If I use PC-BSD with the default shell (Korn) then Ctrl+r doesn't work. Why won't it work?Ctrl-r was introduced to search your history in the late 1970s or early 80s and my BSD still can't do it (while Ubuntu can).Ctrl-r  originates with Emacs doesn't it? When? 1975? 1983? 
Why can't Korn Shell do ctrl-r?
ksh;command history;history;line editor;pc bsd
Ctrl+R works with ksh in emacs mode (ksh -o emacs or set -o emacs within ksh), and it was most probably the first shell to support it. Only it's not as interactive as in zsh or bash or tcsh's i-search-back widget.In ksh (both ksh88 and ksh93), you type Ctrl+RtextReturn. And Ctrl+RReturn to search again with the same text.In vi mode, you can use ? to search backward and n for next search.That emacs incremental search feature was added to:bash/readline at least since July 1989 as the feature was already mentioned on usenet at that time but probably not from the start as the version of readline shipped with zsh-1.0 didn't have it.zsh since 2.0 in 1991 after the line editor was rewritten and no longer used readline.tcsh in V6.00.03, 10/21/91, but not bound by default (tcsh had other search mechanism on Meta-P for a while before that though).ksh: ksh was most probably the first Unix shell to have an emacs editing mode, written in 1982 by Mike Veach (as well as the vi mode by Pat Sullivan, reusing code that those two had already applied independently to the Bourne shell) at AT&T. ksh was first introduced outside AT&T at the 1983 USENIX conference where those features were described, but was not commercially available until some time after that (1, 2). It's hard to tell if ^R was already there at the time (in any case, it was already there in 1986), but it's hard to imagine it wasn't as it's an essential feature, especially for a shell, and I'd expect vi mode's ? would also have been there at the time.