read head signal and decodes it to generate a position signal that indicates the position of the read head relative to the servo pattern;

a translation assembly that is activated to position the head assembly relative to the storage medium; and

a servo controller that activates the translation assembly in accordance with the position signal;

the servo decoder including means for decoding a read head signal produced from a servo pattern that comprises a cyclic sequence of magnetic flux transitions that extend continuously across the width of the track and define servo pattern stripes such that the servo read head signal varies as the servo read head is moved across the width of the track, the stripes including at least a first azimuthal orientation and a second azimuthal orientation, such that the first azimuthal orientation is not parallel to the second azimuthal orientation, such that the servo decoder means for decoding decodes a read head signal representative of a pattern in which the stripes are arranged in groups containing a plurality of sequential stripes at the first azimuthal orientation followed by a plurality of sequential stripes at the second azimuthal orientation.

6. A servo control system as defined in claim 5, wherein the servo decoder means for decoding decodes a read head signal produced from a servo pattern having stripes that are arranged in groups having a plurality of sequential stripes at a first orientation followed by a plurality of sequential stripes at a second orientation and that are separated by synchronization features detectable by the servo decoder.

7. A servo control system as defined in claim 6, wherein the synchronization features of the servo pattern contain information other than servo control information.

8. A servo control system as defined in claim 6, wherein the synchronization features of the servo pattern comprise transition-free spaces that are free of transitions of at least one polarity and whose minimum length in the transducing direction exceeds the maximum length in the transducing direction between consecutive transitions of that polarity within a group of stripes of the same azimuthal orientation.

9. A servo control system as defined in claim 5, wherein one or more pluralities of adjacent servo tracks on the storage medium form one or more servo track bands.

10. A servo control system as defined in claim 9, wherein adjacent servo tracks within a band are symmetric about a longitudinal centerline axis of the band.

11. A servo control system as defined in claim 5, wherein the signal decoder means for decoding detects signals from the servo read head corresponding to magnetic flux transitions having a first flux polarity and ignores magnetic flux transitions having a second flux polarity.

12. A servo control system as defined in claim 5, wherein the storage medium comprises a tape substrate having a magnetic layer in which the servo pattern is recorded.

13. A servo control system for positioning a magnetic head adjacent a surface of a moving magnetic storage medium for reading a servo pattern recorded in at least one track on the storage medium surface, the system comprising:

a head assembly having at least one servo read head for reading the servo pattern on the storage medium in a transducing direction and generating a read head signal representative of the servo pattern;

a servo decoder that receives the read head signal and decodes it to generate a position signal that indicates the position of the read head relative to the servo pattern;

a translation assembly that is activated to position the head assembly relative to the storage medium; and

a servo controller that activates the translation assembly in accordance with the position signal;

the servo decoder including means for decoding a read head signal produced from a servo pattern that comprises a cyclic sequence of magnetic flux transitions that extend continuously across the width of the track and define servo pattern stripes such that the servo read head signal varies as the servo read head is moved across the width of the track, the stripes including at least a first azimuthal orientation and a second azimuthal orientation, such that the first azimuthal orientation is not parallel to the second azimuthal orientation, such that the servo decoder means for decoding decodes a read head signal representative of a pattern in which the stripes are arranged in groups containing a plurality of sequential stripes at the first azimuthal orientation followed by a plurality of sequential stripes at the second azimuthal orientation;

wherein the servo decoder means for decoding decodes a read head signal produced from a servo pattern having stripes that are arranged in groups having a plurality of sequential stripes at a first orientation followed by a plurality of sequential stripes at a second orientation and that are separated by synchronization features detectable by the servo decoder;

wherein the synchronization features of the servo pattern comprise transition-free spaces that are free of transitions of at least one polarity and whose minimum length in the transducing direction exceeds the maximum length in the transducing direction between consecutive transitions of that polarity within a group of stripes of the same azimuthal orientation; and

wherein each pattern period of the cyclic sequence of transitions comprises a plurality of groups of stripes, each group containing stripes of a single azimuthal orientation and at least one group within a period contains a different number of stripes from the number contained within the other groups.

14. A servo control system as defined in claim 13, wherein the servo decoder means for decoding identifies individual transition-free spaces within a pattern period by counting the number of stripes detected in previous groups of stripes.

15. A servo control system as defined in claim 13, wherein each pattern period of the cyclic sequence of transitions comprises a group of four stripes at a first orientation, followed by a group of four stripes at a second orientation, followed by a group of five stripes at the first orientation, followed by a group of five stripes at the second orientation, a transition-free space occurring after each group.

16. A servo control system for positioning a magnetic head adjacent a surface of a moving magnetic storage medium for reading a servo pattern recorded in at least one track on the storage medium surface, the system comprising:

a head assembly having at least one servo read head for reading the servo pattern on the storage medium in a transducing direction and generating a read head signal representative of the servo pattern;

a servo decoder that receives the read head signal and decodes it to generate a position signal that indicates the position of the read head relative to the servo pattern;

a translation assembly that is activated to position the head assembly relative to the storage medium; and

a servo controller that activates the translation assembly in accordance with the position signal;

the servo decoder including means for decoding a read head signal produced from a servo pattern that comprises a cyclic sequence of magnetic flux transitions that extend continuously across the width of the track and define servo pattern stripes such that the servo read head signal varies as the servo read head is moved across the width of the track, the stripes including at least a first azimuthal orientation and a second azimuthal orientation, such that the first azimuthal orientation is not parallel to the second azimuthal orientation, such that the servo decoder means for decoding decodes a read head signal representative of a pattern in which the stripes are arranged in groups containing a plurality of sequential stripes at the first azimuthal orientation followed by a plurality of sequential stripes at the second azimuthal orientation;

wherein one or more pluralities of adjacent servo tracks on the storage medium form one or more servo track bands; and

wherein adjacent servo tracks on the storage medium within a band comprise patterns that are reflections of one another in a line in the transducing direction, such that all transitions in a servo track band are continuous across the width of the band.

17. A servo control system as defined in claim 16, wherein two tracks on the storage medium form a servo band that is symmetric about the center of the band in the transducing direction, each track comprising a cyclic sequence whose period is a group of four linear stripes at a first orientation, followed by a group of four linear stripes at a second orientation, followed by a group of five linear stripes at the first orientation, followed by a group of five linear stripes at the second orientation, a transition-free space occurring after each group;

and

the first and second azimuthal orientations comprise supplementary angles that are symmetric about the center of the band, such that the band comprises sequential groups of four and five chevrons of opposite direction, separated by transition-free spaces.

18. A servo control system for positioning a magnetic head adjacent a surface of a moving magnetic storage medium for reading a servo pattern recorded in at least one track on the storage medium surface, the system comprising:

a head assembly having at least one servo read head for reading the servo pattern on the storage medium in a transducing direction and generating a read head signal representative of the servo pattern;

a servo decoder that receives the read head signal and decodes it to generate a position signal that indicates the position of the read head relative to the servo pattern;

a translation assembly that is activated to position the head assembly relative to the storage medium; and

a servo controller that activates the translation assembly in accordance with the position signal;

the servo decoder including means for decoding a read head signal produced from a servo pattern that comprises a cyclic sequence of magnetic flux transitions that extend continuously across the width of the track and define servo pattern stripes such that the servo read head signal varies as the servo read head is moved across the width of the track, the stripes including at least a first azimuthal orientation and a second azimuthal orientation, such that the first azimuthal orientation is not parallel to the second azimuthal orientation and the stripes are arranged in groups containing a plurality of sequential subgroups, each subgroup containing stripes at more than one azimuthal orientation, the groups being separated by synchronization features detectable by the servo decoder.

19. A servo control system as defined in claim 18, wherein the subgroups of stripes of the servo pattern comprise pairs of stripes, each pair comprising a stripe at a first azimuthal orientation and a stripe at a second azimuthal orientation.

20. A servo control system as defined in claim 18, wherein the synchronization features of the servo pattern comprise transition-free spaces that are free of transitions of at least one polarity whose minimum length in the transducing direction exceeds the maximum length in the transducing direction between consecutive transitions of that polarity within a group of stripes of the same azimuthal orientation.

21. A servo control system as defined in claim 18, wherein the synchronization features of the servo pattern contain information other than servo control information.

22. A servo control system as defined in claim 18, wherein one or more pluralities of adjacent servo tracks on the storage medium form one or more servo track bands.

23. A servo control system as defined in claim 22, wherein adjacent servo tracks within a band are symmetric about a longitudinal centerline axis of the band.

24. A servo control system as defined in claim 18, wherein the signal decoder means for decoding detects signals from the servo read head corresponding to magnetic flux transitions having a first flux polarity and ignores magnetic flux transitions having a second flux polarity.

25. A servo control system as defined in claim 18, wherein the storage medium comprises a tape substrate having a magnetic layer in which the servo pattern is recorded.

26. A servo control system for positioning a magnetic head adjacent a surface of a moving magnetic storage medium for reading a servo pattern recorded in at least one track on the storage medium surface, the system comprising:

a head assembly having at least one servo read head for reading the servo pattern on the storage medium in a transducing direction and generating a read head signal representative of the servo pattern;

a servo decoder that receives the read head signal and decodes it to generate a position signal that indicates the position of the read head relative to the servo pattern;

a translation assembly that is activated to position the head assembly relative to the storage medium; and

a servo controller that activates the translation assembly in accordance with the position signal;

the servo decoder including means for decoding a read head signal produced from a servo pattern that comprises a cyclic sequence of magnetic flux transitions that extend continuously across the width of the track and define servo pattern stripes such that the servo read head signal varies as the servo read head is moved across the width of the track, the stripes including at least a first azimuthal orientation and a second azimuthal orientation, such that the first azimuthal orientation is not parallel to the second azimuthal orientation and the stripes are arranged in groups containing a plurality of sequential subgroups, each subgroup containing stripes at more than one azimuthal orientation, the groups being separated by synchronization features detectable by the servo decoder;

wherein one or more pluralities of adjacent servo tracks on the storage medium form one or more servo track bands; and

wherein adjacent servo tracks within a band comprise patterns that are reflections of one another in a line in the transducing direction, such that all transitions in a servo track band are continuous across the width of the band.

27. A data storage system comprising:

a magnetic storage medium having a servo pattern recorded on at least one servo track;

drive means for moving the magnetic storage medium relative to a magnetic head assembly;

a magnetic head assembly that is moved sufficiently close to a surface of the moving magnetic storage medium for reading the servo pattern recorded on the storage medium surface and for generating a servo read head signal, the magnetic head assembly including at least one data head for reading and writing data and at least one servo read head for reading servo information on tracks of the storage medium;

a servo control system for positioning the magnetic head assembly adjacent the surface of the moving magnetic storage medium for reading the servo pattern recorded in at least one track of the storage medium surface, a servo decoder that receives the servo read head signal and decodes it to generate a position signal that indicates the position of the servo read head relative to the servo pattern, a translation assembly that is activated to position the head assembly relative to the storage medium, and a servo controller that activates the translation assembly in accordance with the position signal, the servo decoder including means for decoding a servo read head signal produced from a servo pattern that comprises a cyclic sequence of magnetic flux transitions that extend continuously across the width of the track and define servo pattern stripes such that the servo read head signal varies as the magnetic head is moved across the width of the track, the stripes including at least a first azimuthal orientation and a second azimuthal orientation, such that the first azimuthal orientation is not parallel to the second azimuthal orientation and the stripes are arranged in groups containing a plurality of sequential stripes at the first azimuthal orientation followed by a plurality of sequential stripes at the second azimuthal orientation.

28. A data storage system as defined in claim 27, wherein the groups of sequential stripes at a single orientation are separated from groups of sequential stripes at other orientations by synchronization features.

29. A data storage system as defined in claim 28, wherein the synchronization features comprise transition-free spaces that are free of transitions of at least one polarity whose minimum length in the transducing direction exceeds the maximum length in the transducing direction between consecutive transitions of that polarity within a group of stripes of the same azimuthal orientation.

30. A data storage system as defined in claim 27, wherein one or more pluralities of adjacent servo tracks form one or more servo track bands.

31. A data storage system as defined in claim 30, wherein adjacent servo tracks within a band are symmetric about a longitudinal centerline axis of the band.

32. A data storage system as defined in claim 27, wherein the signal decoder detects signals from the servo read head corresponding to magnetic flux transitions having a first flux polarity and ignores magnetic flux transitions having a second flux polarity.

33. A data storage system as defined in claim 27, wherein the system further includes means for writing the servo pattern on the storage medium.

34. A data storage system comprising:

a magnetic storage medium having a servo pattern recorded on at least one servo track;

drive means for moving the magnetic storage medium relative to a magnetic head assembly;

a magnetic head assembly that is moved sufficiently close to a surface of the moving magnetic storage medium for reading the servo pattern recorded on the storage medium surface and for generating a servo read head signal, the magnetic head assembly including at least one data head for reading and writing data and at least one servo read head for reading servo information on tracks of the storage medium;

a servo control system for positioning the magnetic head assembly adjacent the surface of the moving magnetic storage medium for reading the servo pattern recorded in at least one track of the storage medium surface, a servo decoder that receives the servo read head signal and decodes it to generate a position signal that indicates the position of the servo read head relative to the servo pattern, a translation assembly that is activated to position the head assembly relative to the storage medium, and a servo controller that activates the translation assembly in accordance with the position signal, the servo decoder including means for decoding a servo read head signal produced from a servo pattern that comprises a cyclic sequence of magnetic flux transitions that extend continuously across the width of the track and define servo pattern stripes such that the servo read head signal varies as the magnetic head is moved across the width of the track, the stripes including at least a first azimuthal orientation and a second azimuthal orientation, such that the first azimuthal orientation is not parallel to the second azimuthal orientation and the stripes are arranged in groups containing a plurality of sequential stripes at the first azimuthal orientation followed by a plurality of sequential stripes at the second azimuthal orientation;

wherein the groups of sequential stripes at a single orientation are separated from groups of sequential stripes at other orientations by synchronization features;

wherein the synchronization features comprise transition-free spaces that are free of transitions of at least one polarity whose minimum length in the transducing direction exceeds the maximum length in the transducing direction between consecutive transitions of that polarity within a group of stripes of the same azimuthal orientation; and

wherein each pattern period of the cyclic sequence of transitions comprises a plurality of groups of stripes, each group containing stripes of a single azimuthal orientation and at least one group within a period contains a different number of stripes from the number contained within the other groups.

35. A data storage system as defined in claim 34, wherein the servo decoder identifies individual transition-free spaces within a pattern period by counting the number of stripes detected in previous groups of stripes.

36. A data storage system as defined in claim 34, wherein each pattern period of the cyclic sequence of transitions comprises a group of four stripes at a first orientation, followed by a group of four stripes at a second orientation, followed by a group of five stripes at the first orientation, followed by a group of five stripes at the second orientation, a transition-free space occurring after each group.

37. A data storage system as defined in claim 34, wherein the synchronization features contain information other than servo control information.

38. A data storage system comprising:

a magnetic storage medium having a servo pattern recorded on at least one servo track;

drive means for moving the magnetic storage medium relative to a magnetic head assembly;

a magnetic head assembly that is moved sufficiently close to a surface of the moving magnetic storage medium for reading the servo pattern recorded on the storage medium surface and for generating a servo read head signal, the magnetic head assembly including at least one data head for reading and writing data and at least one servo read head for reading servo information on tracks of the storage medium;

a servo control system for positioning the magnetic head assembly adjacent the surface of the moving magnetic storage medium for reading the servo pattern recorded in at least one track of the storage medium surface, a servo decoder that receives the servo read head signal and decodes it to generate a position signal that indicates the position of the servo read head relative to the servo pattern, a translation assembly that is activated to position the head assembly relative to the storage medium, and a servo controller that activates the translation assembly in accordance with the position signal, the servo decoder including means for decoding a servo read head signal produced from a servo pattern that comprises a cyclic sequence of magnetic flux transitions that extend continuously across the width of the track and define servo pattern stripes such that the servo read head signal varies as the magnetic head is moved across the width of the track, the stripes including at least a first azimuthal orientation and a second azimuthal orientation, such that the first azimuthal orientation is not parallel to the second azimuthal orientation and the stripes are arranged in groups containing a plurality of sequential stripes at the first azimuthal orientation followed by a plurality of sequential stripes at the second azimuthal orientation;

wherein one or more pluralities of adjacent servo tracks form one or more servo track bands; and

wherein adjacent servo tracks within a band comprise patterns that are reflections of one another in a line in the transducing direction, such that all transitions in a servo track band are continuous across the width of the band.

39. A, data storage system as defined in claim 38, wherein two tracks form a servo band that is symmetric about the center of the band in the transducing direction, each track comprising a cyclic sequence whose period is a group of four linear stripes at a first orientation, followed by a group of four linear stripes at a second orientation, followed by a group of five linear stripes at the first orientation, followed by a group of five linear stripes at the second orientation, a transition-free space occurring after each group;

and

the first and second azimuthal orientations comprise supplementary angles that are symmetric about the center of the band, such that the band comprises sequential groups of four and five chevrons of opposite direction, separated by transition-free spaces.

40. A data storage system comprising:

a magnetic storage medium having a servo pattern recorded on at least one servo track;

drive means for moving the magnetic storage medium relative to a magnetic head assembly;

a magnetic head assembly that is moved sufficiently close to a surface of the moving magnetic storage medium for reading the servo pattern recorded on the storage medium surface and for generating a servo read head signal, the magnetic head assembly including at least one data head for reading and writing data and at least one servo read head for reading servo information on tracks of the storage medium;

a servo control system for positioning the magnetic head assembly adjacent the surface of the moving magnetic storage medium for reading the servo pattern recorded in at least one track of the storage medium surface, a servo decoder that receives the servo read head signal and decodes it to generate a position signal that indicates the position of the read head relative to the servo pattern, a translation assembly that is activated to position the head assembly relative to the storage medium, and a servo controller that activates the translation assembly in accordance with the position signal, wherein;

the servo decoder includes means for decoding a servo read head signal produced from a servo pattern that comprises a cyclic sequence of magnetic flux transitions that extend continuously across the width of the track and define servo pattern stripes such that the servo read head signal varies as the magnetic head is moved across the width of the track, the stripes including at least a first azimuthal orientation and a second azimuthal orientation, such that the first azimuthal orientation is not parallel to the second azimuthal orientation and the stripes are arranged in groups containing a plurality of sequential subgroups, each subgroup containing stripes at more than one azimuthal orientation, the groups being separated by synchronization features.

41. A data storage system comprising:

a magnetic storage medium having a servo pattern recorded on at least one servo track;

drive means for moving the magnetic storage medium relative to a magnetic head assembly;

a magnetic head assembly that is moved sufficiently close to a surface of the moving magnetic storage medium for reading the servo pattern recorded on the storage medium surface and for generating a servo read head signal, the magnetic head assembly including at least one data head for reading and writing data and at least one servo read head for reading servo information on tracks of the storage medium;

a servo control system for positioning the magnetic head assembly adjacent the surface of the moving magnetic storage medium for reading the servo pattern recorded in at least one track of the storage medium surface, a servo decoder that receives the servo read head signal and decodes it to generate a position signal that indicates the position of the servo read head relative to the servo pattern, a translation assembly that is activated to position the head assembly relative to the storage medium, and a servo controller that activates the translation assembly in accordance with the position signal, wherein the servo decoder includes means for decoding a read head signal produced from a servo pattern that comprises a cyclic sequence of magnetic flux transitions that extend continuously across the width of the track and define servo pattern stripes such that the servo read head signal varies as the magnetic head is moved across the width of the track, the stripes including at least a first azimuthal orientation and a second azimuthal orientation, such that the first azimuthal orientation is not parallel to the second azimuthal orientation and the servo decoder determines the time intervals between a plurality of predetermined pairs of transitions in the servo pattern and generates a substantially speed invariant position signal that is a function of the time intervals.

42. A data storage system as defined in claim 41, wherein the signal decoder means for decoding detects signals from the read head corresponding to magnetic flux transitions having a first flux polarity and ignores magnetic flux transitions having a second flux polarity.

43. A data storage system comprising:

a magnetic storage medium having a servo pattern recorded on at least one servo track;

drive means for moving the magnetic storage medium relative to a magnetic head assembly;

a magnetic head assembly that is moved sufficiently close to a surface of the moving magnetic storage medium for reading the servo pattern recorded on the storage medium surface and for generating a servo read head signal, the magnetic head assembly including at least one data head for reading and writing data and at least one servo read head for reading servo information on tracks of the storage medium; and

a servo control system for positioning the magnetic head assembly adjacent the surface of the moving magnetic storage medium for reading the servo pattern recorded in at least one track of the storage medium surface, a servo decoder that receives the servo read head signal and decodes it to generate a position signal that indicates the position of the servo read head relative to the servo pattern, a translation assembly that is activated to position the head assembly relative to the storage medium, and a servo controller that activates the translation assembly in accordance with the position signal, wherein the servo decoder includes means for decoding a read head signal produced from a servo pattern that comprises a cyclic sequence of magnetic flux transitions that extend continuously across the width of the track and define servo pattern stripes such that the servo read head signal varies as the magnetic head is moved across the width of the track, the stripes including at least a first azimuthal orientation and a second azimuthal orientation, such that the first azimuthal orientation is not parallel to the second azimuthal orientation and the servo decoder determines the time intervals between a plurality of predetermined pairs of transitions in the servo pattern and generates a substantially speed invariant position signal that is a function of the time intervals; and

wherein the servo decoder means for decoding generates a position signal value in accordance with the ratio of the read head signal time interval from a stripe of the first azimuthal orientation to a stripe of the second azimuthal orientation and the interval between two stripes of the same orientation.