The prefix key C-x 5 is analogous to C-x 4. Whereas each C-x 4 command pops up a buffer in a different window in the selected frame (see Pop Up Window), the C-x 5 commands use a different frame. If an existing visible or iconified (“minimized”) frame already displays the requested buffer, that frame is raised and deiconified (“un-minimized”); otherwise, a new frame is created on the current display terminal.
The various C-x 5 commands differ in how they find or create the buffer to select:
find-file-other-frame. See Visiting.
dired-other-frame. See Dired.
mail-other-frame. It is the other-frame variant of C-x m. See Sending Mail.
find-tag-other-frame, the multiple-frame variant of M-.. See Tags.
find-file-read-only-other-frame. See Visiting.
You can control the appearance and behavior of the newly-created frames by specifying frame parameters. See Frame Parameters.