The encyclopedia · Software & IT · Technical decision · 1870–1932
Baudot's five-bit code made telegraphy a typewriter and ran for decades
Emile Baudot's 1870 five-bit code with FIGS/LTRS shifts let a keyboard send text; CCITT's ITA2 made it the world's teleprinter code until ASCII.
Emile Baudot · CCITT
the move
Morse code needed trained operators and produced variable-length symbols that machines could not easily print. Emile Baudot's 1870 code used fixed five-bit values, 32 codewords, so an operator could type characters with five keys and the telegraph could carry them mechanically.
The clever part was the shift trick: the same codewords represent letters in one mode and numbers and punctuation in another, switched by FIGS and LTRS codes. That let a 32-code alphabet carry a full character set and foreshadowed data compression, since most characters average under six bits.
Baudot's code became the basis of the CCITT's ITA2 standard in the 1930s, the dominant teleprinter code for more than 40 years, with a North American variant called USTTY. It persisted until seven-bit ASCII arrived in 1963, and his name survives in the unit 'baud'.
why it works
- Five bits fit 1930s electromechanical hardware and 45-bits-per-second lines.
- The shift mechanism expanded 32 codes into a full character set.
- ITA2 standardization made telegraph and teleprinter systems interoperable.
- Fixed-length codes are simpler to time and synchronize than variable-length Morse.
what transfers
When a channel is narrow, design the code around the medium: a compact, stateful encoding beats a rich one because it fits the hardware the market already owns.
what came after
ITA2 was the world's teleprinter standard until ASCII displaced it, and the five-key, shift-based idea carried into later character encodings; the baud unit still measures symbol rate.
references
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