Before version control was popular, what did large companies do?

I was introduce to version control around 2003 (svn) and before that at small companies we would just ftp files around because we all worked on separate parts of the codebase. I didn't work at a large company (IBM, Microsoft, etc) but I'm really curious how companies with that many developers handled source control and conflicts before the likes of git and git[hub|lab] etc.