Prestel
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Prestel (abbrev. from press telephone), the brand name for the UK Post Office's Viewdata technology, was an interactive videotex system developed during the late 1970s and commercially launched in 1979.
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[edit] Initial developers
The innovations on which it was based were credited to Samuel Fedida at the then Post Office Research Station in Martlesham, Suffolk. In 1978 a team of programmers was recruited from within the Post Office Data Processing Executive. Under the management of David Wood they developed the software for the public access Prestel system. In 1983 as privatisation of British Telecom loomed the staff of the software development team were moved into the Prestel Division of BT.
[edit] How it worked
In common with the Ceefax and ORACLE teletext services provided by the BBC and ITV television companies, the system used a modified television to display information in a non-scrolling window of 40x24 text characters, with some simple graphics, conforming to the 1981 CEPT1 standard. Unlike the restricted number of pages available on Ceefax and Oracle, Prestel offered an extensive range of information that had been supplied both by a Prestel department at the Post Office and by third-party information providers.
The range of Information Providers (or IPs) was wide, including: news services, travel companies (serving both the public and travel agents), estate agents, banks and financial services, those providing stock market information, the government and Parliament. The IPs entered their information on a central Update Computer, "Duke", located in London. The information was distributed, via an early X.25 packet switching network, to a number of "Information Retrieval Centres" (IRCs) that were distributed throughout the UK, each of which maintained a mirrored copy of the central database.
These IRC machines, located in major telephone exchanges, were known by code names such as "Dryden", "Kipling", "Derwent", "Enterprise", "Dickens", "Keats", "Bronte", "Eliot" and "Austen" (among others). It was the IRC computers that were accessed, at local phone-call rates, by the "ordinary" users retrieving pages of information.
Each page was divided into a series of screen-sized blocks. The user could retrieve the next block of a page by pressing the "#" key. Each block could have up to ten links to other pages. The reader accessed the linked pages by using the digits "0" to "9" on their keypad. They could also issue commands from a limited repertoire known as "star commands" as each was prefixed by the "*" key. For example "*#" meant "go back to previous block (or page)" and "*123456#" meant "go directly to page number 123456". Hence with only a numeric key pad (and no mouse) a user could navigate a web of pages, much as, in the present day, people navigate the World Wide Web.
Access was open to all users except for pages that were allocated to a number of CUGs (Closed User Groups). Membership of each CUG was provided to a controlled userbase, usually as a paid subscription. Mail was handled by a machine known as "Pandora".
All of the Prestel computers (both the Central Update machine and the IRC machines in the telephone exchanges) were GEC 4000 series minicomputers running OS4000, and the Prestel software was written in Babbage high-level assembly language. Typically an IRC with 1Mb of main memory would support up to 256 simultaneous users sessions.
[edit] Public take-up of the service
Whilst teletext services were provided free of charge, and were encoded as part of the regular television transmissions, Prestel data was transmitted via telephone lines to a set-top box terminal, and while this enabled interactive services and a crude form of e-mail to be provided, it also involved purchasing a suitable terminal, and paying both a monthly subscription and the cost of local telephone calls. On top of this, some services (notably parts of Micronet800) sold content on a paid-for basis. Each Prestel screen carried a price in pence in the top right-hand corner. Single screens could cost up to 99p.
The original idea was to persuade consumers to buy a modified television set with an inbuilt modem and a keypad remote control in order to access the service, but no more than a handful of models were ever marketed and they were prohibitively expensive. Set-top boxes were pioneered by the Nottingham Building Society for its customers, who could make financial transactions via Prestel.
The access situation improved as home computers became more commonplace, and by the late 1980s it was possible to use a machine such as a BBC Micro or Atari computer, equipped with a 1200/75 baud modem and some simple software, to access the Prestel service. Even the more gaming-orientated Sinclair ZX Spectrum had a large number of users via a low-cost modem called the VTX-5000. It was possible to buy downloadable content such as simple games. This would be encoded in a series of pages that were not human-readable, but encoded in blocks of rather less than 1 kilobyte per page. The header and footer of these pages was normal, however, so users could watch the pages appearing one after another to build up the downloaded file. To charge for content, the pages of the downloaded file were charged at 99p each until the total charged was within 99p of the total price, after which one page was charged at the balance of the total price and the subsequent pages were free.
Because the communication over telephone lines did not use any kind of error correction protocol, it was prone to interference from line noise which would result in garbled text. This was particularly problematic with early home modems which used acoustic couplers, because most home phones were hard-wired to the wall at that time.
However, it was still an expensive proposition, and as a result, Prestel only ever gained a limited market penetration among private consumers, achieving a total of just 90,000 subscribers, with the largest user groups being Micronet800 with 20,000 users and Prestel Travel with 6,500 subscribers.
The BT Prestel software development team developed a number of national variants of Prestel, all of which ran on GEC Computers. They were sold to the PTTs of other countries, including Austria, Belgium, Italy, Hungary, Hong Kong, Germany, Netherlands, Singapore, Yugoslavia, [incomplete list]. Italy was the largest system with 180,000 subscribers. The Singapore system had a notable technology difference in that pages were not returned over the modem connection, but were returned using teletext methods over one of four TV channels reserved specially for the purpose, which had all scan lines encoded in teletext format. This higher bandwidth enabled use of a feature called Picture Prestel which was used to carry significantly higher resolution pictures than were available on other Prestel systems.
In 1990, BT introduced a new commercial model which effectively killed the domestic usage of the service, charge per-minute charges for access on top of the user's existing phone bill. Finally in 1991 it was decided that BT should move away from providing Value Added Services and should focus on network provision. Consequently the various consumer and business services were run down or sold off with such services as Prestel Travel and BTIS (BT Insurance Service) becoming private network services for third-party providers.
The 1984 hacker intrusion into the (very likely unused) Prestel mailbox of the Duke of Edinburgh garnered the network some unfavourable press, particularly when the simplicity of its security measures became apparent. The subsequent failure to successfully prosecute the intruders contributed to the introduction of the Computer Misuse Act 1990.
The Prestel name and equipment was eventually sold by British Telecom, and purchased by a private company, Financial Express, in 1994 and renamed New Prestel. During this period, the platform software was redeveloped onto a SCO Unix and Linux x86 platform away from the GEC 4000 Mini Computers. Additionally, the Citiservice financial data product was successfully redeveloped in house after being outsourced to Datastream during the time with BT.
Prestel Online, which was an Internet service provider spinoff, was sold to Scottish Telecom, and as of 5 June 2002, has since been merged into their other ISP activities.
The dial-up viewdata service was run down as the Internet gained in popularity.
[edit] Successes
In contrast to the demise of the British system, the French equivalent of Prestel, Teletel/Minitel, which used the slightly superior CEPT2 standard, received substantial public backing when millions of Minitel terminals were handed out free to telephone subscribers (causing Alcatel huge financial problems). As a consequence the Teletel network became very popular in France, and remains well used, with access now also possible over the Internet.
A closed access videotex system based on the Prestel model was developed by the travel industry, and continues to be almost universally used to this day by travel agents throughout the country: see Viewdata. The Prestel technology was also sold abroad to several countries, and in 1984 Prestel won a UK Queen's Award for Industry both for its innovative technology and use of British products (it largely ran on equipment provided by GEC Computers).
[edit] Homelink
In 1983 the UK's first online banking service opened with Homelink, which was a cooperation between the Nottingham Building Society and the Bank of Scotland.
[edit] References
- Fedida, S. and Malik, R. (1979). The Viewdata Revolution. London, UK, Associated Business Press, ISBN 0-85227-214-6
[edit] See also
- Compunet
- World War II Colossus computer, also built by the Post Office Research Laboratories.
