What Is Teleprinting?

Teleprinting is the technology of transmitting text messages electrically between distant locations and reproducing them in printed form at the receiving end. A teleprinter combines a keyboard with a printing mechanism: keystrokes generate coded electrical pulses, which travel over wire or radio circuits to a receiving machine that decodes and prints the corresponding characters. The technology emerged in the late nineteenth century as an extension of telegraphy, removing the need for skilled Morse code operators by allowing trained typists to compose and receive messages directly. As described in Encyclopaedia Britannica, teleprinters became central to business and government communications from the 1920s until computer terminals and fax machines supplanted them in the 1980s.

Teleprinting draws from electrical engineering, mechanical design, and coding theory. Its evolution traces the shift from analog electrical signaling to structured character encodings, and ultimately to fully digital communications networks.

Teleprinter Machines and the Start-Stop Protocol

Early teleprinters operated on a synchronous basis, requiring sender and receiver to run at exactly matched speeds, which was mechanically demanding. The start-stop approach, adopted widely by the 1920s, solved this by framing each character transmission with a start pulse and one or more stop pulses. The receiver's mechanism was engaged by the start pulse, clocked through the data bits, then held in the rest position by the stop pulse until the next character arrived. This design, pioneered by Charles Krum and adopted by the Teletype Corporation's 1924 series, allowed teleprinters to be built with ordinary synchronous motors rather than requiring precision clock synchronization over long distances. The Teletype Model 15 became a standard in the United States, and similar machines were produced by Siemens in Germany and other manufacturers globally.

Character Encoding and the Baudot Code

The dominant character code for teleprinting through most of the twentieth century was the five-bit code developed by Emile Baudot in France during the 1870s and later revised as the International Telegraph Alphabet No. 2 (ITA2). Five binary signals yield 32 combinations, which were extended to cover uppercase letters, numerals, and punctuation by using two shift states. The term "baud," the unit of symbol rate in telecommunications, derives from Baudot's name. As explained in Stanford's overview of the Baudot code, when digital computers arrived in the 1960s the seven-bit American Standard Code for Information Interchange (ASCII) replaced ITA2 in many applications, increasing the character set to 128 and raising practical transmission speeds from roughly 75 words per minute on Baudot machines to approximately 150 words per minute on ASCII-capable units.

Telex Networks and the Transition to Digital Communication

The global Telex network, established from the late 1920s onward, extended teleprinting from point-to-point leased lines to a switched network analogous to the telephone system. Subscribers dialed destinations using a rotary answerback system, and the network routed the connection. At its peak in the 1970s and 1980s, Telex served banks, news agencies, shipping companies, and government ministries as the primary medium for international text communication. The diversity of printing telegraph codes and their relationship to transmission technology illustrates how encoding choices were shaped by the mechanical and electrical constraints of each generation of equipment. Digital data networks, X.25 packet switching, and ultimately the internet rendered dedicated teleprinting infrastructure obsolete, though the underlying ideas of structured asynchronous character transmission carried directly into serial communications interfaces such as RS-232.

Applications

Teleprinting has applications in a wide range of disciplines, including:

• News wire services and press agency distribution
• Financial market data and commodity price reporting
• Diplomatic and military messaging
• Weather service data distribution
• Maritime and aviation operational communications