Baudot code

Baudot code is an early character encoding for telegraphy invented by French engineer Émile Baudot. It was the first widely adopted binary code for text communication, representing characters as combinations of five bits. The system was a foundational step in the evolution from Morse code to modern digital communication standards.

History and development

The code was developed by Émile Baudot, a former French Post Office employee, who patented his printing telegraph system in 1874. His work built upon earlier telegraph systems like the Hughes telegraph and aimed to automate telegraphy to increase speed and reduce errors compared to manual Morse code operation. The International Telegraph Union began standardizing telegraph codes in the late 19th century, leading to the formal adoption of a version of Baudot's system. A key improvement was introduced by Donald Murray, who rearranged the code to minimize wear on teleprinter mechanisms, creating the Murray code. This Murray variant was later standardized internationally as the International Telegraph Alphabet No. 2 (ITA2), which became the dominant teleprinter code for much of the 20th century.

Technical design

The system is a five-bit code, allowing for 32 possible combinations. To overcome this limitation and represent more than 32 characters, it employs two shift codes: the "letters" shift and the "figures" shift. These function like a mechanical shift key, toggling the interpretation of subsequent codes between two separate character sets. A typical teleprinter using the code would transmit a continuous stream of start and stop bits, synchronized by the machinery, though the code itself is purely a 5-bit representation. Operation required precise timing, managed by a distributor in Baudot's original multiplex system, which allowed multiple operators to share a single line. The physical transmission was typically via a neutral line telegraphy system using direct current pulses.

Character sets and variants

The original Baudot design had competing French and British versions with slightly different arrangements. The standardized ITA2 version, derived from the Murray code, included the Latin alphabet, digits, and a set of punctuation and control characters. Key control characters included carriage return, line feed, and the shift codes themselves. National variants emerged, such as the Russian Telegraph Alphabet for Cyrillic and a version for the Japanese language. The United States adopted a version often referred to as the Teletype Corporation code, used in devices like the Model 33 Teletype. For numeric data transmission, a more efficient variant called Fieldata was developed by the U.S. Army.

Operation and usage

Operators used a special five-key keyboard resembling a piano, pressing keys in chords to form each character's five-bit pattern. The system was central to news wire services like the Associated Press and Reuters, and to telex networks connecting businesses and government agencies globally. It saw extensive use in military communication, notably during World War II and the Cold War, and was the backbone of early data transmission for computer systems, such as those from IBM. Competitor systems included the American Standard Code for Information Interchange (ASCII), which eventually supplanted it due to its larger, more logical 7-bit design.

Impact and legacy

Baudot's invention was a critical bridge between alphabetic telegraphy and the digital age, directly influencing the design of later codes like ASCII and EBCDIC. The term baud, a unit of signaling rate, is derived from his name, though it measures symbol rate and not directly data rate. The code's last major commercial use was in Telex networks, which persisted into the 21st century in some regions. It holds a seminal place in the history of telecommunications, demonstrating the practical application of binary representation for text, a concept fundamental to all modern computing and digital communication.

Category:Character encoding Category:Telegraphy Category:French inventions