I have been searching and trying to figure this out, but have had zero luck. What determines the primary boot screen? What I mean is, on the mini, I have the HDMI and Thunderbolt port. What factors make the computer decide which one to show the grey Apple boot screen before the OS loads? If I boot the computer and then power on my monitors, it defaults to the HDMI. However, if I **** down, reboot, or power on if the monitors had been left on since last boot, the boot defaults to the Thunderbolt port. This is driving me mad! On my old 2009 mini, the Mini DVI was always the default boot. On my 2011, it can't seem to make up its mind. Any ideas?