Centrepoint Travel Software

Viewdata Explained

Viewdata is one of the several international videotex standards and was developed in the UK. The most well known viewdata service in this country was 'Prestel' (originally provided by British Telecom) but there were, and are, other private services. Private services are usually provided by organisations that wish to make information available to their customers (eg Tour Operators enable Travel Agents to make bookings interactively via viewdata).
Screens
UK Viewdata displays are the same in appearance to those seen on Teletext and have simple 'mosaic' graphics and eight colours. We have an example screen image that shows some of the display capabilities.
Terminals
A basic viewdata terminal is not unlike other computer terminals in appearance with a separate keyboard and screen - the keyboard is fairly standard but the screens do tend to be smaller than usual. Normally the screen is only capable of displaying 40 columns of text (although 80 columns is sometimes now available) which means that the characters are large and easy to read. Simple 'mosaic' graphics are available which, although only slightly better than 'block' graphics (where individual character positions can be completely blocked-in to form shapes), can be quite effective when combined with the use of several colours.
Modems
For many years the most common modem used for access to UK services used 'split speeds' for data transmission - this meant that information from the terminal to the computer could only be sent at 7/8 characters per second (fast enough for most typists) but that information from the computer could be received at 120 characters per second - fast enough to produce a reasonably quick display of a whole page of data. This type of low cost modem became known as a 'viewdata' modem and was adopted as an international standard by the CCITT (recommendation V23). Viewdata modems were often included inside videotex terminals to form a complete desk-top unit for ease of use. It is now possible to access most services via the internet or by using modems that conform to the highest international standards.
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