Rosin core predates that computer by a half century, at least. Kester was formed in 1899 just for that purpose, according to them. Was just looking at Allied Radio 1933 and rosin core solder is prominent. Not sure why the comments; radio building was at high form in the early 20th century.
Thanks for that pointer, all I could find was a vague wikipedia article. Obviously soldering was well established. The specifics of what was available weren't clear.
