Telegraph code
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A telegraph code is a character encoding used to transmit information through telegraphy machines. The most famous such code is Morse code.
Manual telegraph codes
Morse code can be transmitted and received with very primitive equipment. It encodes each letter of the alphabet as a series of dots and dashes.
Morse code has even been used to transmit Chinese characters. There already existed dictionaries which numbered the Chinese characters. It is simply a case of sending the numbers by Morse Code, and these numbers are then looked up in the dictionary at the receiving end.
In practice, this was a slow process, unless done by an expert Chinese telegrapher who could remember the numbers of the all the 5,000 odd characters which are in common use.
Automatic telegraph codes
Manufacturers developed teleprinters to allow typed messages to be transmitted and received without Morse code training. At the time, hardware costs depended on the length of the longest code. With an alphabet of 26 uppercase letters, the code had to be at least 5 bits long. To reduce hardware cost, teleprinter manufacturers adopted the fixed-length 5 bit Baudot code (rather than trying to use variable-length Morse code).
Users were not satisfied with the limited character set available in Baudot code. Demand for lowercase letters and more punctuation marks led to teleprinters with 7 bit ASCII code.
(Demand for accented vowels led to the 8 bit ISO 8859-1. Demand for Cyrillic, Hebrew, Arabic, Greek, and other letters led to many variations of ISO 8859. Demand for using more than one of these sets of letters at the same time led to the 16 bit Unicode. Demand for Chinese characters led to 20 bit Unicode, which clearly is impossible for any typewriter like formed character mechanical teleprinter, although dot-matrix printers can print Chinese characters.)
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