Source : Free On-Line Dictionary of Computing

Non Return to Zero Inverted
     
         (NRZI) A recording method used for 9-track {magnetic
        tapes} (200 and 800 BPI) where a zero is represented by a
        change in the signal and a one by no change.
     
        NRZI is also used extensively in {SDLC} communications.
        {VTAM} has a parameter NRZI=YES|NO.
     
        Compare {Phase Encoded}, {GCR}.
     
        (1999-01-11)