Murray Code

The Baudot code, invented by Émile Baudot, is a character set predating EBCDIC and ASCII. It was the predecessor to the International Telegraph Alphabet No. 2 (ITA2), the teleprinter code in use until the advent of ASCII. Each character in the alphabet is represented by a series of five bits, sent over a communication channel such as a telegraph wire or a radio signal. The symbol rate measurement is known as baud, and is derived from the same name.

Technically, five-bit codes began in the 16th century, when Francis Bacon developed the cipher now called Bacon's cipher. The cipher was not designed for machine telecommunications (it was instead a method of encrypting a hidden message into another) and, although in theory it could be adapted to that purpose, it only covered 24 of the 26 letters of the English alphabet (two sets of letters, I/J and U/V, were expressed with the same code) and contained no punctuation, spaces, numbers or control characters, rendering it of little use.

Baudot invented his original code in 1870 and patented it in 1874. It was a 5-bit code, with equal on and off intervals, which allowed for transmission of the Roman alphabet, and included punctuation and control signals. It was based on an earlier code developed by Carl Friedrich Gauss and Wilhelm Weber in 1834. It was a Gray code (when vowels and consonants are sorted in their alphabetical order), nonetheless, the code by itself was not patented (only the machine) because French patent law does not allow concepts to be patented.

Baudot's original code was adapted to be sent from a manual keyboard, and no teleprinter equipment was ever constructed that used it in its original form. The code was entered on a keyboard which had just five piano-type keys and was operated using two fingers of the left hand and three fingers of the right hand. Once the keys had been pressed, they were locked down until mechanical contacts in a distributor unit passed over the sector connected to that particular keyboard, when the keyboard was unlocked ready for the next character to be entered, with an audible click (known as the "cadence signal") to warn the operator. Operators had to maintain a steady rhythm, and the usual speed of operation was 30 words per minute.

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