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VT220
Features from the DEC VT220 terminal (1983), which added insert/delete character operations (ICH, DCH), 8-bit control codes, user-defined keys, and national replacement character sets. The VT220's editing sequences (ICH, DCH, IL, DL) are fundamental to full-screen terminal applications — they allow inserting and deleting characters and lines without redrawing the entire screen. Modern terminals universally support VT220 editing operations. The VT220 shipped with DEC's iconic LK201 keyboard — the first to feature a dedicated editing keypad (Insert, Remove, Find, Select) that influenced PC keyboard layouts for decades. DEC sold over a million VT220 units, making it one of the most commercially successful terminals ever produced.
See also: DEC VT220 (historical terminal)
The VT220's key protocol contribution is character-level editing. Insert Character (ESC [n@ for ICH) and Delete Character (ESC [nP for DCH) shift existing text right or left without redrawing the entire line. Insert Line (ESC [nL) and Delete Line (ESC [nM) do the same vertically. These four sequences are what make vim's insert mode, tmux's pane resizing, and shell autocompletion feel responsive — without them, every edit requires repainting from the changed position to the end of screen.
The VT220 also introduced device attribute queries: DA1 (ESC [c) asks "what are you?" and DA2 (ESC [>c) asks for firmware version. Modern terminals still respond to these queries, and applications use them for feature detection — a terminal's DA1 response reveals what protocols it supports, enabling graceful degradation.
For developers building TUI applications, VT220 editing sequences are the difference between smooth, flicker-free updates and full-screen redraws. Libraries like ncurses use ICH/DCH/IL/DL extensively, and understanding them explains why some terminal updates feel instant while others flash.
Historical Context
The DEC VT220, released in November 1983, was DEC's most commercially successful terminal — over 1 million units shipped, commanding 42% market share in 1986. Priced at $1,295, it replaced the VT100 as the standard office terminal.
The VT220 introduced insert/delete operations (ICH, DCH, IL, DL) that are fundamental to every full-screen terminal application — vim, tmux, less all depend on these sequences. It also added 8-bit control codes, user-defined keys, and national replacement character sets.
The VT220's LK201 keyboard layout shaped every keyboard that followed. IBM's Model M design team explicitly copied the inverted-T arrow cluster, navigation keys, and numeric keypad arrangement. The VT220 also controversially moved the Escape key from the upper-left corner, sparking a debate that persists through Vim users today.
Analysis2026-04-06
Terminal Applications
| Feature | iTerm2 | Ghostty | VS Code | Warp | Cursor | Terminal.app |
|---|---|---|---|---|---|---|
| Delete characters (DCH) | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
| Insert characters (ICH) | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
| Secondary Device Attributes (DA2) | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
| Selective Erase (DECSED) | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |