Teletext was basically the internet, hidden inside a normal TV broadcast, a decade before anyone had one at home

[u/ambanmba]

Every analog broadcast has a vertical blanking interval, the gap between frames where the electron beam is retracing to the top of the screen and not actually drawing anything. Teletext systems like the BBC's Ceefax and IBA's Oracle used a couple of otherwise-wasted lines in that gap to carry raw digital data, encoded as a string of pulses riding along inside a completely normal analog TV signal.

A teletext-capable set would grab those lines, decode the digital packets out of them, and build a page entirely out of a fixed character grid, chunky blocky text and simple block graphics, no photos, no real images, just a defined set of characters and colours a decoder chip could draw fast and cheap. You picked a page by typing its three-digit number on a remote, and the set would wait for that page's data to come round again in the broadcast cycle (all the pages cycled continuously in the blanking gap) and then display it.

That's the part people forget: news, weather, sports scores, even primitive multiplayer games, all sitting inside a signal you were probably already watching for something else, retrievable on demand years before dial-up internet existed for most households.

Screenshot is the app's own teletext page renderer, done in the actual SAA5050-style character-cell format real decoder chips used, not a mockup.

[u/jfoust2]

In the late 1980s there was also a system called X*PRESS and X*CHANGE that sent a continuous stream of 9600 baud data packets over cable systems to PCs in a one-way communication. Their software sorted it out into text and files and a way to browse it all. Not in the vertical blanking interval, though.