Non Return to Zero Inverted
From Computer History Wiki
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 encoding systems make use of either bit stuffing or run-length limited coding to limit the maximum number of transition-less bit times.
