You don't really notice it that much. There's computer like stuff, like the positronic brains! They're just not real computers. I think he was writing in the 40s so. I didn't really notice until I read the Foundation sequels he wrote later in life, because he mentioned that the computer revolution had made the older books sort of laughably out of date, and he tried to correct it. Without actually going back and rewriting them, 'cause that's lame.