How they did/can we do this old printer effect?
I'm speaking about those little dots.
You can do it in photoshop under filters>pixelate>color halftone
Google tutorials for how to use settings
>How did they do it
Some of them used dot matrix printers, some of them used serigraphy.
In both cases it was caused by every colour being printed separately (hard to avoid with dot matrix printing, avoided in serigraphy by having precise alignment, which cheaply printed magazines didn't have).
Also some are still doing it (I'm looking at you Panini and I don't like what I'm seeing)