The VT52 was a CRT

Cathode ray tube

The cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images. The image may represent electrical waveforms , pictures , radar targets and...

-based computer terminal

Computer terminal

A computer terminal is an electronic or electromechanical hardware device that is used for entering data into, and displaying data from, a computer or a computing system...

 produced by Digital Equipment Corporation

Digital Equipment Corporation

Digital Equipment Corporation was a major American company in the computer industry and a leading vendor of computer systems, software and peripherals from the 1960s to the 1990s...

 introduced in September, 1975 . It provided a screen of 24 rows and 80 columns of text and supported all 95 ASCII

ASCII

The American Standard Code for Information Interchange is a character-encoding scheme based on the ordering of the English alphabet. ASCII codes represent text in computers, communications equipment, and other devices that use text...

 characters as well as 32 graphics characters. It supported asynchronous communication

Asynchronous communication

In telecommunications, asynchronous communication is transmission of data without the use of an external clock signal, where data can be transmitted intermittently rather than in a steady stream. Any timing required to recover data from the communication symbols is encoded within the symbols...

 at baud

Baud

In telecommunications and electronics, baud is synonymous to symbols per second or pulses per second. It is the unit of symbol rate, also known as baud rate or modulation rate; the number of distinct symbol changes made to the transmission medium per second in a digitally modulated signal or a...

 rates up to 9600 bits per second

Bit rate

In telecommunications and computing, bit rate is the number of bits that are conveyed or processed per unit of time....

 and did not require any fill characters. The terminal also introduced a separate function keypad that allowed "Gold Key" editing (as exemplified by WPS-8

WPS-8

WPS-8 was the name of a Word Processing System sold by Digital Equipment Corporation for use with their PDP-8 processors ....

, KED, and EDT

EDT text editor

There are at least two major text editors named EDT. One was made by Digital Equipment Corporation, the other by what was then Sperry Univac, which later became Unisys.-Digital:...

).

The VT52 offered an optional hard-copy device called an electrolytic

Electrolyte

In chemistry, an electrolyte is any substance containing free ions that make the substance electrically conductive. The most typical electrolyte is an ionic solution, but molten electrolytes and solid electrolytes are also possible....

 copier. This device was able to print, scan-line by scan-line, an exact replica of the screen onto a roll of paper that was saturated with salty water. It did this by electroplating metal from an electrode into the paper. While it did an admirable job of capturing the contents of the screen, the output of the copier had an unfortunate resemblance to wet toilet tissue. Digital patented the innovation of having a single character generator

Character generator

A character generator, often abbreviated as CG, is a device or software that produces static or animated text for keying into a video stream. Modern character generators are computer-based, and can generate graphics as well as text...

 provide the text font

Font

In typography, a font is traditionally defined as a quantity of sorts composing a complete character set of a single size and style of a particular typeface...

 for both screen and copier.

Stages of development

The VT50 was the first terminal Digital produced in this cabinet. It provided only 12 lines of text (leading some users to object to the "double-spacing") and, like the predecessor VT05

VT05

The VT05 was the first free-standing CRT computer terminal from Digital Equipment Corporation. Famous for its extremely futuristic styling, the VT05 presented the user with an upper-case only 5x7 dot-matrix display of 20 rows by 72 columns. The terminal only supported forward scrolling and direct...

, did not support lowercase letters. Computer users of that era used coding in the rare instance that they needed lowercase text. Opinion differed as to whether the VT50 was to be a dry run for the engineers or a lucrative product. The introduction of the VT52, and its support of lowercase text on the screen and scrolling both upward and downward, enabled WYSIWYG

WYSIWYG

WYSIWYG is an acronym for What You See Is What You Get. The term is used in computing to describe a system in which content displayed onscreen during editing appears in a form closely corresponding to its appearance when printed or displayed as a finished product...

 ("What you see is what you get") text editing.

The large size of the cabinet was deliberate, to avoid a cooling fan. The two circuit boards with processor and memory at the base of the terminal, and a single board with power-supply and monitor electronics at the rear, were cooled by unforced air. The large, flat top of the terminal frequently accommodated large volumes of DEC documentation.

These terminals used a primitive, custom central processing unit

Central processing unit

The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...

 built from small-scale-integration integrated circuits. It was so basic that addition and subtraction could only be done by repeatedly incrementing or decrementing two registers, and only while a raster scan

Raster scan

A raster scan, or raster scanning, is the rectangular pattern of image capture and reconstruction in television. By analogy, the term is used for raster graphics, the pattern of image storage and transmission used in most computer bitmap image systems...

 was not in progress. Moreover, the time taken by such a program loop had to be nearly constant, or text lower on the screen would be displayed in the wrong place during that refresh. Display of text was not done under microprogram control; the microprogram activated separate hardware to take exclusive access to screen memory and waited until a line of pixels was complete.

The VT52 became a platform on which Digital built several related devices. The VT55 incorporated an add-on graphics system that was capable of displaying two mathematical functions or histogram

Histogram

In statistics, a histogram is a graphical representation showing a visual impression of the distribution of data. It is an estimate of the probability distribution of a continuous variable and was first introduced by Karl Pearson...

s.

The VT61 and VT62 were block-mode terminals optimized for typesetting

Typesetting

Typesetting is the composition of text by means of types.Typesetting requires the prior process of designing a font and storing it in some manner...

 applications. They used the same cabinet but had a more complete custom processor. Application-specific behavior was coded in separate PROM

Programmable read-only memory

A programmable read-only memory or field programmable read-only memory or one-time programmable non-volatile memory is a form of digital memory where the setting of each bit is locked by a fuse or antifuse. Such PROMs are used to store programs permanently...

 memory, using a separate instruction code that the processor interpreted. This unpublished language was to be used to easily develop additional models specific to single Digital marketing organizations. These terminals synthesized a "tock" sound on a speaker for feedback when a key was pressed, whereas the VT5x activated a relay. The relay was also used as a buzzer to sound the bell character

Bell character

A bell code is a device control code originally sent to ring a small electromechanical bell on tickers and other teleprinters and teletypewriters to alert operators at the other end of the line, often of an incoming message...

, producing a sound that "has been compared to the sound of a '52 Chevy

Chevrolet

Chevrolet , also known as Chevy , is a brand of vehicle produced by General Motors Company . Founded by Louis Chevrolet and ousted GM founder William C. Durant on November 3, 1911, General Motors acquired Chevrolet in 1918...

 stripping its gears." Though the keyboards were identical, VT6x users admired the superior "feel."

The VT78 added to the VT52 a single-chip PDP-8

PDP-8

The 12-bit PDP-8 was the first successful commercial minicomputer, produced by Digital Equipment Corporation in the 1960s. DEC introduced it on 22 March 1965, and sold more than 50,000 systems, the most of any computer up to that date. It was the first widely sold computer in the DEC PDP series of...

 processor, on which was programmed WPS-8

WPS-8

WPS-8 was the name of a Word Processing System sold by Digital Equipment Corporation for use with their PDP-8 processors ....

, Digital's word processing

Word processing

Word processing is the creation of documents using a word processor. It can also refer to advanced shorthand techniques, sometimes used in specialized contexts with a specially modified typewriter.-External links:...

 system. This model was not a terminal to use to communicate with a computer, but a complete, stand-alone system. Whereas the VT50 was developed in the era before it was common to apply computers to text, the VT78 was a product designed for that application.

The VT52 family was followed by the much more sophisticated VT100

VT100

The VT100 is a video terminal that was made by Digital Equipment Corporation . Its detailed attributes became the de facto standard for terminal emulators.-History:...

.