Installing and Using the VT420 Video Terminal


Action field

Terminal features in set-up that make the VT420 perform an immediate action.

Active session

The session that you are currently using on the VT420. You use the F4 (Session) key to change the active session.

Application software

A program that performs a specific function for a particular class of computer users. Examples: spreadsheet applications, word processing applications, text editing applications.

Auto print mode

A method of printing information directly from the host system. The VT420 sends a display line to the printer after a carriage return or form feed character.

Bottom margin

The last line of the scrolling region.


Comite Consultatif International de Telegraphique et Telephonique (International Telegraph and Telephone Consultative Committee). A standards committee for the communication industry in Europe.

Character set

A group of graphic characters and control characters stored as a unit in the terminal. Graphic characters are characters you can display on the screen. Control characters perform special functions.

Compose character

A character produced when you press two or three keys in a certain sequence. You can use compose sequences to produce characters that do not appear as standard keys on your keyboard.

Current page

The page in page memory that the cursor is on.


An indicator that highlights the active position on the screen. The VT420 uses different cursor characters for text and set-up.

Data processing keys

Keys that have characters on the left half and right half of their keycap. The characters on the right half of the keycap are data processing characters. You must select a special set-up feature to use these characters.

Diacritical marks

Marks or symbols that indicate a change in the standard pronunciation of a letter. Examples of diacritics are the acute accent (┬┤), grave accent (`), and tilde (~).

On the VT420, you can use diacritical marks (if available on your keyboard) to start two-stroke compose sequences. When you press a key with a nonspacing diacritical mark, the cursor does not advance until you press the next key.


The information that appears on the screen.

Factory default

A standard setting for a feature. The VT420 uses factory-default settings, unless you select a new setting. Many set-up features have default settings.

Full-duplex modem

A modem that can handle simultaneous, two-way communications.

Host system

The computer system(s) you connect to the VT420. If you connect the terminal to two systems, one is the primary host and one is the secondary host.

Inactive session

A session that you are not currently using. You can run two sessions at the same time on the VT420, but you can only interact with one session at a time.

Keyboard indicator line

A status line with six fields that provide information about the keyboard's status. The keyboard indicator line appears at the bottom of the screen, in the smaller, 132-column font. See also status line.


Modulator - demodulator. A device that converts data from a computer or terminal into signals that can be sent over a telephone line.

Modifier key

A key pressed in combination with another key, to modify the code sent by that key. Ctrl is a modifier key.

National replacement character set

Seven-bit character sets for many European languages. Each character set with 94 characters. NRC sets are similar to the ASCII set, except for a few characters.

Nonspacing diacritical keys

See Diacritical marks.

Nonvolatile memory

Nonvolatile RAM (random access memory). The VT420 uses this memory to store the saved settings of set-up features. The settings are not lost when you turn the terminal off.


A section of the terminal's page memory. Each page has left, right, top and bottom margins. You can define the size and layout of a page by using the page arrangement feature.

Page arrangement

A set-up feature that divides page memory into one of four standard page sizes. The default setting of the page arrangement feature is 3 pages of 24 lines each (for two sessions) or 6 pages of 24 lines each (for a single session).

Page memory

Memory in the VT420 that can store the information you enter from the keyboard. The total size of page memory is 144 lines. Page memory is divided into pages. You can select from several standard page sizes. The amount of memory available depends on the page size selected and the number of sessions used (one or two).


Pointing a window to display different parts of page memory. Panning a window is similar to panning a camera. The window does not move on the screen; you point the window at another location in page memory.


Picture elements. The smallest displayable unit on a video screen. To display a character, the terminal turns on a series of pixels.


The logical route for data in or out of the controller board on the VT420. Also, another term for connector. One port can support one or more connectors. All the VT420 connectors are on the rear of the terminal.

Prefix key

A key that you press and release before pressing another key, to change the function of one or more keystrokes. Compose Character is a prefix key.


To restore communication with an interrupted session.

Saved settings

The settings of set-up features that the VT420 uses when you turn the terminal on. You can change these settings or use the factory-default settings.


Moving data between the margins of the page currently displayed. Data scrolled past the margins is lost from page memory, but usually not from the host system.

Scrolling region

The area on the current page that is between the top, bottom, left, and right page margins. The default scrolling region is the complete page. Only a programmer can change the page margins.


An active connection between the VT420 and a host system. When you log in to a computer from the terminal, you open a session.


A set of display screens on the VT420 that let you examine and change the settings of the terminal's operating features. You can use the keyboard to change settings.


Digital's Session Support Utility. This software lets you run two sessions over one communication line.

Status line

A display line that provides information about the session's current operating state. The status line appears at the bottom of the screen or at the bottom of the session (if you are running two sessions). The VT420's status display feature has three settings -- indicator, none, and host-writable. The VT420 always displays the status line for the current session in set-up.

Terminal server

An intelligent unit that can connect a number of asynchronous devices (terminals and printers) to a host system. For example, Digital's DECserver 200 can link eight VT420 terminals to a system in a local area network (LAN), using a high-speed Ethernet cable.

User-defined keys (UDKs)

Any of the 15 keys, F6 to F20, on the top row of the keyboard for which a user has defined special functions. You can use UDKs to store frequently used text and commands.

Visual character attribute

A quality of a display character that highlights the character, such as bolding and underlining.


A specified area of the screen used to display information from page memory. You can divide the screen horizontally into two windows, to display information from two sessions at the same time.