Prestel

For the publisher, see Prestel Publishing.

For the artist, see Maria Katharina Prestel.

Prestel

Prestel logo designed by Mervyn Kurlansky of Pentagram
Developer	Post Office Telecommunications
Key people	Samuel Fedida
Type	General-purpose public videotex service
Launch date	1979 (1979)
Discontinued	1994 (1994)
Platform(s)	GEC 4000 minicomputers in a star network configuration with packet-switched connections
Operating system(s)	OS4000 operating system supporting BABBAGE high-level assembly language
Status	Discontinued
Members	c. 90,000 subscribers at peak
Pricing model	Subscription (quarterly) and usage (time spent on system, some pages, some messaging service actions)

Prestel was the brand name of a videotex service launched in the UK in 1979 by Post Office Telecommunications, a division of the British Post Office. It had around 95,500 attached terminals at its peak, and was a forerunner of the internet-based online services developed in the late 20th and early 21st centuries. Prestel was discontinued in 1994 and its assets sold by British Telecom to a company consortium.

A subscriber to Prestel used an adapted TV set with a keypad or keyboard, a dedicated terminal, or a microcomputer to interact with a central database via an ordinary phoneline. Prestel offered hundreds of thousands of pages of general and specialised information, ranging from consumer advice to financial data, as well as services such as home banking, online shopping, travel booking, telesoftware, and messaging.

In September 1982, to mark Information Technology Year, the Royal Mail issued two commemorative stamps, one of which featured a Prestel TV set and keyboard. In April 1984, British Telecom won a Queen's Award for Technological Achievement for the development of Prestel.

History

Invention and development

In 1970, Samuel Fedida, a research engineer who had worked at English Electric and a US consultancy company, joined the Post Office as head of the Computer Applications Research Division. Within a year, he had completed the initial design of a viewdata system (the generic term in use at the time) for the general public: it would comprise information stored on a central computer accessed over the public phone network using modified televisions as terminals. By early 1973, the Post Office had decided to develop an experimental system, and was working with the BBC, the Independent Broadcasting Authority, and standards organisations to develop compatible standards for teletext and viewdata. During 1974, it decided to commercialise the viewdata concept.

Pilot trial

The first public demonstration of viewdata took place in London in 1975 during Eurocomp, the European Computing Conference on Communications Networks, where Fedida presented a paper on the technology and the potential appeal, as the Post Office saw it, of a public interactive information service.

Further demonstrations followed, and based on the favourable reactions of TV manufacturers and potential providers of information and services, the Post Office decided to run a pilot trial. It also agreed with potential information providers (IPs) that it would not select IPs or exert editorial control over what they put on the system.

The two-year pilot service began in January 1976. By mid-1977, IPs included the Consumers' Association, the British Farm Produce Council, British Rail, London Transport, the Open University, the London Stock Exchange, the Institute for Scientific Information, and National Giro. Interviewed by The Times, Fedida was quoted as saying that the Post Office saw viewdata playing several roles: as a "centralised information source", an "intelligent interface" to specialised scientific and technical data, a "communication machine" for passing messages, a personal information store, a new information distribution medium, a "channel for education in the home", and as providing an "advanced calculator service".

Test service

After some delay, the Post Office launched a test service of Prestel, as it was now called, in October 1978. At the end of December, there were 95,500 information pages, growing at a rate of 3,500 per week, and just over 300 users, increasing by 30–50 per week.

Commercial launch

See also: § Information providers

In March 1979, the Post Office opened a limited "London Residential Service" for subscribers in the capital. The full commercial service launched in September 1979; the director of Prestel stated that there were over 130,000 pages in the database and 1363 "sets" [sic] connected to the system at the start of that month.

By February 1980, there were 131 IPs and 116 sub-IPs. The Post Office categorised the IPs as follows: national and local newspaper groups; magazine and other publishing groups; central government departments, and other agencies (such as the British Tourist Authority and the British Library); nationalised industries (including British Airways, Sealink, and British Rail), and companies in other fields of business, such as banks and travel agencies; new companies set up to exploit the viewdata medium, and those expanding from an existing base of online services, such as Reuters; associations; software companies; and miscellaneous.

Particularly popular were the travel-oriented nationalised industries; new companies, such as Fintel; and the Consumers' Association. Overall, popular topics included games, quizzes, jokes, and horoscopes; the Stock Market, company information, and business news; travel and holiday information; national news, sports, and "What's On" locally; cars; and consumer advice. This was reflected in advertisements for Prestel.

Writing in the winter 1980/81 issue of British Telecom Journal, Prestel's public relations manager stated there were over 7,500 sets attached to the system, 170,000 frames in use, and more than 400 IPs and sub-IPs. By the end of 1981, according to Butler Cox, a management consultancy, Prestel had 2,000 residential and 11,000 business users, with 14,000 "terminals" [sic] in use. The service was within local call reach of 62% of phone subscribers in Britain. IPs numbered 153, with 593 sub-IPs. Users accessed 190,000 frames per day, and the average time on the system, for each user per day, was 9 minutes. There were 193,000 frames available, including 2,000 response frames. § Response frames

March 1982 saw the launch of the Prestel Gateway service. This enabled users to connect, via the Prestel network, to external computers operated by IPs or other companies. Travel agents, for example, used Gateway to connect to tour operators' systems and make reservations.

User charges

At the launch of the commercial service in September 1979, and in addition to phone charges, users were charged 3p per minute online to Prestel from 8 am to 6 pm Monday to Friday, and 3p for three minutes at other times. Installing a jack cost £13, with a quarterly rental of 50p. Business users paid an additional standing charge (i.e., a flat charge regardless of usage) of £12 per quarter.

By October 1982, the online usage charge had risen to 5p per minute (8 am to 6 pm Monday to Friday and also 8 am to 1 pm on Saturdays, free at other times), the business standing charge to £15 per quarter, residential users now paid £5 per quarter, and jack installation cost "from £15", with a 15p quarterly rental fee.

Growth

In September 1982, The Times reported there were 18,000 users, of whom 3,000 were residential. Noting that British Telecom had originally forecast 50,000 users at this point, the report went on to outline a new approach to attracting them, quoting senior managers from British Telecom and the head of a joint venture. The plans involved the introduction of a home banking service; the marketing of a Prestel adaptor for computer terminals to the business and higher education sectors; and the launch of Micronet 800, a service for microcomputer users.

Six months later, in February 1983, the same newspaper recorded 22,400 users, of whom 15% were residential, writing that the future of Prestel "could be in doubt by 1985 if it is not approaching profitability."

In June 1984, the UK Department of Trade and Industry issued a booklet stating that the availability of travel information, the launch of Micronet 800, and the provision nationwide of the messaging service, Mailbox, had contributed to a rise to 45,000 users. 61% were business, and 39% residential. In that month, on average, the Prestel database contained 320,000 frames that were accessed 14.6 million times. For July, the Butler Cox consultancy recorded 47,000 users (60% business, 40% residential), a total of 1,200 IPs and sub-IPs, and 17 external computers accessed via Prestel Gateway.

Database

Pages and frames

Information on Prestel was held in a database of "pages". Each page corresponded to a screenful of information, and had a unique number up to nine digits long. A page could have up to 26 sub-pages, with each sub-page labelled with a letter from "a" to "z". A sub-page was called a "frame": the page itself was frame "a". Neither pages nor frames could scroll.

Each frame had 24 lines of 40 characters each, like the display format used by the Ceefax and ORACLE teletext services. The top line showed the name of the Information Provider (IP), the page number, and the price. The bottom line was reserved for system messages, leaving 22 lines available for the IP to present information to the user.

An IP rented a three-digit number as its master page. For example, the Meteorological Office's was 209, and the numbers identifying all its pages began with these digits – such as for 20971, the page for "Aviation forecasts".

Single- and double-digit pages were reserved by Prestel for system information purposes, such as page 1, which showed the main index. Pages starting with 9 were for account and other system management functions: page 92, for example, showed details of a Prestel user's bill.

When preparing and editing a page, an IP could use upper- and lower-case letters, digits, punctuation marks, a few arithmetic symbols, and a set of "mosaic characters" for composing rudimentary graphics. By embedding cursor-control characters in the page, simple animations could be produced by rewriting parts of the screen already displayed. These were called "dynamic frames".

The IP's name on line 1 occupied at least 43 bytes, depending on the number of control characters involved, so the space available for the IP's data on-screen was a maximum of 877 characters A line could occupy all forty of the character positions available, or be terminated early with a control character. Each control character consumed two bytes, so the more complex the page, the less information could be shown.

Most frames were set up to provide information. Other types were for messaging, or provided a gateway to other computer-based services. A "follow-on" type could also be specified: this caused the following frame to be automatically displayed as soon as the current frame had finished being transmitted. For dynamic frames, this provided a way to continue animations that could not fit within the number of characters available in one frame alone.

This follow-on frame facility was also used for telesoftware, enabling computer programs, such as those for the BBC Micro, to be downloaded from Prestel.

Links

A page could be directly linked to up to ten other pages by specifying, during editing, the number of the page whose content would be displayed when a user pressed a digit from 0 to 9 on their keypad or keyboard. Double-digit links – such as "56" – were achieved by linking the first digit to an intermediate, stepping-stone frame on the IP's database: this, in turn, connected the second digit to the target page.

The content of pages ranged between two poles: at one, a menu listing the topics available and the number to key to reach them, with no, or minimal, further information – referred to as an "index page"; and at the other, a screenful of information with few, if any, links to other pages – an "information page". According to Rex Winsbury, a media journalist and editorial director of Fintel, a major IP, as experience with the viewdata medium grew, IPs "gave information on all or most pages, simply varying the amount according to the number of routings [links] that have to be given as well."

Structures

Original Prestel "inverted tree" database structure: each page could be linked to up to ten other pages

When the public Prestel service began in 1979, a user connecting to the system was presented with the main index page. As they made and keyed successive menu choices, they moved down a subject hierarchy, from the general to the specific, to finish with the information page they sought. The Post Office, academics, and the media referred to this hierarchical database arrangement as a tree structure or "inverted tree".

Links back to the main index were the first refinement made

Though simple in theory, in practice this structure could lead a user to a dead end: they might find that how a subject was described in a menu did not match what they saw on the final destination page, or formed only part of what they were looking for, or provided information without the means to look up related material. Going back through the sequence of menu choices (using the *# command) to try another series of links was limited to three steps in all.

As Prestel developed, IPs accommodated the particularities of the different types of information and services they provided, and the expectations of their users, through the extensive use of backlinks and crosslinks between their pages. This resulted in a variety of database structures that acquired labels such as cartwheels, ring-of-rings, Chinese lanterns and lobster-pots to help visualise how pages were connected.

Navigation and search

front

back

Pocket guide to Prestel for medical practitioners, c. 1984. Their welcome page was 1629. Laminated card, 6.9 x 11 cm

There were three basic navigation commands:

• *number# took the user directly to the first frame of the page number specified: for example, *5052# displayed the contents of 5052a onscreen;
• # moved the user successively forward through the frames: 5052b, 5052c, and so on;
• *# returned the user to the previous page in strict sequence, and could be repeated three times.

Keyword access was introduced in 1987, with *keyword# taking the user directly to the subject (or subject index) specified.

A topic index, updated daily, was published on page 199, and an IP index on page 198. A printed A‍–‍Z directory of the topics available on Prestel, with the appropriate page number to key, was sent to new users. From 1987, the topic names could also be used as keywords. Every two months, users were sent a magazine, Connexions, that included an updated directory, and the directory was also incorporated into the quarterly Prestel Business Directory created by the Financial Times.

Information providers

There were two types of information provider (IP): main IPs, and sub-IPs.

Charges

A main IP rented pages directly from the Post Office (initially) or British Telecom (later), and owned a three-digit node or "master page" in the database. This required an annual payment in 1982 of £5,500 for a basic package, equivalent to around £29,000 in 2021.

The basic IP package included 100 frames; the ability to enter and amend information, retrieve response frames, and store 10 completed response frames; staff training in editing (a two-day seminar), and a copy of the IP editing manual; and, if required, bulk update facilities and an annual print-out of frames in use. Additional frames were available, in batches of 500, for £500 a year (over £2,600 in 2021), while using "Closed User Groups" (CUGs) and the sub-IP facility each cost £250 annually (over £1,300 in 2021).

Sub-IPs – those with smaller requirements or budget – rented pages from a main IP. After paying the additional £250 annual fee, a main IP could rent out individual pages at a market rate. Such IPs were known as "umbrella" IPs. Unlike a main IP, sub-IPs paid a per-minute charge for editing online: in 1982, this was 8p per minute from Monday to Friday between 8 am and 6 pm, and 8p per 4-minute block at all other times (equivalent to around 35p as at end 2014). Sub-IPs were restricted to pages under a 4 or more digit node within a main IP's area, and could only edit existing pages: they were not able to create or delete pages themselves.

Relationships

Several typical relationships developed between umbrella IPs and client sub-IPs:

• The sub-IP was an independent supplier of information, with exclusive or partial editorial control and full or partial editing rights.
• An organisation made information available to an IP, sometimes on a royalty basis.
• An organisation advertised on an IP's pages.
• An individual authored articles or columns for an IP, usually on a royalty basis.

An analysis in 1981 of the pros and cons of using an umbrella IP to publish information on Prestel concluded that if the owner of the information needed less than 500 frames, it would be cheaper to use an umbrella IP, but if over 5000, this would be more expensive than doing it themselves. In between these two figures, speed, convenience, and the need for design skills favoured using an IP, while going it alone assured confidentiality and provided more control.

Editing pages

See also: § Network

Cherry Editing Keyboard manufactured by Cherry GmbH, connected to a Deccafax Viewdata Terminal Model VP1 manufactured (1979–1994) by Decca Radio & Television. Keyboard 11 x 50 x 31 cm, terminal 42 x 45 x 45 cm, 28 kg

There were two ways to edit pages: directly, by creating or amending them using special editing keyboards while connected online to the main Update Computer; or offline, creating pages locally and uploading them in bulk. Bulk update required that pages be created offline using editing terminals that could store pages, or by using microcomputers. The pages were then either transmitted to the Update Computer online as a batch via a special dialup port and protocol, or sent on magnetic tape to the Update Centre (UDC), where they were uploaded.

Using the online editor, IPs were also able to view information about a page hidden from ordinary users, such as the time and date of its last update, whether the frame was in a Closed User Group (CUG), the price-to-view (if any), and the "frame count" – the number of times the frame had been accessed.

IPs and sub-IPs accessed the Edit computer using their normal ID and password, but had a separate password to access the editing facility. Bulk uploads only required the edit password and the IP's account number.

Information and services

Prestel's pre-launch promotional material focused on the general public:

Prestel is for everyone. Busy mothers can check out prices before they go shopping or their children can use Prestel to help them with their homework. Gardeners will have a constant source of information on what they should be doing at any particular time of the year. Whole families can choose and even book their holidays through Prestel. [..] Prestel will provide you with listings for theatres, cinemas, sporting events, exhibitions and just about anything else that may be going on.

When the service launched in late 1979, Post Office Telecommunications had a hands-off approach towards managing whatever IPs placed on the system. This changed in early 1980, when British Telecom (its successor) started targeting the business, professional and hobbyist markets via joint ventures with companies and organisations with specialised expertise.

By the mid-1980s, the specialised services on Prestel included:

• Prestel CitiService, involving the London Stock Exchange and ICV Information Systems, targeted three groups: the business community as a whole, with mainly company information; private investors in a closed user group, offering regularly updated share prices; and for brokers and other investment professionals, continuously updated share prices, also in a closed user group.
• British Telecom Travel Service provided travel agents with information from tour operators, airlines, and other transport operators, and enabled online reservations. The service for other users included flight arrivals and departures, car rental, and exchange rates.
• Prestel Farmlink packaged information for farmers from the Ministry of Agriculture, Fisheries and Food, the Meat and Livestock Commission, the Meteorological Office, and others. A link to Prestel CitiService provided farm commodity prices, and farmers could calculate, online, weekly wages and the formulation of feedstuffs.
• Banking: the Nottingham Building Society offered Homelink, and the Bank of Scotland HOBS, the Home & Office Banking Service. Subscribers were provided with free or subsidised Prestel terminals.
• Prestel Microcomputing offered downloadable software (telesoftware), noticeboards, newsletters, and reviews. It incorporated Micronet 800 from EMAP, Viewfax 258, and Clubspot 810.
• Prestel Education targeted schools and colleges, and provided course and careers advice, educational software, and help with using computers.
• British Telecom Insurance Services provided financial information to insurance intermediaries and enabled them to get online quotes from major insurance companies.
• Prestel Teleshopping was a specialised e-commerce service for the residential market, and involved Littlewoods and Kays Catalogues, among others.

Messaging

Response frames

A "response frame" enabled a user to send a message to an IP using a special preformatted page, for example to order goods or services. The user's name, address, and phone number were automatically added to the frame by means of embedded codes that triggered the extraction of this data from their Prestel account.

Initially, response frames had to be collected by an IP from each IRC in turn; later, they were ingathered at the UDC, where the IP concerned could retrieve them. Eventually, with the introduction of Mailbox, response frames could be retrieved from any IRC. § Network

Mailbox

Launch version of Prestel Mailbox entry page, *7# (1983).

Prestel Mailbox was launched in 1983. Initially hosted on a computer in London, it was later made available UK-wide. § Network

The entry page for Prestel Mailbox was *7#. This linked to pages where new messages could be composed, stored messages retrieved, and standard, pre-formatted messages completed – many designs were available, including greetings cards and seasonal messages such as valentines.

To prepare a basic message, a blank message page (directly accessible via *77#) was displayed, with the sender's Mailbox number pre-filled and blank fields shown for entering the recipient's number and the message text. As messages could only occupy a single frame, there was space for up to 100 words or so, and fewer if graphics were used. After addressing (with a Mailbox number) and writing the message, the user was offered the choice of keying 1 to send it, or keying 2 to not send it. Successful dispatch led to a confirmation page; if there were problems, such as a mistake in entering the recipient's Mailbox number, an error message was displayed. To send the message to more than one recipient meant re-keying the text into a fresh message frame, although some microcomputers allowed the original message to be stored and then copy-pasted instead.

Screenshot of a received message. The name of the host computer, "Enterprise", is at top-right. The Mailbox numbers start with 01999, so are ex-directory. The bottom of the screen shows instructions for storing or deleting the message.

Prestel Mailbox numbers were based on the last nine digits of a user's phone number. For example, the Mailbox number for Prestel HQ, with the phone number 01-822-2211, was 018222211, while for a user in Manchester with the number 061-228-7878, it was 612287878. In keeping with phone directory practice at the time, Prestel Mailbox numbers were published in a list accessible from page *486#. Ex-directory Mailbox numbers were available on request.

Prestel Mailbox promotional badge, c.1983. Metal, 5.6 cm diameter

When a user connected to Prestel, a Mailbox banner on their Welcome page alerted them if they had any new messages. Similarly, when a user signed off via *90#, a warning would appear if any new messages had arrived in the meantime, with the option to read them before disconnecting. Messages were retrieved from page *930#, where they were presented in chronological order. After reading a new message, a user had to choose between deleting or saving it before the next message was presented. Initially, only three messages could be saved at a time; these stored messages were accessible via page *931#.

Using this first version of the basic Mailbox service was free of charge. § Mailbox upgrade

Telex Link

Prestel Mailbox was extended in 1984 to give access to the Telex service via "Telex Link". On *8#, the Telex Link entry page, a message could be composed, the destination country chosen, and the telex number entered before sending the telex like a standard message. Telex Link added the necessary telex codes and tried to send the message several times before confirming receipt (or failure) via Mailbox.

A telex could be sent to a Mailbox user from any telex terminal by using 295141 TXLINK G, the Telex Link number, as the telex address, and entering "MBX", followed by the Prestel user's Mailbox number, as the first line of the telex. An incoming telex appeared to the Prestel recipient as an ordinary Mailbox message, with the telex number of the sender added at the top of the screen.

Sending a telex cost 50p for UK destinations, £1.00 for Europe, £2.00 for North America, £3.00 for elsewhere in the world, and £5.00 for sending to ships (via INMARSAT). There was no charge for receiving one.

Telex Link was upgraded in 1987, with connections to more telex lines and faster delivery times, and its address changed to 934999 TXLINK G.

Mailbox upgrade

A new messaging system was introduced in July 1989. This enabled messages up to five frames long, storing messages before sending, sending to multiple recipients (either individually or via a mailing list), message forwarding, and acknowledgment of receipt.

Sending a basic message without using any of these new facilities remained free: all the new options were charged at 1p per use per recipient. For the first time, sending spam was permitted at a cost of 20p per message per recipient. In addition, the stored message facility was replaced by a summary page listing all the messages, both new and old, that were waiting: the user could then pick which message to view, rather than needing to read through them in chronological order.

Message statistics

By 1984, Prestel users were sending messages at the rate of around 71,000 per month via a computer in London. In September 1985, after Mailbox became a national service, the chief executive of the part of British Telecom responsible for Prestel stated that 100,000 "electronic mail messages" were being sent each week, with 60,000 terminals attached to the system.

Hack

A security breach of the Prestel mailbox of Prince Philip, Duke of Edinburgh occurred in November 1984 as part of a wider hack of Prestel.

Infrastructure

Network

Configuration and growth

In March 1979, the Post Office launched a limited "London Residential Service" for subscribers in the capital. This was based on the computer used in an earlier test phase to both store the Prestel database and enable IPs to make updates to their pages.

When the full commercial service launched in September 1979, three new computer centres were opened in London. Two, known as Byron and Juniper, were "Information Retrieval Centres" (IRCs): their computers each contained a copy of the Prestel database, and were accessible by users. The third, Duke, was Prestel's "Update Centre" (UDC): IPs used this to create, modify or delete their pages, with their updates sent to the IRCs. A fourth IRC, Dickens, opened in Birmingham in December.

IRCs were connected to the UDC in a star network configuration using leased-line connections (based on the X.25 protocol) operating at 2400 baud. This network handled about 2,000 Prestel terminals and provided users with over 160,000 pages supplied by around 130 IPs. By mid-1981, this arrangement had been replaced by dedicated X.25 circuits using the then-new PSS packet-switched network and operating at 4.8 kbit/s.

Each IRC typically housed two information retrieval computers, though some in London had a single machine. IRCs were usually located in major telephone exchanges, rather than data-processing centres, to accommodate the extensive communications equipment needed: exchange buildings could more easily house the large numbers of rack-mounted 1200/75 baud modems and associated cabling required, as well as the GEC multiplexers connecting the modems to the computers.

By June 1980, the network had grown to four individual information-retrieval computers in London, and six others installed in pairs in each of Birmingham, Edinburgh and Manchester, making ten in all. These ten computers could initially connect to around 1000 user ports, expandable to 2000. At this point, the Prestel database contained about 164,000 pages with expandability to up to 260,000 built in: allowing for system management pages, this arrangement capped the size of the public database at around 250,000 frames.

By September 1980, there were five IRC machines in London and pairs of machines in Birmingham, Nottingham, Edinburgh, Glasgow, Manchester, Liverpool and Belfast, offering a total of 914 user ports. Further IRCs were planned in Luton, Reading, Sevenoaks, Brighton, Leeds, Newcastle, Cardiff, Bristol, Bournemouth, Chelmsford and Norwich by the end of 1980.

By the end of 1980, 1500 user ports were available. By July 1981, the number of IRC computers had grown to 18: this increased the proportion of phone subscribers who could dial-up Prestel at local rates from 30% to 62%. By 1984, the short dialling codes 618 and 918 could be used in most of the UK for access at local call rates.

International access

In late 1981, an IRC called Jefferson opened in Boston, Massachusetts, giving US subscribers access to Prestel via the American Telenet packet-switched network.

Mailbox computer

See also: § Mailbox

Mailbox, the Prestel messaging service, was launched on Enterprise computer, and allowed messaging only between users accessing that machine. By 1984, Mailbox had been rolled out nationwide using a dedicated computer in London known as Pandora.

Hardware

Prestel's computers were based on the GEC 4000 series minicomputer. The main IRC machines were originally model GEC 4082s equipped with 384 Kbyte memory-core stores, six 70 Mbyte hard disk drives, and 100 ports. This set-up accommodated an initial 1500 Prestel users.

Each IRC computer had 208 ports. With eight reserved for testing and control, a computer could support up to 200 simultaneous Prestel users. For the ordinary user, access was via an asynchronous, duplex interface provided by banks of multiplexers. These, in turn, were accessed via standard modems, operating at 1200/75 bit/s, directly connected to the public phone network.

Besides the multiplexers required to support 1200/75 dial-up access, the Update Centre machines were also connected to special modems that handled online bulk updating by IPs. Banks of 300/300 bit/s full-duplex asynchronous V.21 modems supported direct IP-computer-to-Prestel-computer links, while 1200 bit/s half-duplex V.23 modems supported access by IPs using editing terminals that stored frames offline before uploading them. In addition, twin 9-track NRZI tape decks of 800 bytes/inch capacity were provided for bulk offline updates.

GEC 4000 series computers at GEC Computers' Dunstable Development Centre, 1991

Though categorised as a minicomputer, GEC 4000 series machines were large: one occupied several standard computer cabinets each standing 6 feet (1.8 m) high by 2 feet (0.61 m) wide. The CDC 9762 hard disc drives were housed separately in large, stand-alone units about the size of a domestic washing machine. A GEC machine cost over £200,000 at standard prices, in addition to which were the costs of the associated communications equipment. Combining the two to assemble a single IRC was a major undertaking, and took some 15 months from order placement to commissioning.

Software

GEC 4000 series computers could run on several operating systems. The Prestel machines used OS4000, which was developed by GEC and supported BABBAGE, the high-level assembler in which all Prestel software was written.

The pilot-trial system had five core software components: INPUT process, OUTPUT process, GATE-KEEPER process, DISC-handler process, and several TASK processes. INPUT received data from a Prestel user; GATE accepted characters, one at a time, from INPUT and fed them to a TASK; the key frame-getter TASK fetched a fresh page or the next frame of an already-displayed page from DISC. OUTPUT then displayed a whole frame, preceded by a clear-screen command, to the user.

The commercial service had several important additional functions, including an editing program and bulk update facilities, closed user groups, messages, user billing and IP revenue allocation, optional additional user passwords, error-reporting routines, system manager facilities, and statistics-collecting routines.

In 1987, a Prestel Admin computer was introduced to support the user registration process. It captured a new user's details from the paper Prestel application form, transferred the data to the relevant Prestel computer, and then printed the welcome letter to be sent to the user concerned.

Monitoring

Users' connections to Prestel were monitored by a device known as VAMPIRE – Viewdata Access Monitor and Priority Incident Reporting Equipment. Via private circuits connected to an IRC computer's ports, this produced a continuously updated display on a monitoring screen at the Prestel Regional Centre responsible for an IRC. The screen showed a matrix of small squares, each corresponding to a port on an IRC computer. Free ports were green, occupied ones yellow, incoming calls-to-connect by Prestel users were pale blue, and faulty ports red. In this way, the overall status of an IRC machine could be summarised and seen at a glance.

The response time of the Prestel system was measured by a microcomputer-based device known as PET. This monitored frame retrieval times for users and how quickly frame-editing commands issued by IP editors were implemented. PET operated in conjunction with a hardware performance monitor that recorded central processing unit and disk-drive usage.

Public take-up

Writing in early 1979 about the test service that had launched in October 1978, a Post Office executive concluded that:

"The strengths of viewdata include its visual attractiveness, its ease of use, low cost and its wide range of applications. Its weaknesses include its small information window, unsophisticated search methods, its limited storage capacity and its lack of computer power for users. How rapidly viewdata will become established, and the exact role it will fulfil, is as yet a matter of speculation."

While teletext services were provided free of charge as part of regular television broadcasts, Prestel was transmitted via telephone lines to a set-top box, computer, or dedicated terminal: gaining access to the service involved arranging for a Post Office engineer to first install a connection point known as a Jack 96A. Thereafter it was necessary to pay both a monthly subscription and the cost of local telephone calls. On top of this, some content was sold on a paid-for basis: each Prestel page carried a price in the top right-hand corner, and a single page could cost up to 99 pence.

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 expensive. Eventually set-top boxes became available, and some organisations supplied these as part of their subscription package: for example, branded Tandata terminals were provided by the Nottingham Building Society for its customers, who could make financial transactions via Prestel.

Prestel terminal

Because the transmission of Prestel over telephone lines did not use an 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.

Regardless of the hardware, Prestel was expensive, and as a result, only gained limited market penetration, with a total of around 90,000 subscribers at its peak. The largest user-groups were Micronet 800 with 20,000 and Prestel Travel with 6,500 subscribers respectively.

Having developed Prestel as a way of maximising telephone line use, the Post Office and subsequently British Telecom provided only the framework for Prestel, delegating the provision of information to information providers. Nevertheless, considerable investment was required in Prestel's infrastructure, though with information providers paying rental charges and users installation and rental fees, the outcome was considered likely to be profitable. A mass public service was envisaged, with considerable public take-up, but a lack of compelling content and services gave domestic users, in particular, the impression that Prestel was something that would cost a lot for relatively little in return. That said, it was predicted that eventually "Prestel – or another viewdata system – will be ubiquitous."

International sales

The Prestel system was sold to several countries, including Austria, Australia, former West Germany, the then-British colony of Hong Kong, Hungary, Italy, Malaysia, the Netherlands, New Zealand, Singapore, and former Yugoslavia.

Telecom Australia re-branded their system Viatel, with the centre of operations in Windsor, Melbourne, Australia. During the Black Monday stock market crash the system's stock trading system was highly used. The system in Italy run by SIP was heavily used during the 1990 FIFA World Cup for reporting the match progress and scores. The Singapore system provided a much higher receive bandwidth than was available over dial-up modems at the time by broadcasting the return frames using the Teletext technique of embedding them in broadcast television signals. Four VHF TV channels were dedicated to this with all the scan lines used for Teletext encoding, which enabled the system to provide a feature called Picture Prestel to convey higher resolution images. The Yugoslav system was based in Zagreb, with additional IRCs located in Rijeka, Ljubljana, and Split.

The American Viewtron videotex service was modelled after Prestel.

See also

• Bildschirmtext – German videotex service
• Micronet 800 – 1980s online magazine on Prestel
• Minitel – French videotex service
• Singapore Teleview – Singaporean videotex service
• Telidon – Canadian videotex/teletext service
• videotex – End-user information system

Further reading

• Davenport, Lucinda D. (2023). "The Viability of Viewdata as a Mass Medium: A Case Study of Prestel, the Prototype for Computerized Information Systems, the Internet". TMG Journal for Media History. 26 (2): 1–29. doi:10.18146/tmg.845. ISSN 1387-649X. Examines the development, marketing, and public reception of Prestel within the digital platform economy emerging at the time.

• Lean, Tom (2016). "Chapter 6: Two Information Revolutions That Weren't". Electronic dreams: how 1980s Britain learned to love the computer. London: Bloomsbury Sigma. pp. 143–174. ISBN 978-1-47291-833-8. OCLC 944121056. The chapter covering Prestel describes its history in the context of the 1980s boom in Britain of home computing, and has a particular focus on marketing strategies.

• Williams, Raymond (2010) [1st ed. 1974, 2nd ed. 1990]. Williams, Ederyn (ed.). Television: Technology and Cultural Form (2nd (reprinted) ed.). London: Routledge. ISBN 978-0-415-31456-5. OCLC 846446460. Surveys the social history of television as a developing technology and the social history of how what was developed was used; anticipates – from a mid-1970s perspective – potential innovations (including "interactive devices"); and provides an overview of the situation in 1990.

• Rutter, Dorian James (2005). "Chapter 4: Before the Internet: the Rise and Fall of Prestel" (PDF). From Diversity to Convergence: British Computer Networks and the Internet, 1970–1995 (PDF) (PhD thesis). University of Warwick. pp. 105–158. OCLC 93065596. Analyses the evolution of British computer networks and the Internet between 1970 and 1995, with the Prestel chapter focusing on Prestel's communications infrastructure, how this enabled the services offered, and marketing decisions and campaigns.

• Reid, Alex; Clarke, Keith; et al. (1981). Winsbury, Rex (ed.). Viewdata in Action : a Comparative Study of Prestel. London: McGraw-Hill. ISBN 978-0-070-84548-0. OCLC 715473323. This multi-authored work covers relations between the interest groups involved in providing a videotex service on Prestel, videotex's impact on the press, editorial issues, economic aspects, and likely technological developments.

• Winsbury, Rex (1979). The Electronic Bookstall : Push-button publishing on videotex: a critical study of Prestel in Britain. London: International Institute of Communications. ISBN 978-0-904-77610-2. OCLC 5507588. Focuses on the practicalities and economics of creating information on Prestel, and on Prestel's relationships with the British newspaper and broader print publishing industry of the late 1970s.

• Fedida, Samuel; Malik, Rex (1979). The Viewdata Revolution. London: Associated Business Press. ISBN 978-0-852-27214-5. OCLC 6387998. Co-authored by one of Prestel's inventors, Samuel Fedida, this describes the genesis and context of viewdata, the components of the initial Prestel service, and potential developments from the perspective of 1979.

External links

• A User's View of Prestel in an archived copy of Creative Computing magazine

• Prestel at Celebrating the Viewdata Revolution

• Objects catalogued under "telecommunications /Prestel" and "computing & data-processing /Prestel in the Science Museum Group's collections

• Catalogue records with "Prestel" in the title in BT Group's digital archives