Viewdata is one of the several international
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).
UK Viewdata displays are the same in appearance to those seen on Teletext and
have simple 'mosaic' graphics and eight colours. We have an
image that shows some of the display capabilities.
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.
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
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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