VT220
| Company type | Product line |
|---|---|
| Industry | Computer terminals |
| Predecessor | VT100 |
| Founded | November 1983 |
| Products | VT220, VT240, VT241 terminals |
| Owner | Digital Equipment Corporation |
The VT200 series represents a lineup of computer terminals introduced by Digital Equipment Corporation (DEC) in November 1983. The entry-level VT220 model provided text-only functionality with support for multiple languages. Enhancing this, the VT240 incorporated monochrome ReGIS vector graphics, while the VT241 model offered color graphic capabilities. Serving as the successor to the widely used VT100, the VT200 series brought improved features housed within a more compact and lighter chassis, complemented by a reduced-size keyboard. It accommodated an extensive subset of ANSI X3.64 standards, including expanded international character sets and customizable glyph definitions.
This series enjoyed considerable commercial success. Originally priced at $1,295 and later lowered to $795, the VT220 combined competitive pricing, advanced features, and an appealing design that outperformed rivals of the period. By 1986, DEC had shipped approximately 165,000 units, securing a 42% share of the market—double that of its nearest competitor, Wyse. To counter emerging lower-cost alternatives, DEC launched the more budget-friendly $545 VT300 series in 1987. By this point, sales of the VT220 had surpassed one million units.
Hardware
Building upon the VT100 series foundation, the VT220 introduced a redesigned keyboard layout, a more compact enclosure, and utilized a faster Intel 8051 microcontroller. The terminals featured CRT displays available with white, green, or amber phosphor options.
In contrast to the bulkier designs of the VT100 and VT50 lines, the VT200 models integrated contemporary 1980s electronics closely around the CRT within a compact pyramidal housing, facilitating easier placement on work surfaces. The screen was positioned at roughly a 15-degree upward tilt for improved ergonomics and included an adjustable rear handle to modify viewing angles.
The included LK201 keyboard—developed at DEC's Roxbury facility—was among the first full-sized yet low-profile keyboards available. It was both lighter and smaller than earlier models and connected through a flexible coiled cable terminating in a telephone-style jack.
Connectivity options on VT200 terminals included both a 20mA current loop serial interface (via an 8-pin Molex-style connector) and a conventional 25-pin D-sub connector supporting RS-232; however, only one interface could be active at any given time. Subsequent versions replaced these connectors with proprietary Modified Modular Jack (MMJ) ports.
The VT240 model incorporated DEC's proprietary DEC T-11, a single-chip microcontroller derived from the PDP-11 minicomputer architecture. The color-capable VT241 combined the base VT240 unit with a VR-241 color monitor; existing VT240 owners could upgrade by swapping out their monochrome display and cable for these components.
Software
Designed for backward compatibility with the VT100, the VT220 introduced enhancements aimed at international users through support for multiple selectable character sets via ANSI commands.
Each character was rendered within a 10x10 pixel matrix, with ROM housing 288 glyphs comprising 96 printable ASCII characters, 67 control characters for display functions, 32 DEC-specific graphic symbols, and a reversed question mark to represent undefined characters.
To overcome limitations imposed by typical 7-bit communication links—offering only 96 printable characters—DEC implemented the National Replacement Character Set (NRCS). This system allowed selective substitution of individual glyphs within the base set; for example, replacing the US hash symbol (#) with the British pound sign (£). Fourteen such replacement sets were created to reduce the necessity for multiple terminal variants or extensive ROM capacity.
Additionally, the VT200 series supported a downloadable 96-character Dynamically Redefined Character Set (DRCS), which host systems could send to redefine glyphs dynamically. These custom characters were transmitted using encoded six-pixel vertical slices known as sixels, enabling flexible character graphics. This sixel methodology was later extended to support bitmapped graphics in following terminal models.
Escape Key Debate
Prior to the introduction of the VT220, the Escape key was commonly positioned in the upper left corner of keyboards. However, the VT220 shifted this key to the location typically reserved for the F11 key, situated near the center of the top row. This repositioning caused difficulties for users of the TECO editor, where frequent use of the Escape key is essential.
Legacy
Throughout the 1983–1984 development period of IBM's Model M keyboard, the VT220 was regarded as a leading design. IBM's design team decided to replicate the LK201 layout from the VT220, incorporating features such as the inverted-T arrangement for arrow keys, navigation keys placed above them, and a numeric keypad on the right side. The widespread adoption of the IBM PC helped establish the Model M layout as a standard recognized by ANSI and ISO, resulting in keyboard designs inspired by the VT220 layout becoming predominant.
See also
- ANSI escape code
- Rainbow 100
- Vttest - Utility for testing VT100 / VT220 / XTerm