Duplication item distinction method and its device and duplication item reading prevention method null of

摘要

PURPOSE:To prevent substantially both the reproduction of a floppy disk and the rewriting of a data field part by recording an ID field part and a data field part continuously to a floppy disk serving as an original text and detecting a shift of phase at a junction between both field parts to decide the identity of the original text. CONSTITUTION:A shift of bit is produced in the read data obtained at and after the junction between the start and end points of a data field part owing to a shift of phase at the junction. Thus it is possible to decide whether a floppy disk is identical with an original text or a copy or obtained by rewriting the data contents of the original text by detecting whether or not a shift of bit is produced in a data read mode. It is also possible to detect the bit shift by comparing the read-out information on the floppy disk with the information on the original text stored previously. The probability showing the phase shifts produced at the start and end points of the data field part is equal to 1/8 per sector. Thus a large number of sectors to be checked provide higher accuracy.