Nonreturn to Zero (NRZ) Definition/Meaning:
Nonreturn to Zero is way of encoding binary signals that aims to
achieve the highest possible data transfer rate for a given signal frequency.
The name is derived from the principle of operation, i.e. the signal line does
not return
to zero - make any transition - between a succession of 1 bits. The method was
first used for communications signaling in which there was always a 1 bit at the
start of a character and thus there was a predictable and acceptable short
interval over which the sending and receiving devices had to maintain
synchronism independently.
Many variants of the basic principle have been derived to overcome
synchronization problems that occur at high speeds and long bit streams, one of
which is NRZI, nonreturn to zero inverted. (This should not be confused with
NRZ1, nonreturn to zero one (or mark)) NRZI is a form of
encoding used for magnetic recording in which a 1 bit is always indicated by a
magnetic flux transition, regardless of direction. Zeros do not give rise to
transitions and thus a long sequence of zeros could exceed the capability to
maintain synchronism. For this reason it cannot be used in single bit stream
recording such as that used on a disk, but can be used in multitrack systems
such as magnetic tape provided that choice of parity ensures that there is at
least one transition per character and the skew between tracks is small compared
to the pitch of transitions. See also disk format.
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