The VT420 was an ANSI standard computer terminal introduced in 1990 by Digital Equipment Corporation (DEC). The 420 was the only model in the 400 series, replacing the VT320. There were no color or graphics-capable 400 series terminals; the VT340 remained in production for those requiring ReGIS and Sixel graphics and color support. The entire lineup of VT300s and VT420 was eventually replaced by the relatively unknown VT500 series starting in 1993.
ANSI escape sequences are a standard for in-band signaling to control the cursor location, color, and other options on video text terminals and terminal emulators. Certain sequences of bytes, most starting with Esc and '[', are embedded into the text, which the terminal looks for and interprets as commands, not as character codes.
A computer terminal is an electronic or electromechanical hardware device that is used for entering data into, and displaying or printing data from, a computer or a computing system. The teletype was an example of an early day hardcopy terminal, and predated the use of a computer screen by decades.
Digital Equipment Corporation (DEC), using the trademark Digital, was a major American company in the computer industry from the 1950s to the 1990s.
The VT420 was essentially an updated VT320, adding the multi-session capabilities originally introduced on the VT330 and VT340.
Those two models had included a system known as TD/SMPwhich allowed two sessions to be multiplexed over a single serial connection to a compatible terminal server. Alternately, the two sessions could be supported by separate serial connections on those models with multiple MMJ ports. Using either method, the VT330/340/420 could either show the two sessions behind each other, using a key sequence to flip back and forth, or split the screen horizontally to display the sessions one above the other, or vertically side-by-side.
TD/SMP, short for Terminal Device/Session Management Protocol, was a terminal multiplexer system introduced by DEC on their VT330/340 terminals in 1987. The terminal-side was referred to as SSU. TD/SMP allowed data from two separate host sessions to be sent to a compatible computer terminal over a single serial port. The format was patented and never described in depth, limiting it to DEC's own terminal servers and terminals.
A terminal server enables organizations to connect devices with an RS-232, RS-422 or RS-485 serial interface to a local area network (LAN). Products marketed as terminal servers can be very simple devices that do not offer any security functionality, such as data encryption and user authentication. The primary application scenario is to enable serial devices to access network server applications, or vice versa, where security of the data on the LAN is not generally an issue. There are also many terminal servers on the market that have highly advanced security functionality to ensure that only qualified personnel can access various servers and that any data that is transmitted across the LAN, or over the Internet, is encrypted. Usually companies which need a terminal server with these advanced functions want to remotely control, monitor, diagnose and troubleshoot equipment over a telecommunications network.
The Modified Modular Jack (MMJ) is a small form-factor serial port connector developed by Digital Equipment Corporation (DEC). It uses a modified version of the 6P6C modular connector with the latch displaced off-center so standard modular connectors found on Ethernet cables or phone jacks cannot accidentally be plugged in. MMJ connections are used on Digital minicomputers, such as the PDP-11, VAX and Alpha systems, and to connect terminals, printers, and serial console servers.
The VT420 also added a number of more minor features. One was to add a number of PC character sets, allowing the terminal to be used with a variety of PC programs. Another allowed the terminal to generate the proper character sequences to produce rectangular-area commands. For instance, one could select a rectangular area and fill it with a particular character, or blank it out. This was in addition to the terminal-side editing system introduced on the VT300s.
The VT420 had a total of 5 sets of 94 characters for normal VT operation, another 3 sets of 128 PC characters, and 1 set of 96 characters containing various graphics and math symbols. Like all models since the VT200 series, the user could also upload a custom character set of their own design using the Sixel system. Likewise, it also supported the National Replacement Character Set system, which swapped out single characters in 7-bit modes to allow basic changes like swapping the # for the £ for use on UK systems.
The VT220 is an ANSI standard computer terminal introduced by Digital Equipment Corporation (DEC) in 1983. The VT240 added monochrome ReGIS vector graphics support to the base model, while the VT241 did the same in color. The 200 series replaced the successful VT100 series, providing more functionality in a much smaller unit with a much smaller and lighter keyboard. Among its major upgrades was a number of international character sets, as well as the ability to define new character sets.
Sixel, short for "six pixels", is a bitmap graphics format supported by terminals and printers from DEC. It consists of a pattern six pixels high and one wide, resulting in 64 possible patterns. Each possible pattern is assigned an ASCII character, making the sixels easy to transmit on 7-bit serial links.
The National Replacement Character Set, or NRCS for short, was a feature supported by later models of Digital's (DEC) computer terminal systems, starting with the VT200 series in 1983. NRCS allowed individual characters from one character set to be replaced by one from another set, allowing the construction of different character sets on the fly. It was used to customize the character set to different local languages, without having to change the terminal's ROM for different counties, or alternately, include many different sets in a larger ROM. Many 3rd party terminals and terminal emulators supporting VT200 codes also supported NRCS.
All DEC terminals that came after the VT100, including the VT420, are able to emulate their ancestors. The VT420 had VT100 and VT52 emulating modes.
The VT100 is a video terminal, introduced in August 1978 by Digital Equipment Corporation (DEC). It was one of the first terminals to support ANSI escape codes for cursor control and other tasks, and added a number of extended codes for special features like controlling the status lights on the keyboard. This led to rapid uptake of the ANSI standard, becoming the de facto standard for terminal emulators.
The VT50 was a CRT-based computer terminal introduced by Digital Equipment Corporation (DEC) in July 1974. It provided a display with 12 rows and 80 columns of upper-case text, and used an expanded set of control characters and forward-only scrolling based on the earlier VT05. DEC documentation of the era refers to the terminals as the DECscope, a name that was otherwise almost never seen.
The screen itself was a 14" flat CRT with a resolution of 800 (horizontal) by 400 (vertical) pixels. A variety of glyphs were available that provided 80 or 132 characters across, and 24, 36 or 48 lines of text vertically. The screen had room for 25 lines at normal font sizes, but the last line was normally used for status indications, like ⇪ Caps Lock. The MMJ ports could operate at speeds up to 38,400 bit/s, double that of the VT300s maximum 19,200 bit/s.
The PDP-11 is a series of 16-bit minicomputers sold by Digital Equipment Corporation (DEC) from 1970 into the 1990s, one of a succession of products in the PDP series. In total, around 600,000 PDP-11s of all models were sold, making it one of DEC's most successful product lines. The PDP-11 is considered by some experts to be the most popular minicomputer ever.
RT-11 is a discontinued small, single-user real-time operating system for the Digital Equipment Corporation PDP-11 family of 16-bit computers. RT-11 was first implemented in 1970 and was widely used for real-time systems, process control, and data acquisition across the full line of PDP-11 computers.
Text mode is a computer display mode in which content is internally represented on a computer screen in terms of characters rather than individual pixels. Typically, the screen consists of a uniform rectangular grid of character cells, each of which contains one of the characters of a character set. Text mode is contrasted to all points addressable (APA) mode or other kinds of computer graphics modes.
The Tektronix 4010 series was a family of text-and-graphics computer terminals based on storage-tube technology created by Tektronix. Several members of the family were introduced during the 1970s, the best known being the 11-inch 4010 and 19-inch 4014, along with the less popular 25-inch 4016. They were widely used in the computer-aided design market in the 1970s and early 1980s.
The HP 2640A and other HP 264X models were block-mode "smart" and intelligent ASCII standard serial terminals produced by Hewlett-Packard using the Intel 8008 and 8080 microprocessors.
The Rainbow 100 was a microcomputer introduced by Digital Equipment Corporation (DEC) in 1982. This desktop unit had a monitor similar to the VT220 in a dual-CPU box with both 4 MHz Zilog Z80 and 4.81 MHz Intel 8088 CPUs. The Rainbow 100 was a triple-use machine: VT100 mode, 8-bit CP/M mode, and 16-bit CP/M-86 or MS-DOS mode using the 8088.
The VT520 is an ANSI standard computer terminal introduced by Digital Equipment Corporation (DEC) in 1993 and 1994. The VT520 is multi-session monochrome text terminal. The VT525 added color support, while the VT510 was a single-session, text-only version with a built-in monitor. The VT525 appears to be the most popular model in the series.
ReGIS, short for Remote Graphic Instruction Set, was a vector graphics markup language developed by Digital Equipment Corporation (DEC) for later models of their famous VT series of computer terminals. ReGIS supported rudimentary vector graphics consisting of lines, circular arcs, and similar shapes. Terminals supporting ReGIS generally allowed graphics and text to be mixed on-screen, which made construction of graphs and charts relatively easy.
The Linux console is a system console internal to the Linux kernel. The Linux console provides a way for the kernel and other processes to send text output to the user, and to receive text input from the user. The user typically enters text with a computer keyboard and reads the output text on a computer monitor. The Linux kernel supports virtual consoles - consoles that are logically separate, but which access the same physical keyboard and display. The Linux console are implemented by the VT subsystem of the Linux kernel, and do not rely on any user space software. This is in contrast to a terminal emulator, which is a user space process that emulates a terminal, and is typically used in a graphical display environment.
Text-based semigraphics or pseudographics is a primitive method used in early text mode video hardware to emulate raster graphics without having to implement the logic for such a display mode.
The VT320 was an ANSI standard computer terminal introduced by Digital Equipment Corporation (DEC) in 1987. The VT320 was the text-only version, while the VT330 added monochrome ReGIS, Sixel and Tektronix 4010 graphics, and the VT340 added color.
Waveform graphics was a simple vector graphics system introduced by Digital Equipment Corporation (DEC) on the VT55 and VT105 terminals in the mid-1970s. It was used to produce graphics output from mainframes and minicomputers. DEC used the term "waveform graphics" to refer specifically to the hardware, but it was used more generally to describe the whole system.
The VT1000 was a monochrome X Window System computer terminal introduced by Digital Equipment Corporation (DEC) in April 1990. The VT1200 replaced the VT1000 later that year, consisting of a code update and a bump in the RAM from 1 to 2 MB. All of the VT1000 series communicated with their host computers over Ethernet, supporting TCP/IP as well as DEC's terminal-oriented Local Area Transport (LAT) protocol. They also included standard serial ports to allow basic terminal emulation, built into the ROM.
DEC Special Graphics is a 7-bit character set developed by Digital Equipment Corporation. This was used very often to draw boxes on the VT100 video terminal and the many emulators, and used by bulletin board software. The escape sequence
Esc ( 0 switched the codes for lower-case ASCII letters to draw this set, and the sequence
Esc ( B switched back.