Classifications

• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
  • G11B5/48—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed
  • G11B5/58—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed with provision for moving the head for the purpose of maintaining alignment of the head relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
  • G11B5/596—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed with provision for moving the head for the purpose of maintaining alignment of the head relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following for track following on disks
  • G11B5/59633—Servo formatting
  • G11B5/59655—Sector, sample or burst servo format
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B27/00—Editing; Indexing; Addressing; Timing or synchronising; Monitoring; Measuring tape travel
  • G11B27/10—Indexing; Addressing; Timing or synchronising; Measuring tape travel
  • G11B27/19—Indexing; Addressing; Timing or synchronising; Measuring tape travel by using information detectable on the record carrier
  • G11B27/28—Indexing; Addressing; Timing or synchronising; Measuring tape travel by using information detectable on the record carrier by using information signals recorded by the same method as the main recording
  • G11B27/30—Indexing; Addressing; Timing or synchronising; Measuring tape travel by using information detectable on the record carrier by using information signals recorded by the same method as the main recording on the same track as the main recording
  • G11B27/3027—Indexing; Addressing; Timing or synchronising; Measuring tape travel by using information detectable on the record carrier by using information signals recorded by the same method as the main recording on the same track as the main recording used signal is digitally coded

Definitions

• the present invention relates to a method for recording a unit distance track identification code and, more particularly, to a method for recording a unit distance track identification code on a magnetic disc which preserves the unit distance characteristics of the code.
• a typical disc storage system includes a number of discs coated with a suitable magnetic material mounted for rotation on a common spindle and a set of transducer heads carried in pairs on elongated supports for insertion between adjacent discs, the heads of each pair facing in opposite directions to engage opposite faces of adjacent discs.
• the support structure is coupled to a positioner motor, the positioner motor typically including a coil mounted within a magnetic field for linear movement and oriented relative to the discs to move the heads radially over the disc surfaces to thereby enable the heads to be positioned over any annular track on the surfaces.
• the positioner motor in response to control signals from the computer, positions the transducer heads radially for recording data signals on or retrieving data signals from a preselected one of a set of concentric recording tracks on the discs.
• each track crossing can be detected by the track following circuitry no matter how fast the head carriage might be moving. For this reason, track identifica ion information can be derived by simply decrementing a track difference counter until the difference is equal to zero, meaning that the transducer head has arrived at the desired trac .
• a unit distance code commonly referred to as a Gray code.
• Gray code a unit distance code
• NRZ or MFM magnetic recording codes
• ambiguities arise on track boundaries, causing uncertainties of more than one bit, and destroying the required unit distance feature of the Gray code. This can be seen most clearly from FIGURES 1, 2, 3 and 4.
• FIGURE 1 shows the data that it is desired to record at the beginning of each sector in four consecutive tracks on the surface of a magnetic disc. For purposes of the present example, these tracks are identified by the numbers 2, 1, 0 and 15.
• FIGURE 1 also shows four consecutive bit cells and the "ones" and "zeros" which are to be recorded therein.
• the track identification code is a unit distance code, i.e., only one bit of the code changes as a boundary between tracks is crossed.
• FIGURE 2 first shows the actual transitions that would be recorded on the tracks on the disc for NR2. encoding. It is seen that a "one" is indicated by a transition whereas a “zero” is indicated by no transition.
• Superimposed on tracks 2 and 1 are three possible positions of a transducer head, signified by A, B, and C. It is seen that when in position A, the transducer head is exactly aligned with track 2. When in position C, the transducer head is exactly aligned with track 1. When in position B, the transducer head is positioned midway between tracks 2 and 1. This convention will be used in each of the figures to follow.
• FIGURE 2 also shows the signals 21, 22 and 23 which are derived from the head when in positions A, B and C, respectively. It is seen that when in position A, the magnetic transitions at 24 and 25 are detected at 26 and 27, respectively, and that when in position C, the magnetic transition at 28 is detected at 29. However, when the transducer head is in position B, the transition at 24 is still detected at 30, but the transitions at 25 and 28 cancel. Accordingly, the track positioning system will decode a position 0010 which obviously has no relevance to the actual track position.
• FIGURE 3 shows the manner in which the Gray code binary data of FIGURE 1 would be recorded for FM encoding where there is a clock transition at each cell boundary and a transition in the middle of a cell to indicate the presence of a "one".
• FIGURE 3 also shows the signals 31, 32 and 33 derived from the transducer head when it is in positions A, B and C, respectively. Again it is seen that ambiguity results in the cell where there is a data bit change.
• the transitions at 34 and 35 are detected at 36 and 37, rspectively, and when in position C, the transitions at 38 and 39 are detected at 40 and 41, respectively.
• the transitions at 34 and 38 cancel and the transitions at 35 and 39 cancel so that the clock transition at the cell boundary cancels as well as the mid-cell transition. This is an illegal FM signal which cannot be interpreted by the decoding circuitry.
• FIGURE 4 shows the manner in which the binary data of FIGURE 1 would be recorded for MFM encoding where a transition at a mid-cell indicates a "one" and there is a clock transition at each cell boundary, except adjacent a "one".
• superimposed on tracks 2 and 1 are the possible head positions A, B and C.
• the signals 51, 52 and 53 which are derived when the head is in positions A, B and C, respectively.
• the transition at 54 is detected at 55 and when in position C, the transition at 56 is detected at 57.
• transitions are detected at both 54 and 56, as shown at 58 and 59, and this is an illegal signal which cannot be decoded by the decoding circuitry.
• a method for recording a unit distance track identification code on a magnetic disc which solves these problems in a manner unknown heretofore.
• the present recording technique completely eliminates ambiguities on track boundaries so that the decoding circuitry will know exactly between which tracks it is located. This is achieved simply and efficiently and in a manner which substantially simplifies the decoding circuitry required.
• a disc having opposed surfaces, at least one of the surfaces being coated with a magnetic material, the disc being adapted to be mounted on a spindle for rotation relative to a magnetic transducer positioned for recording data on and retrieving data from the surface, a plurality of concentric annular tracks being defined on the surface of the disc, each of the tracks being divided into a plurality of sectors, each such sector having associated therewith prerecorded data for identification thereof, the prerecorded identification data including a track identification code, the track identification code being a unit distance code, there is disclosed an improvement wherein the code has a first uni-directional clock transition at a fixed time in each bit cell and a second uni-directional transition at a variable time in each cell, the time of the second transition relative to the first transition determining whether the data bit is a one or a zero.
• An advantage to be derived is the preservation of the unit distance characteristics of the recorded code. Another advantage is the preservation of the required single track ambiguity. Still another advantage is the elimination of the introduction of additional uncertainties. Still another advantage is the elimination of illegal codes.
• FIGURE 1 shows diagrammatically the binary data to be recorded on a disc surface
• FIGURE 2 shows diagrammatically the manner in which the data of FIGURE 1 would be recorded on a disc utilizing NRZ encoding and the signals which will be derived from a transducer head positioned over such a disc in the positions A, B and C;
• FIGURE 3 shows diagrammatically the manner in which the- data of FIGURE 1 would be recorded on a disc utilizing FM encoding and the signals which will be derived from a transducer head positioned over such a disc in the positions A, B and C;
• FIGURE 4 shows diagrammatically the manner in which the data of FIGURE 1 would be recorded on a disc utilizing MFM encoding and the signals which will be derived from a transducer head positioned over such a disc in the positions A, B and C;
• FIGURE 5 shows diagrammatically the manner in which the data of FIGURE 1 would be recorded on a disc utilizing the teachings of the present invention and the signals which will be derived from a transducer head positioned over such a disc in the positions A, B and C.
• FIGURE 5 there is shown the preferred embodiment of encoding which will preserve the characteristics of a unit distance code.
• the recorded transitions must change only one transition or group of transitions from one track to the next. It is also desirable to have a transition per bit, minimum, in order to make decoding easy. These considerations lead to a code including a mandatory clock transition plus a mandatory data transition whose position determines whether the bit is a one or a zero.
• the mandatory clock transition is a uni-directional clock transition at a fixed time in each bit cell and the data transition is also a uni-directional transition at a variable time in each bit cell, the time of the second transition relative to the first transition determining whether the data bit is a one or a zero.
• the implementation shown is a 1/3-2/3 code.
• each bit cell begins and ends with a transition and that such transition is always in the same direction.
• every track has a transition, as shown at 61, at a fixed time in each bit cell.
• each bit cell has a second uni-directional transition which is either 1/3 of a bit cell after a clock transition for a one or 2/3 of a bit cell after a clock transition for a zero. The significance of this can be seen in comparing the signals 62, 63 and 64 derived from a transducer head when in positions A, B and C, respectively.
• the head will receive the exact same signal except in the bit cell where there is possible ambiguity.
• this cell namely the third cell
• the transitions at 61A, 65 and 61B will be detected at 66, 67 and 68, respectively
• position C the transitions at 61C, 69 and 61D, will be detected at 70, 71 and 72, respectively.
• the detected signals at 66 and 70 will add, as shown at 73
• the detected signals at 68 and 72 will add, as shown at 74.
• the decoding circuitry may decode either a one or a zero.
• the decoding circuitry will, therefore, readily decode 00?1, which can be clearly interpreted to indicate that the transducer head is between tracks 2 and 1. Thus, not only is decoding permitted, but any ambiguity can in fact be utilized to indicate to the decoding circuitry exactly where the transducing head is located.

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• Signal Processing For Digital Recording And Reproducing (AREA)

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• 1982
  • 1982-04-01 GB GB08317981A patent/GB2121654A/en not_active Withdrawn
  • 1982-04-01 EP EP19820901280 patent/EP0093713A4/de not_active Withdrawn
  • 1982-04-01 BR BR8207978A patent/BR8207978A/pt unknown
  • 1982-04-01 WO PCT/US1982/000386 patent/WO1983001859A1/en not_active Application Discontinuation
  • 1982-04-01 JP JP82501418A patent/JPS58501879A/ja active Pending

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