Non Return to Zero Inverted

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Non Return to Zero Inverted (usually given as the acronym, NRZI) is an encoding technique which is commonly used on magnetic storage.

In NRZI, whether a particular bit is '0' or '1' is indicated by the presence or absence of a level transition at each clock time.

The disadvantage of NRZI is that a long strings of whichever value does not cause a level transition makes it hard to make sure that the clock stays in synchronization. For this reason, many NRZI encooding systems make use of either bit stuffing or run-length limited coding to limit the maximum number of transition-less bit times.