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Copy protection for computer discs

  • US 4,849,836 A
  • Filed: 07/24/1986
  • Issued: 07/18/1989
  • Est. Priority Date: 06/07/1985
  • Status: Expired due to Fees
First Claim
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1. A method of protecting a computer disc against copying, said disc containing information enabling the running of a computer program, and a data set providing an indication of copy legitimacy by causing inconsistent readouts when read repeatedly, said method comprising the steps of:

  • (a) recording on said disc a set of data of which different portions are recorded at different phase angles;

    (b) causing said data set to be read repeatedly;

    (c) causing successive readouts of said data to be compared to one another;

    (d) structuring said program so that it cannot be run if said successive read-outs are consistent with one another;

    (e) said data set being a repetitive series of words, and said different portions being predetermined transitions within words;

    (f) said words of said data set including a bit sequence of two bits containing a single transition signifying a logic "1", and the phase angle of said transition being incrementally shifted in each repetition of said words within said series so as to gradually vary said bit sequence between "10" and "01";

    (g) said bit sequence being flanked by a logic "1" on each side thereof to avoid loss of synchronization in the event that said bit sequence is spuriously read as "00".

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