VDTs

VDTs, or video display terminals, are input-output devices that provide a text-oriented interface to a computer. A typical VDT combines a CRT or other display with a keyboard, connected to a host computer. Processing power resides mostly in the host; the terminal itself functions as a display and input conduit, rendering characters and relaying keyboard input based on a simple communication protocol. Early VDTs used character generation within the terminal to draw text, while later models supported more complex control sequences for cursor movement, screen clear, and simple line-drawing.

VDTs were central to interactive computing from the 1960s through the 1990s, especially in mainframe and minicomputer environments. They used serial or network connections and communicated using standardized protocols (for example VT100/VT220 family, ANSI escape sequences, and TN3270 for IBM mainframes). Popular models included DEC’s VT100 series, Wyse and Wyse-compatible terminals, HP, IBM 3270 family, and others.

In operation, the user types on the keyboard, sending commands to the host to be interpreted; the host returns screen updates. Because most processing was on the host, VDTs are often described as “dumb terminals” or lightly intelligent terminals, depending on the model.

With the rise of personal computers, graphical workstations, and networked thin clients, dedicated VDTs became less common in general use. Today, their legacy persists in terminal emulation software and remote access tools that provide a VDT-like interface on standard computing devices, and in legacy systems still operated in some industries where reliability and stability are prioritized.