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. Initial development 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. Database 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. Thus there remained 22 lines (of 40 characters each) in which the IP could present information to the end user. A page should be considered as a logical unit of data within the database and the frame a physical unit. Unfortunately the terms node, page