The D2 computer terminal is a cathode ray tube (CRT) designed for use with Data General mini-computers. Referred to as a dumb terminal or computer monitor, it is an interface device between people and computers in which communication is achieved by typed command lines which appear on a screen, with one line of text exchanged at a time.
The D2 is a descendant of the mechanical teletype (TTY), a device with a keyboard and printer that first appeared in the 1950s. The TTY was originally used in telecommunications where messages (telegrams) were digitised and sent to other remote TTYs. The mechanical TTY interface was eventually replaced by machines which used a screen to display text messages as they were exchanged.
The D2′s design enables the rotation and pitching of the screen housing over a wide field through central axis points both vertical and horizontal. This type of design facilitates effortless adjustment.
CRTs offered many advantages over previous technologies. They did not use paper and ink and made less noise. They also permitted the editing of instructions on screen as the cursor could be repositioned to any part of the screen to erase and change information. Multiple fonts, colour and graphics were also available.