Mark Ring Mark Killing
In addition to the ordinary mark ring that belongs to each buffer, Emacs has a single global mark ring. It records a sequence of buffers in which you have recently set the mark, so you can go back to those buffers.
Setting the mark always makes an entry on the current buffer's mark ring. If you have switched buffers since the previous mark setting, the new mark position makes an entry on the global mark ring also. The result is that the global mark ring records a sequence of buffers that you have been in, and, for each buffer, a place where you set the mark.
The command C-x C-
pop-global-mark) jumps to
the buffer and position of the latest entry in the global ring. It also
rotates the ring, so that successive uses of C-x C-
you to earlier and earlier buffers.