Goes even back as far as (at least) the 80s. We had a School Trip and watched a Bud Spencer/Terence Hill Movie on the Cinema Canvas in the Auditorium. So apparently there were already means of connecting a Projector with an AV source, 'Beamers' aren't that new of a concept.
Before that, there was something they called "Super 8". Primarily used for Amateur Filming but you could also rent (sometimes shortened) reels of TV series Episodes or the like until the use of Videotape became common and affordable.
Super 8 film - Wikipedia