Supermicros (and to a similar degree Tyan) are mostly in the "server class"
of motherboards. That apparently means they put a *lot* of self-test code
in there somewhere. I've had literally thousands of Supermicro machines of
a dozen different types at various times, and they all took an inordinate
amount of time to decide to think about booting no matter what (all
auto-detect turned off, quickboot on, inboard SCSI disabled). I got used
to it, because quality-wise it was worth the wait.