open up
/etc/X11/xorg.conf
you will see a section that looks somewhat similiar to this :
Code:
Section "Screen"
Identifier "Screen 1"
Device "Standard VGA"
Monitor "My Monitor"
DefaultDepth 16
Subsection "Display"
Depth 8
Modes "1280x1024" "1024x768" "800x600" "640x480"
ViewPort 0 0
EndSubsection
Subsection "Display"
Depth 16
Modes "1280x1024" "1024x768"
ViewPort 0 0
EndSubsection
Subsection "Display"
Depth 24
Modes "1280x1024" "1024x768" "800x600" "640x480"
ViewPort 0 0
EndSubsection
EndSection
now as you can see towards the top the "default depth" is "16", so the
only section out of all that, that will be used is the following because
as you see the depth is 16 for this section and that is default :
Code:
Subsection "Display"
Depth 16
Modes "1280x1024" "1024x768"
ViewPort 0 0
EndSubsection
now when you look at the modes line you see that the first one
listed is 1280x1024, meaning that this is the resolution it will
load up to... so if you want 640x480 to be used, then put it
as the first option in modes ...