VIEWDATA

The patent name for the British Telecom Viewdata system is Prestel. A wide range of information is available on Prestel, much of which is of interest to businesses. The association of Viewdata Information Providers (AVIP) has produced a code of practice for information providers (IP's).

Videotex is a general term that includes such systems as viewdata and teletext. These two types of information system are being used increasingly in business and the home. Both use an ordinary television set to display the information. With viewdata the information is transmitted from a computer along ordinary telephone wires; with teletext it is broadcast together with conventional television programme signals sent from television transmitters.

Information is entered into the editing computer through a specialised editing keyboard. This input terminal has a QWERTY keyboard as well as numerical keys. A special button is pressed to indicate the beginning and end of a frame (screenful of information) and six other buttons are used to produce graphs and artwork. There are also keys for controlling the position of the cursor. Each frame has a 40-column display.

On Prestel the pages are numbered but one page can consist of one or more frames; these are coded alphabetically. Theoretically there is no limit to the information that can be stored and retrieved. The number of editing and storage computers can always be increased to keep pace with demand. Information that relates to a particular region and is of of local interest is stored on a computer that can only be accessed in that area.

USING PRESTEL

The Prestel user must have a television set with extra circuitry to accept Prestel (this can easily be bought or rented) which can receive instructions from the user's keypad and convert them for transmission along telephone wires. At the other end they are changed back to a digital signal so that they are understood by the computer. The reverse process happens when information is retrieved. The telephone receiver and its modem are joined to the telephone system by a jack plug so that the telephone cannot be used for making calls when Prestel is being used. A printer can be attached to the system to give hard copy when required.

The information providers supply the facts that are displayed on Prestel, assess whether or not they are marketable, and then create the frames and enter them on a editing terminal. They also maintain, improve and promote the service. Some experienced information providers have become consultants and publishers in this field taking on clients (sub IP's) for whom they produce a Prestel package.