Oh i also didn't know this a week ago; my old video card knowledge belongs into a museum. SBA or Side Band Addressing is a special AGP feature more or less important for the video accelaration. I'm still looking for a good technical website to learn a bit more about that and related fields. Some people are arguing SBA is risky to run, other are saying the accellaration effect is minimal.
The good ancient computer times, and the people were satisfied also without any agp stuff and earsplitting fan din. ;-)