VT220

VT220
Name	VT220
Developer	Digital Equipment Corporation
Type	Video terminal
Release	1983
Discontinued	1990s
Media	Serial line
Cpu	Intel 8086 (controller)
Display	80×24 text
Connectivity	RS-232, DECnet (optional)

VT220

The VT220 was a widely used text terminal developed by Digital Equipment Corporation for use with VAX, PDP-11, and other minicomputer systems; it succeeded earlier models such as the VT100 and preceded later terminals like the DEC VT320. The device became a standard in laboratories, universities, and enterprises that employed Berkeley Software Distribution UNIX hosts, DECnet networks, and serial console servers from vendors such as Xylogics and Hewlett-Packard. Its adoption influenced terminal emulation standards in software projects including xterm, PuTTY, and GNU Screen.

History

DEC introduced the VT220 in 1983 as part of the company's VT200 series, following the commercial success of the VT100 family and contemporary with the advent of TCP/IP adoption on campus networks and the expansion of Internet backbones. The terminal's release coincided with the proliferation of ANSI X3.64 and de facto control sequences used by operating systems like SunOS, Ultrix, and 4.3BSD. DEC marketed the VT220 to institutions running VAX/VMS and RSX-11 as well as to sites using Digital Equipment Corporation's own network protocols. Competition included terminals from Wyse, Tektronix, and Honeywell, and the VT220 helped shape standards adopted by terminal emulators in projects such as ncurses and termcap.

Design and Features

The VT220 featured a compact enclosure and detachable keyboard modelled after DEC's LK201 layout, influencing later keyboards used by IBM PC clones and workstation manufacturers like Sun Microsystems. It supported 80×24 and 132×24 display modes for compatibility with applications from Oracle Corporation database consoles, Emacs editors running on BSD systems, and terminal-based mail clients like Pine. The terminal implemented ANSI escape sequences from ISO/IEC 6429 and DEC-specific controls, enabling features used by editors such as vi and utilities like ed. Optional modules provided support for 220–240 V power systems used in European Economic Community installations and character sets for languages used in United Kingdom, France, and Germany locales.

Technical Specifications

The VT220 used a microprocessor-based controller and supported serial communication over RS-232 with baud rates up to 19,200 or higher with options, interfacing with terminal servers from Cisco Systems and modem stacks from Hayes Microcomputer Products. It offered selectable character sets including ASCII, DEC Multinational Character Set, and National Replacement Character Set variants used in ISO 646 implementations. The CRT displayed monochrome phosphorus screens alongside adjustable intensity and cursor styles familiar to operators of X Window System terminals; power consumption and thermal design followed industrial practices of the early 1980s. Firmware supported keyboard compose sequences and programmable function keys utilized by applications such as Lotus 1-2-3 ports and COBOL-based transaction systems.

Emulation and Compatibility

Because of its widespread use, the VT220 became a reference model for terminal emulators in software like xterm, PuTTY, Tera Term, and libraries such as ncurses and termcap/terminfo. Compatibility layers ensured proper handling of DEC private mode sequences used by text editors vi and emacs on hosts including SunOS, HP-UX, AIX, and SCO UNIX. Emulators also addressed differences between VT220 controls and those of successors like the VT320 or video terminals from Tektronix that supported graphics protocols such as ReGIS. Terminal multiplexers such as screen and tmux preserved behavior expected by legacy software interacting with the VT220 control set.

Models and Variants

The VT200 series included the VT220 alongside sibling models like the VT100, VT102, and later VT320; DEC offered regional keyboard variants and factory options such as built-in serial converters and local language ROMs used for French and German locales. OEMs and aftermarket vendors produced upgraded housings and bracket kits for rackmounting in equipment racks common in Bell Labs and MIT research labs. Some variants incorporated additional firmware to support terminal server protocols and integration with DEC VAXcluster console arrangements.

Impact and Legacy

The VT220's control sequences, keyboard layout, and character-set support left a lasting imprint on terminal standards, influencing emulator behavior in Linux distributions, workstation terminals from Sun Microsystems, and SSH clients used by administrators at institutions such as NASA and Los Alamos National Laboratory. Its role in standardizing escape sequences helped unify cross-platform text-based software for environments running VMS, UNIX flavors, and early Microsoft networking products. Museums and collections such as the Computer History Museum preserve functioning units, reflecting the VT220's importance in the evolution of human–computer interaction and terminal-centric computing.

Category:Computer terminals