Towards the end of 1974, the BBC television service in the UK began experimental test broadcasts of Ceefax. Ceefax was first developed by the BBC in 1972 as a text based information service, which was encoded into the vertical blanking interval of the standard analogue TV signal. The generic name for Ceefax is of course teletext.
Originally it was intended to provide a subtitling service for the hard of hearing, but it was soon realised that it could provide a multi-page “magazine” of news and other information.
All this was achieved before the time that 8-bit microcontrollers appeared on the market, so it was done with help of minicomputers and custom hardware.
The video below is a colour public information film produced by the BBC in the early summer of 1975 to announce the new service. Part 2 follows later.
Teletext produced a colour text and block graphics display of 40 characters wide by 24 lines. It used 3 bits for the colour, to give 6 colours plus black and white.
Wikipedia has more technical information here:
The experiments at the BBC would almost certainly be done on a minicomputer, with custom created equipment to insert the teletext into the video signal.
In one shot of the Ceefax control room there is an ASR33 teletype.
A paper tape of the page contents was produced in the editorial office and then rushed down 2 floors of Television Centre, so that it could be loaded into the “core store” in the Central Apparatus Room.
This article from 2012 describes some of the history of Ceefax at the BBC.
This one provides a slightly different technical perspective.
As a 21 year old electronic engineer, straight out of university I joined BBC Research Department, some 11 years after this film was made. Some of my departmental colleagues appear in the film.
The BBC disbanded their Ceefax service in 2012 - 40 years after its inception.