This section briefly describes the peculiarities of using Emacs under Mac OS with native window system support. For Mac OS X, Emacs can be built either without window system support, with X11, or with Carbon API. This section only applies to the Carbon build. For Mac OS Classic, Emacs can be built with or without Carbon API, and this section applies to either of them because they run on the native window system.
Emacs built on Mac OS X supports most of its major features except
display support of PostScript images. The following features of Emacs
are not supported on Mac OS Classic: unexec (dump-emacs),
asynchronous subprocesses (start-process), and networking
(open-network-stream). As a result, packages such as Gnus,
GUD, and Comint do not work. Synchronous subprocesses
(call-process) are supported on non-Carbon build, but
specially-crafted external programs are needed. Since external
programs to handle commands such as print-buffer and
diff are not available on Mac OS Classic, they are not
supported. Non-Carbon build on Mac OS Classic does not support some
features such as file dialogs, drag-and-drop, and Unicode menus.