Disk drive using multiple servo timing marks that form a code of unique interrelated bit patterns

• US 5,903,410 A
• Filed: 03/24/1997
• Issued: 05/11/1999
• Est. Priority Date: 03/24/1997
• Status: Expired due to Term

• Current Assignee: Western Digital Technologies Incorporated (Western Digital Corporation)
• Original Assignee: International Business Machines Corporation
• Inventors: Hetzler, Steven Robert, Blaum, Mario, Kabelac, William John
• Primary Examiner(s): Edun, Muhammad N.
• Application Number:
  US08/823,435
• Time in Patent Office: 778 Days
• Field of Search: 360/77.08, 360/77.11, 360/77.07, 360/77.06, 360/77.05, 360/77.02, 360/77.01, 360/75, 360/69, 360/53, 360/48, 360/51, 360/39, 360/78.04, 360/78.14
• US Class Current: 360/77.08
• CPC Class Codes: G11B 20/1258 where blocks are arranged within multiple radial zones, e.g. Zone Bit Recording or Constant Density Recording discs, MCAV discs, MCLV discs
• CPC Class Codes: G11B 20/1813 by adding special bits or symbols to the coded information G11B20/1809 takes precedence
• CPC Class Codes: G11B 21/083 on discs
• CPC Class Codes: G11B 21/085 with track following of accessed part
• CPC Class Codes: G11B 5/59605 Circuits G11B5/59627 - G11B5/59688 take precedence
• CPC Class Codes: G11B 5/59655 Sector, sample or burst servo format
• CPC Class Codes: G11B 7/00745 Sectoring or header formats within a track formats in general G11B20/12

Abstract

A data recording disk drive has a plurality of servo sectors containing error-detectable and error-correctable servo timing marks (STMs). Each STM is represented as a pattern of n bits of digital information, with each track having a set of m unique STM patterns, and wherein each of the m unique STM patterns of n bits has a minimum sliding distance d to every other STM pattern in the set, where d is greater than one. The error-tolerant STMs are achieved by the use of a set or code of fixed STM bit patterns, where the STM patterns have a specified minimum Hamming distance against all the patterns in the search, called the sliding distance d. These STM patterns may include any bits associated with the servo sectors, such as bits indicating track index, servo sector number, and recording head number. The disk drive includes STM decoding circuitry that recognizes valid STMs when the sliding distance between the repeating preamble pattern and the STM patterns are within predetermined limits defined by the power of the code. The disk drive allows a tradeoff between error correction power and error detection power, within the limits defined by the code. The STM decoding circuitry is adaptive by allowing the error correction and error detection comparison values to be updatable.

Claims

1. A data recording disk drive that has a recording disk and a recording head that reads information from the disk, the disk drive comprising:

a disk having a plurality of tracks, each track having a plurality of servo sectors containing servo information for determining recording head position, each of the servo sectors also containing a servo timing mark (STM) recorded on the disk and being represented as a pattern of n bits of digital information, each of the tracks having a set of m unique STM patterns, where m is greater than one;

a motor for rotating the disk;

a recording head which reads information in the servo sectors;

an actuator connected to the head for positioning the head to different tracks and maintaining the head on the tracks;

an STM decoder for detecting each of the m unique STM patterns read by the head as the disk rotates to thereby signal the presence of servo sectors; and

servo electronics coupled to the STM decoder for controlling the actuator in response to servo information read by the head from the servo sectors after detection of the STMs by the STM decoder; and

wherein each of the m unique STM patterns of n bits has a minimum sliding distance d to every other STM pattern in the set, where d is greater than one.

2. The disk drive according to claim 1 wherein the disk is a magnetic recording disk, and wherein the tracks are generally concentric and also have a plurality of data sectors interspersed with the servo sectors.

3. The disk drive according to claim 1 wherein one of the STMs in the set is an index STM representing a unique location on the track.

4. The disk drive according to claim 2 wherein one of the index STMs represents the start of the track.

5. The disk drive according to claim 1 wherein one of the STMs in the set is an even sector number STM representing an even-numbered servo sector and another of the STMs in the set is an odd sector number STM representing an odd-numbered servo sector.

6. The disk drive according to claim 1 wherein a plurality of the STM patterns are arranged such that each of the STM patterns represents a portion of the servo sector number in which the STM pattern is located.

7. The disk drive according to claim 1 wherein a plurality of the STM patterns are arranged such that each of the STM patterns represents a portion of the number of the recording head associated with the disk on which the STM patterns are recorded.

8. The disk drive according to claim 1 wherein a plurality of the STM patterns are arranged such that each of the STM patterns represents a portion of the number of the track in which the STM patterns are recorded.

9. The disk drive according to claim 1 wherein each of the servo sectors also includes a preamble pattern, and wherein each of the m unique STM patterns of n bits has a minimum sliding distance d to the concatenation of the preamble pattern and each of the STM patterns.

10. The disk drive according to claim 1 wherein the preamble pattern is an automatic gain control (AGC) pattern.

11. The disk drive according to claim 1 wherein the sliding distance d is to single bit errors, and wherein the STM decoder includes means for correctly identifying each of the m STM patterns in the presence of up to s bits in error in the bits read from the head which contain the concatenation of a preamble pattern with one of the STM patterns, where s represents the STM error correction power of the set of m unique STM patterns and is less than or equal to (d-1)/2.

12. The disk drive according to claim 11 wherein the STM decoder further comprises a shift register for converting serial bits of the STM patterns read by the head into n parallel bits, storage means for storing fixed bit patterns corresponding to the m unique STM patterns in the set, means for determining the exclusive OR of the output of the shift register with the fixed STM bit patterns, and means for generating an STM found signal when the number of ones in the exclusive OR'"'"'ed output is less than or equal to s.

13. The disk drive according to claim 12 wherein the STM decoder further comprises means for generating an STM corrected error signal when the number of ones in the exclusive OR'"'"'ed output is greater than zero and less than or equal to s, said STM corrected error signal representing a correctly identified STM pattern having one of more bits in error.

14. The disk drive according to claim 13 wherein the STM decoder further comprises means for logging the number of STM corrected error signals generated during a predetermined time interval.

15. The disk drive according to claim 13 wherein the STM decoder further comprises means for generating an STM corrected error count signal corresponding to the number of ones in the exclusive OR output when the number of 1'"'"'s is greater than zero and less then or equal to s.

16. The disk drive according to claim 15 wherein the STM decoder further comprises means for logging the STM corrected error count values in a predetermined time interval.

17. The disk drive according to claim 12 wherein s=(d-1)/2, and wherein the STM decoder further comprises means for generating an STM missed signal when the number of ones in the exclusive OR'"'"'ed output remains greater than s during a predetermined time window.

18. The disk drive according to claim 12 wherein the STM decoder further comprises a programmable storage means for storing the value s, whereby the STM error correction power may be modified in the disk drive.

19. The disk drive according to claim 12 wherein the storage means for storing the fixed STM patterns is programmable, whereby the fixed STM patterns may be modified in the disk drive.

20. The disk drive according to claim 12 wherein the shift register includes a preloaded pattern.

21. The disk drive according to claim 20 wherein the preloaded pattern is a preamble pattern.

22. The disk drive according to claim 1 wherein the STM decoder includes means for correcting up to s bits in error in each of the m STM patterns, and means for detecting without correcting up to s+t bits in error in each of the m STM patterns, where (2s+t) is less than or equal to (d-1).

23. The disk drive according to claim 22 wherein the STM decoder further comprises a shift register for converting serial bits read by the head into n parallel bits, storage means for storing bit patterns corresponding to the m unique STM patterns in the set, means for determining the exclusive OR of the output of the shift register with the fixed STM bit patterns, and means for generating an STM found signal when the number of ones in the exclusive OR'"'"'ed output is less than or equal to s.

24. The disk drive according to claim 23 wherein the STM decoder further comprises means for generating an STM corrected error count signal corresponding to the number of ones in the exclusive OR output, when the number of ones is greater than zero and less than or equal to s.

25. The disk drive according to claim 24 wherein the STM decoder further comprises means for logging the STM corrected error count values in a predetermined time interval.

26. The disk drive according to claim 23 wherein the STM decoder further comprises means for generating an STM uncorrectable error signal when the number of ones in the exclusive OR'"'"'ed output is greater than s, but less than or equal to s+t.

27. The disk drive according to claim 23 wherein the STM decoder further comprises means for generating an STM missed signal when the number of ones in the exclusive OR'"'"'ed output remains greater than s+t for a predetermined time window.

28. The disk drive according to claim 22 wherein the STM decoder further comprises a programmable storage means for storing the value s, whereby the STM error correction power may be modified in the disk drive.

29. The disk drive according to claim 22 wherein the storage means for storing the fixed STM patterns is programmable, whereby the STM patterns may be modified in the disk drive.

30. The disk drive according to claim 1 wherein the sliding distance d is to bursts of up to b consecutive bits in error, and wherein the STM decoder includes means for correctly identifying each of the m STM patterns in the presence of up to s bursts of up to b consecutive bits in error in the data read from the head which contain the concatenation of a preamble pattern with one of the STM patterns, where s represents the STM burst error correction power for bursts up to b bits and is less than or equal to (d-1)/2.

31. The disk drive according to claim 1 wherein the STM decoder includes a set of at least m registers for holding the m STM patterns.

32. The disk drive according to claim 31 wherein the STM decoder includes a register for selecting a number of STM patterns different from the number of STM pattern registers.

33. The disk drive according to claim 31 wherein the STM decoder includes a register for selecting the level of correction or detection.

34. The disk drive according to claim 33 wherein the register for selecting the level of correction or detection stores the correction value s.

35. The disk drive according to claim 33 wherein the disk drive includes means for retrying to read STMs, and wherein the level of correction or detection in the register for selecting the level of correction or detection is selected in response to an STM read retry.

36. The disk drive according to claim 33 wherein the level of correction or detection in the register for selecting the level of correction or detection is selected in response to the number of stored bits in error.

37. A fixed-block architecture embedded servo magnetic recording disk drive that has a magnetic recording disk and a recording head that reads information from and writes information to the disk, the disk drive comprising:

a magnetic recording disk having a plurality of generally concentric data tracks, each track being divided into a plurality of data sectors and a plurality of angularly-spaced servo sectors containing servo information for determining recording head position, each of the servo sectors also containing a servo timing mark (STM) recorded ont he disk and being represented as a pattern of n bits of digital information, each of the tracks having a set of m unique STM patterns, where m is greater than one;

a motor for rotating the disk;

a recording head which reads information in the servo sectors and which writes and reads user data in the data sectors;

an actuator connected to the head for positioning the head to different data tracks and maintaining the head on the data tracks during read and write operations;

an STM decoder for detecting each of the m unique STM patterns read by the head as the disk rotates to thereby signal the presence of servo sectors; and

servo electronics coupled to the STM decoder for controlling the actuator in response to servo information read by the head from the servo sectors after detection of the STMs by the STM decoder; and

wherein each of the m unique STM patterns of n bits has a minimum sliding distance d to every other STM pattern in the set, where d is greater than one.

38. The disk drive according to claim 37 wherein one of the STMs in the set is an index STM representing the start of the data track.

39. The disk drive according to claim 37 wherein one of the STMs in the set is an even sector number STM representing an even-numbered servo sector and another of the STMs in the set is an odd sector number STM representing an odd-numbered servo sector.

40. The disk drive according to claim 37 wherein a plurality of the STM patterns are arranged such that each of the STM patterns represents a portion of the servo sector number in which the STM pattern is located.

41. The disk drive according to claim 37 wherein a plurality of the STM patterns are arranged such that each of the STM patterns represents a portion of the number of the recording head associated with the disk on which the STM patterns are recorded.

42. The disk drive according to claim 37 wherein a plurality of the STM patterns are arranged such that each of the STM patterns represents a portion of the number of the data track in which the STM patterns are recorded.

43. The disk drive according to claim 37 wherein each of the servo sectors also includes an automatic gain control (AGC) pattern, and wherein each of the m unique STM patterns of n bits has a minimum sliding distance d to the AGC pattern.

44. The disk drive according to claim 37 wherein the sliding distance d is to single bit errors, and wherein the STM decoder includes means for correctly identifying each of the m STM patterns in the presence of up to s bits in error in the bits read from the head which contain the concatenation of a preamble pattern with one of the STM patterns, where s represents the STM error correction power of the set of m unique STM patterns and is less than or equal to (d-1)/2.

45. The disk drive according to claim 44 wherein the STM decoder further comprises a shift register for converting serial bits of the STM patterns read by the head into n parallel bits, storage means for storing fixed bit patterns corresponding to the m unique STM patterns in the set, means for determining the exclusive OR of the output of the shift register with the fixed STM bit patterns, and means for generating an STM found signal when the number of ones in the exclusive OR'"'"'ed output is less than or equal to s.

46. The disk drive according to claim 45 wherein the STM decoder further comprises means for generating an STM corrected error signal when the number of ones in the exclusive OR'"'"'ed output is greater than zero and less than or equal to s, said STM corrected error signal representing a correctly identified STM pattern having one of more bits in error.

47. The disk drive according to claim 46 wherein the STM decoder further comprises means for logging the number of STM corrected error signals generated during a predetermined time interval.

48. The disk drive according to claim 46 wherein the STM decoder further comprises means for generating an STM corrected error count signal corresponding to the number of ones in the exclusive OR output when the number of 1'"'"'s is greater than zero and less then or equal to s.

49. The disk drive according to claim 48 wherein the STM decoder further comprises means for logging the STM corrected error count values in a predetermined time interval.

50. The disk drive according to claim 45 wherein s=(d-1)/2, and wherein the STM decoder further comprises means for generating an STM missed signal when the number of ones in the exclusive OR'"'"'ed output remains greater than s during a predetermined time window.

51. The disk drive according to claim 44 wherein the STM decoder further comprises a programmable storage means for storing the value s, whereby the STM error correction power may be modified in the disk drive.

52. The disk drive according to claim 44 wherein the storage means for storing the fixed STM patterns is programmable, whereby the fixed STM patterns may be modified in the disk drive.

53. The disk drive according to claim 37 wherein the STM decoder includes means for correcting up to s bits in error in each of the m STM patterns, and means for detecting without correcting up to s+t bits in error in each of the m STM patterns, where (2s+t) is less than or equal to (d-1).

54. The disk drive according to claim 53 wherein the STM decoder further comprises a shift register for converting serial bits read by the head into n parallel bits, storage means for storing bit patterns corresponding to the m unique STM patterns in the set, means for determining the exclusive OR of the output of the shift register with the fixed STM bit patterns, and means for generating an STM found signal when the number of ones in the exclusive OR'"'"'ed output is less than or equal to s.

55. The disk drive according to claim 54 wherein the STM decoder further comprises means for generating an STM corrected error count signal corresponding to the number of ones in the exclusive OR output when the number of ones is greater than zero and less than or equal to s.

56. The disk drive according to claim 55 wherein the STM decoder further comprises means for logging the STM corrected error count values in a predetermined time interval.

57. The disk drive according to claim 54 wherein the STM decoder further comprises means for generating an STM uncorrectable error signal when the number of ones in the exclusive OR'"'"'ed output is greater than s, but less than or equal to s+t.

58. The disk drive according to claim 54 wherein the STM decoder further comprises means for generating an STM missed signal when the number of ones in the exclusive OR'"'"'ed output remains greater than s+t for a predetermined time window.

59. The disk drive according to claim 53 wherein the STM decoder further comprises a programmable storage means for storing the value s, whereby the STM error correction power may be modified in the disk drive.

60. The disk drive according to claim 53 wherein the storage means for storing the fixed STM patterns is programmable, whereby the STM patterns may be modified in the disk drive.

61. The disk drive according to claim 37 wherein the sliding distance d is to bursts of up to b consecutive bits in error, and wherein the STM decoder includes means for correctly identifying each of the m STM patterns in the presence of up to s bursts of up to b consecutive bits in error in the data read from the head which contain the concatenation of a preamble pattern with one of the STM patterns, where s represents the STM burst error correction power for bursts up to b bits and is less than or equal to (d-1)/2.