Prestel (abbrev. from press telephone), the brand name for the UK Post Office Telecommunications's Viewdata technology, was an interactive videotex system developed during the late 1970s and commercially launched in 1979. It achieved a maximum of 90,000 subscribers in the UK and was eventually sold by BT in 1994.
The technology was a forerunner of on-line services today. Instead of a computer, a television set connected to a dedicated terminal was used to receive information from a remote database via a telephone line. The service offered thousands of pages ranging from consumer information to financial data but with limited graphics.
Prestel was created based on the work of Samuel Fedida at the then Post Office Research Station in Martlesham, Suffolk. In 1978, under the management of David Wood the software was developed by a team of programmers recruited from within the Post Office Data Processing Executive. As part of the privatisation of British Telecom, the team were moved into a "Prestel Division" of BT.
Prestel databases is commonly referred to as the 'tree structure'. The structure is shown pictorially as an inverted tree with the data considered as 'leaves' of the tree, accessed via 'branches' which serve as a means of classifying the information. There exists quite a lot of jargon regarding such structures but in order to appreciate the concept it is necessary to mention just the node, page and frame. Nodes are the junction pages in the tree at which a number of choices can be made leading to other nodes or to the information itself. Pages are the final levels in the tree and contain the actual data-these may be divided into frames which are really screenfuls of information.
The public Prestel database consisted of a set of individual frames, which were arranged in 24 lines of 40 characters each, similar to the display used by the Ceefax and ORACLE teletext services provided by the BBC and ITV television companies. Of these, the top line was reserved for the name of the Information Provider, the price and the page number, and the bottom line was reserved for system messages.
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Teletext, or broadcast teletext, is a standard for displaying text and rudimentary graphics on suitably equipped television sets. Teletext sends data in the broadcast signal, hidden in the invisible vertical blanking interval area at the top and bottom of the screen. The teletext decoder in the television buffers this information as a series of "pages", each given a number. The user can display chosen pages using their remote control.
The Minitel was a videotex online service accessible through telephone lines, and was the world's most successful online service prior to the World Wide Web. It was invented in Cesson-Sévigné, near Rennes, Brittany, France. The service was rolled out experimentally on 15 July 1980 in Saint-Malo, France, and from autumn 1980 in other areas, and introduced commercially throughout France in 1982 by the PTT (Postes, Télégraphes et Téléphones; divided since 1991 between France Télécom and La Poste).
Videotex (or interactive videotex) was one of the earliest implementations of an end-user information system. From the late 1970s to early 2010s, it was used to deliver information (usually pages of text) to a user in computer-like format, typically to be displayed on a television or a dumb terminal. In a strict definition, videotex is any system that provides interactive content and displays it on a video monitor such as a television, typically using modems to send data in both directions.