Teleprinters in Computing
Computers used teleprinters for input and output from the early days of computing. Punched card readers and fast printers replaced teleprinters for most purposes, but teleprinters continued to be used as interactive time-sharing terminals until video displays became widely available in the late 1970s.
Users typed commands after a prompt character was printed. Printing was unidirectional; if the user wanted to delete what had been typed, further characters were printed to indicate that previous text had been cancelled. When video displays first became available the user interface was initially exactly the same as for an electromechanical printer; expensive and scarce video terminals could be used interchangeably with teleprinters. This was the origin of the text terminal and the command line interface.
Paper tape was sometimes used to prepare input for the computer session off line and to capture computer output. The popular Teletype Model 33 used 7-bit ASCII code (with an eighth parity bit) instead of Baudot. The common modem communications settings, Start/Stop Bits and Parity, stem from the Teletype era.
In early operating systems such as Digital's RT-11, serial communication lines were often connected to teleprinters and were given device names starting with tt. This and similar conventions were adopted by many other operating systems. Unix and Unix-like operating systems use the prefix tty, for example /dev/tty13, or pty (for pseudo-tty), such as /dev/ptya0. In many computing contexts, "TTY" has become the name for any text terminal, such as an external console device, a user dialing in to the system on a modem on a serial port device, a printing or graphical computer terminal on a computer's serial port or the RS-232 port on a USB-to-RS-232 converter attached to a computer's USB port, or even a terminal emulator application in the window system using a pseudo terminal device.
Teleprinters were also used to record fault printout and other information in some TXE telephone exchanges.
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