A teletypewriter (TTY) is an input device that allows alphanumeric character to be typed in and sent, usually one at a time as they are typed, to a computer or a printer. The Teletype Corporation developed the teletypewriter, which was an early interface to computers. Teletype mode is the capability of a keyboard, computer, application, printer, display, or modem to handle teletypewriter input and output. Basically, this is a one-character-at-a-time mode of sending, receiving, or handling data, although it is often modified to handle a line of characters at a time. Since this mode requires little programming logic, it is often used where memory is limited. The Basic Input/Output Operating System ( BIOS ) sends messages to a PC display using teletype mode. Most printers offer a teletype mode. The simplest video display output format is text in teletype mode. Many modems today continue to include support for a TTY interface.