A TTY may refer to any of the following:
1. Short for TeleTYpewriter or TeleTYpe, TTY is an electronic typewriter or teleprinter that has a keyboard and a printer. Each time a key is pressed, it would be printed to paper like a typewriter. Later, modern TTY machines also print to a screen. Teleprinters were widely used in the late 1800's and early 1900's and today have been replaced by computers with keyboards.
Teletype machines were available in three different modes shown below.
- Automatic Send and Receive (ASR) -- Able to send and receive.
- Receive Only (RO) -- only capable of receiving data and not sending.
- Keyboard Send and Receive (KSR) -- TTY with keyboard capable of sending and receiving data.
2. Today, TTY is used to describe a terminal session or line. Users who are using Linux may view a process or which users are logged in by typing a tty, such as ttyx, where x is any numerical value. For example, tty1, tty2, tty3, tty4, tty5, tty6, tty7, and so on.