TTY

TTY stands for teletypewriter. Historically, a TTY was an electromechanical device that printed characters on paper or tape and could be linked to telephone lines to transmit messages. Teletype machines were widely used in newsrooms, business, and government during the mid-20th century. As computing emerged, the term TTY came to describe the interface that allows a user to interact with a computer via text.

In modern computing, a TTY can be a physical terminal or a software abstraction that provides text input and output. In Unix-like systems, TTYs are represented by device files such as /dev/tty for the controlling terminal, /dev/ttyS0 for a serial port, and /dev/pts/N for pseudo-terminals used by terminal emulators and remote sessions. The concept includes the controlling terminal of a process and the mechanisms that manage input and output, including login prompts started by a getty on a TTY.

Terminal emulators like xterm or GNOME Terminal provide virtual or pseudo-terminals, enabling graphical environments to interact with shells. Remote access tools such as SSH also rely on pseudo-terminals to emulate a local terminal for the remote command line.

TTY devices employ line discipline and termios settings, controlling input modes, buffering, and character processing. The simple command tty prints the file name of the terminal connected to standard input.

In accessibility, the term TTY (or TDD) refers to devices that support text communication over telephone networks for people who are deaf or hard of hearing, often using specialized adapters or IP-based technologies.