About Prestel

April 22, 2013 // Posted in Main  

In my first post I mentioned Prestel, and some readers have asked for more information on what it was and what it did, so here goes:


Prestel Logo

Prestel Logo

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.

Prestel was the GPO, later British Telecom’s, answer to teletext.  With two-way communications between user and servers, many more pages could be offered, and user interaction could be achieved through response frames to the Information Providers, user to user emails, and public chat lines.  It was launched in 1979.

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 Information Provider (IP) could present information to the end-user. Each frame was stored in a block of 1 kilobyte (1024 bytes), out of which at least 104 bytes were reserved for routing and system information. This left 920 bytes for the frame contents, 716 bytes in the case of response frames. The IP logo on line 1 occupied at least 43 bytes, depending on the number of control characters, so the space available for the IP’s data is 877 characters at most. Lines could either occupy the full forty character positions, or be terminated early with a CR/LF sequence. Each control character took up two bytes, despite displaying as a single space, so the more complex a page, the less actual information could be presented. It was almost impossible, therefore, to display a right hand border to a page.

Available characters consisted of upper and lower case alphanumeric characters as well as punctuation and simple arithmetic symbols, using a variant of ISO 646 and CCITT standard. This layout was later formalised in the 1981 CEPT videotex standard as the CEPT3 profile. In addition, mosaic graphics were available in which individual character positions were divided into six squares which could be used in any combination, giving the possibility of 64 different graphics characters. Alphanumeric characters or mosaics could be entered in white or any one of six foreground colours (red, blue, green, yellow, cyan, magenta) and set against a background of the same colours as well as black. Special control symbols were employed so that characters or mosaics could be made to flash, appear double height, be separated by a border or be “concealed” (which were made visible by means of a special “reveal” button on the Prestel keypad).

By embedding cursor-control characters within the page data, it was also possible to encode simple animations by re-writing parts of the screen already displayed. These were termed “dynamic frames” and could not be created online using conventional editing terminals, but required specialist software and uploading via the “bulk update” facility. No timing options were available beyond that imposed by the available transmission speed, usually 1,200 baud download (receiving) and 75 baud upload (sending keypad entries).

The service was never as popular as it was envisaged.  Although it was taken up positively by the Travel and Financial services industries, the in-home market was never the success it could have been.  Televisions with built-in adapters were exorbitantly expensive, and hard to find, and dedicated terminals were only really affordable to businesses.

Despite this, Prestel was instrumental in developing many of the technologies we now consider commonplace on the Internet and World Wide Web today.  The Bank of Scotland had their HOBS “Home and Office Banking” service whereby you could manage your bank accounts online.  Club 403 offered online grocery shopping.  British Rail offered access to timetables.  Kays had mail order shopping from their catalogues.  There were several forums and chatlines where ordinary users could post messages and chat among themselves, and later, Micronet allowed anybody to publish their own pages, for a fairly modest fee.

Prestel was also instrumental in providing the first taste of electronic mail that many people would experience. Being able to send simple messages for free to friends and family would seem to be a novelty, but it would soon turn out to be one of the most used features of the service.  Many friendships were started and flourished through the interactions made possible via Prestel Mailbox, and Prestel was certainly responsible for more than one marriage, and perhaps the failure of several others.

Telex Link Info Sheet

Telex Link Info Sheet

To get more business users, Prestel launched Telex Link, which allowed any prestel subscriber to receive and send telex messages.  In the days before Fax machines, the telex was the official business-to-business communications medium:  Telex messages could be held to be legally binding just like a written letter.

In fact, it was only with the arrival of Micronet 800 in the mid 1980s, started as an online computer magazine by East Midlands Allied Press, and whom for a period gave away free modems for home computers with their subscriptions, that domestic usage began to rise.

This was helped by access only being a local telephone call throughout most of the country – a facility otherwise unheard of in the times before “0845” and it’s like.  Even so, Prestel subscriptions peaked at less than 100,000 subscribers – far below the “millions” of subscribers aimed for when launched.

During the daytime, when business usage was high, there was a per-minute charge to use Prestel, but in the evenings and weekends, traditionally the quiet times, it was free apart from the telephone call.

Unfortunately, with Micronet being so popular, suddenly the quiet times became fairly busy!

Prestel actually took over Micronet in 1989, and merged it with their other online offerings, forming the BT Dialcom Group.

In 1991, Prestel decided to introduce a charge during the previously free times, effectively doubling the cost of accessing the service, and within months managed to kill off the home usage almost completely, confirmed by the closure of Micronet that October.

After a decision to concentrate on core network services and not value-added services, the whole lot was sold off to a private consortium, and from there it ended up with Financial Express, where, after a brief appearance as ‘New Prestel’ it was closed down completely.

This is just a brief overview of Prestel probably one of the innovations that led to the Internet and communications systems we have today. The equipment that was used to create the Prestel service has all disappeared now it seems, not even is there any trace in any museum, unless you know better!



This entry was posted on April 22, 2013 at 6:29 am and is filed under Main (Tags: , , , , , , , , , , , , , , , , , , , , , , , , ). You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

Comments (1)

Leave a Reply (name & email required)

%d bloggers like this: