If a reference already has a link that Just Works, such as the one replaced by https://en.wikipedia.org/w/index.php?title=Berkeley_Software_Distribution&type=revision&diff=931316151&oldid=930383832, without any requirement to register (much less a "sorry, you can only borrow this for 14 days, and if somebody already has it checked out, you'll have to wait until they're done with it" limitation), *please* don't replace it. The Internet Archive is not inherently a better site than other sites providing documents.