5.49 How can I start Emacs in fullscreen mode on MS-Windows?

Use the function w32-send-sys-command. For example, you can put the following in your .emacs file:

     (add-hook 'emacs-startup-hook
               (lambda () (w32-send-sys-command ?\xF030)))

To avoid the slightly distracting visual effect of Emacs starting with its default frame size and then growing to fullscreen, you can add an ‘Emacs.Geometry’ entry to the Windows registry settings. See X Resources.

To compute the correct values for width and height, first maximize the Emacs frame and then evaluate (frame-height) and (frame-width) with M-:.