Ediff maintains a registry of all its invocations that are still active. This feature is very convenient for switching among active Ediff sessions or for quickly restarting a suspended Ediff session.
The focal point of this activity is a buffer called *Ediff Registry*. You can display this buffer by typing R in any Ediff Control Buffer or Session Group Buffer (see Session Groups), or by typing M-x eregistry into the Minibuffer. The latter would be the fastest way to bring up the registry buffer if no control or group buffer is displayed in any of the visible Emacs windows. If you are in a habit of running multiple long Ediff sessions and often need to suspend, resume, or switch between them, it may be a good idea to have the registry buffer permanently displayed in a separate, dedicated window.
The registry buffer has several convenient key bindings. For instance, clicking mouse button 2 or typing RET or v over any session record resumes that session. Session records in the registry buffer provide a fairly complete description of each session, so it is usually easy to identify the right session to resume.
Other useful commands are bound to SPC (next registry record) and DEL (previous registry record). There are other commands as well, but you don't need to memorize them, since they are listed at the top of the registry buffer.