teletypewriters

Teletypewriter, commonly abbreviated as TTY, is an electromechanical device that can both transmit and print text messages. It combines a keyboard, a printer, and signaling hardware to send typed messages over long-distance networks, originally through telephone lines or telegraph circuits. Early teletypewriters often used punched paper tape as a persistent input/output medium, with later models accepting direct keyboard input and printing on standard paper.

Operation relied on telecommunication codes, most notably the Baudot code (ITA2), a five-bit system with separate letter and figure shifts. Over time, machines moved toward ASCII and more flexible signaling methods. Transmission speeds were modest by modern standards, typically measured in tens to a hundred baud, depending on the model and line quality.

Industrial and commercial use grew in the mid-20th century. Teletype Corporation and its successors produced a family of machines, including widely known models such as the Model 15, Model 28, Model 33, and Model 35. These devices served newsrooms, government offices, banks, and laboratories, linking distant locations via teleprinter networks such as Telex. Teletype machines also functioned as early computer terminals, providing a human-friendly interface for data entry and program output.

With the rise of electronic terminals, digital networks, and personal computers, traditional teletypewriters were gradually displaced from primary office use. In contemporary terms, the acronym TTY is often associated with telecommunications devices for the deaf (TTY or TDD), which enable text communication over telephone networks using keyboards and displays, typically with a modem or network adapter. This modern usage differs from historical teletypewriter networks but shares the common idea of text-based electronic communication.