A report on Non-return-to-zero and Group coded recording

The binary signal is encoded using rectangular pulse-amplitude modulation with polar NRZ(L), or polar non-return-to-zero-level code
Unipolar NRZ(L), or unipolar non-return-to-zero level
Non-return-to-zero space
Encoder for NRZS, toggle on zero
An example of the NRZI encoding, transition on 1
The opposite convention, transition on 0
Encoder for NRZI, toggle on one

GCR is a modified form of a NRZI code, but necessarily with a higher transition density.

- Group coded recording

Synchronized NRZI (NRZI-S, SNRZI) and group-coded recording (GCR) are modified forms of NRZI.

- Non-return-to-zero
The binary signal is encoded using rectangular pulse-amplitude modulation with polar NRZ(L), or polar non-return-to-zero-level code

1 related topic with Alpha

Overall
An example of Manchester encoding showing both conventions for representation of data

Manchester code

0 links

Line code in which the encoding of each data bit is either low then high, or high then low, for equal time.

Line code in which the encoding of each data bit is either low then high, or high then low, for equal time.

An example of Manchester encoding showing both conventions for representation of data

Manchester code was widely used for magnetic recording on 1600 bpi computer tapes before the introduction of 6250 bpi tapes which used the more efficient group-coded recording.

The price of these benefits is a doubling of the bandwidth requirement compared to simpler NRZ coding schemes.