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Baudot developed his first multiplexed telegraph in 1872 [2] [3] and patented it in 1874. [3] [4] In 1876, he changed from a six-bit code to a five-bit code, [3] as suggested by Carl Friedrich Gauss and Wilhelm Weber in 1834, [2] [5] with equal on and off intervals, which allowed for transmission of the Roman alphabet, and included punctuation and control signals.
Baudot invented his telegraph code in 1870 [3] and patented it in 1874. [4] It was a 5-bit code, with equal on and off intervals, which allowed telegraph transmission of the Roman alphabet, punctuation and control signals. By 1874 or 1875 (various sources give both dates) he had also perfected the electromechanical hardware to transmit his code.
The Baudot code was a 5-bit binary code, with the bits sent serially. Having a fixed length code greatly simplified the machine design. The operator entered the code from a small 5-key piano keyboard, each key corresponding to one bit of the code.
Baudot code / ITA1: 1870 5 bits Piano-like telegraph operation, SIGCUM cipher operation Chinese telegraph code: 1881 4 digits Chinese telegraph communications Murray code: 1901 5 bits Machine run telegraph operation using punched paper, moved optimization from minimal operator fatigue to minimal machinery wear ITA2: 1924 [1] 5 bits
Tape for punching was usually 0.00394 inches (0.100 mm) thick. The two most common widths were 11 ⁄ 16 inch (17 mm) for five bit codes, and 1 inch (25 mm) for tapes with six or more bits. Hole spacing was 0.1 inches (2.5 mm) in both directions. Data holes were 0.072 inches (1.8 mm) in diameter; sprocket feed holes were 0.046 inches (1.2 mm). [8]
Early teletypewriters used the ITA-1 Baudot code, a five-bit code. This yielded only thirty-two codes, so it was over-defined into two "shifts", "letters" and "figures". An explicit, unshared shift code prefaced each set of letters and figures. In 1901, Baudot's code was modified by Donald Murray.
Donald Murray (20 September 1865– 14 July 1945) was an electrical engineer and the inventor of a telegraphic typewriter system using an extended Baudot code that was a direct ancestor of the teleprinter (teletype machine).
A companion Teletype Model 32 used the older, established five-bit Baudot code. [5] Because of its low price and ASCII compatibility, the Model 33 was widely used with early minicomputers, and the large quantity of the teleprinter sold strongly influenced several de facto standards that developed during the 1960s and 1970s. [6]