The VT100 was a video display terminal manufactured by Digital Equipment Corporation, introduced in 1978. It consisted of a keyboard and a cathode-ray-tube screen connected to a host computer over a serial line, and it displayed text in a grid of characters, typically 80 columns by 24 rows. Unlike the printing teletypes it succeeded, the VT100 could address and update any position on the screen, making it suitable for full-screen interactive programs such as text editors.
What made the VT100 historically decisive was its command set. The VT100 User Guide (EK-VT100-UG-003, Digital Equipment Corporation, third edition June 1981) documents the escape and control sequences the terminal recognized for cursor positioning, scrolling regions, character attributes, and screen erasure. Crucially, these sequences implemented the control-function framework of ANSI X3.64, the standard equivalent to ECMA-48 and ISO/IEC 6429. Earlier DEC terminals had used private, incompatible control codes; the VT100 deliberately adopted the emerging ANSI standard, which meant programs written to drive it spoke a documented, vendor-neutral vocabulary.
Because the VT100 was widely deployed and its sequences were standards-based, software was written assuming a VT100, and “VT100 compatible” became a baseline claim for other manufacturers’ terminals. The terminal capability databases that Unix systems use to abstract over terminal differences, termcap and later terminfo, carry a vt100 entry that countless later terminals and emulators present as their type through the TERM environment variable. In practice the VT100 set the reference behavior that the entire ecosystem standardized around.
The VT100 also introduced features that became expected of serious terminals, including selectable 80- or 132-column display, smooth scrolling, double-height and double-width characters, and a programmable set of character attributes. The User Guide describes these along with the setup mode that let an operator configure the terminal interactively, a notable convenience compared with the hardware switches of earlier models.
The VT100’s lasting legacy is emulation. Every modern terminal emulator, from xterm to the terminal windows built into graphical desktops, parses and acts on the VT100’s escape sequences so that decades of software continues to run unchanged. When a program today moves the cursor or sets a color, it is, in effect, talking to a 1978 DEC terminal that exists only as software. The VT100 is therefore less a piece of obsolete hardware than the permanent specification that text-mode computing settled on.