When a Mac boots up, it checks the sense pins (or on newer ones, the DDS info) to know what resolutions it can display. If it finds a display connected but off, a DDS display may be missing resolutions once it boots. If it finds no display, it won't boot.
Sometimes they boot anyway at 640x480@67Hz, but it's hit-or-miss... officially, they won't boot with nothing connected to the video port, and most of the time, that's exactly what happens.
The Xserve checks for a monitor, and if it doesn't find one, it creates a "virtual monitor" in RAM so that applications don't get weirded out.
tooki
Sometimes they boot anyway at 640x480@67Hz, but it's hit-or-miss... officially, they won't boot with nothing connected to the video port, and most of the time, that's exactly what happens.
The Xserve checks for a monitor, and if it doesn't find one, it creates a "virtual monitor" in RAM so that applications don't get weirded out.
tooki