Left: William Gallagher talks to Breakfast host Susanna Reid about his time at Ceefax
It took some time to build up to 22 million readers. Originally BBC technicians devised the service to provide subtitles and to use the spare capacity on a TV signal. Back in the analogue days, if you tuned your TV poorly you could see a couple of lines at the top of the picture that looked like fireflies racing about. Ceefax used those non-picture lines to transmit all of its pages.
Ceefax was officially launched in 1974 when a TV set capable of receiving it would've cost you £700 - or over £6,500 in today's money. By 1976 it was estimated that there were 6,000 TV sets in the country that could show Ceefax but by 1985 it was 10 million. By the 90s it was next to impossible to buy a TV set that didn't feature it.
Over that same time, the service grew internally, too. At launch, there was one journalist who updated all the pages every now and again, at least within 9-5 office hours. But it became a round-the-clock service that's updated when anything happens. Throughout its life, Ceefax was very focused on news - but it did always include entertainment, too.
The average web page today is about 100k in size where every Ceefax page was 1k but within that tiny space there were games, interviews, reviews - and subtitles. Where you now see every TV programme including a website address and most have a Red Button prompt, you used to see the page number 888.
That got you subtitles for dramas, entertainment and even for live news.
The subtitles were obviously done by humans: there were mistakes. But mistakes were remarkably few and what ones there were gave the service a personality.
Sections of the service had fans who to this day remember the TV reviews of Caroline Jack, even though - sorry to spoil this so many years later - she never existed. Originally she was written by whoever was on duty that day. For a long time she was written by one person. Hello.
If every page had tight word limits, there were also limits to the number of pages. It was a big deal to get a new section on and I got a DVD column launched on there. It sounds daft now since I couldn't play any clips, couldn't show any images and there wasn't enough room for interviewing people, but it was an experiment that seemed to work.
One thing that could not afford to be an experiment and that really could not afford to fail was the National Lottery. If you were on duty on Wednesdays or Saturdays, you had to get those numbers live on screen as fast as humanly possible. It was never fast enough: one woman used to phone to complain every week. Once she complained that the numbers were up too quickly. Ceefax had fans who paid that much attention.
Unfortunately, some of them thought they'd won the lottery. There was one time - I wasn't there, I promise - when the numbers were wrong. It was corrected extremely quickly, but still people noticed and thought they had won.
That was when the lottery was new and when you couldn't just get the results online.
The internet may have delivered the killing blow to Ceefax but the service was damaged as soon as digital satellite and cable TV came in: soon, instead of getting Ceefax just by pressing a button, you had to switch off digital and return to analogue.
But there was still one place everyone could see Ceefax without switching off anything: BBC2 has regularly run hours upon hours of what it calls "Ceefax in view" where pages are shown one after another. Rather than using the spare lines of the TV picture, the Ceefax pages became the picture.
Ceefax in view pages were always accompanied by music, too. You may struggle to understand how such a small service as Ceefax meant so much to so many, but the fact that the music had its fans, too, has bemused even Ceefax staff.
William Gallagher was a BBC Ceefax journalist until 2004. To this day, he says he gets emails and tweets from readers about the DVD column he launched there.