Mark and space

Mark and space are terms used in telecommunications to describe two different signal states of a communications signal, generally at the physical layer of a communications system. The terms derive from the early days of the electric telegraph system, where the marking state would cause a mark to be output on paper, and the spacing state would create no mark.

The terms would continue to be used in systems such as RS-232, with similar conventions, that "mark" would be encoded by a negative voltage (or current flow), and "space" by a positive voltage (or no current flow).[1] In such systems, the line is typically left in the "mark" state when idle.[2]

"Mark" is generally identified with the binary digit "1" and "space" with the binary digit "0".[1]

References
  1. Freeman, Roger L. (2004-06-11). Telecommunication System Engineering. John Wiley & Sons. ISBN 978-0-471-45133-4.
  2. Martin, James; Martin, James Thomas; S.J, James Martin (1976). Telecommunications and the Computer. Prentice Hall Professional. ISBN 978-0-13-902494-8.

See also


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