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Copy protected disk

  • US 4,823,210 A
  • Filed: 08/13/1984
  • Issued: 04/18/1989
  • Est. Priority Date: 08/13/1984
  • Status: Expired due to Fees
First Claim
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1. In a copy protected magnetic storage disk having a magnetic recording layer including a plurality of record tracks suitable for recording information-bearing data accompanied by a clock signal comprising a sequence of uniformly spaced pulses having a signal strength comparable to the signal strength of the information-bearing data, the clock signal being represented on a magnetic recording layer of a magnetic disk by a series of transitions that occur at the frequency of the clock signal pulses, the improvement comprising:

  • (a) at least one of the record tracks including a control pattern of magnetic transitions, recorded at a predetermined location on the recording layer of the disk, representative of a code burst derived by temporarily changing the frequency of the pulses of the clock signal during a recording operation, the frequency of the transitions of the control pattern being beyond the frequency capability of an associated playback device, to cause, in response to the playing back of the control pattern, random playback data to be produced which are dissimilar from one playback operation to the next playback operation;

    (b) the recording layer including a plurality of radially arrayed sectors wherein the code burst follows a data sync gap in a predetermined recording track of one of said sectors; and

    (c) a serial number is encoded about the predetermined recording track following the code burst.

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