About gdm3

Hello
With my i386 wheezy desktop I had the surprise of gdm3 display
manager, whereby now the X server is started automatically, without

startx

gnome-session.


 How should I manage not to have the same situation with one of my
cpu-gpu servers? It  is usually used for chemical computations from
the console, while there is also a dormant X server to be used
occasionally with a gpu-enabled graphic program. The X server has not
to be started in order that the cpu-gpu calculation can be run.

thanks

francesco pietra