Understanding initialization

[brianjd]

I am trying to grasp a low-level understanding of the hardware
initialization in the boot process.  When the PC first powers up, the
processor is able to access CMOS.  On some typical PC
architecture diagrams I have seen, the processor has to traverse the
North and South Bridge to access CMOS and the Flash BIOS.  How can it
do this without initializing these bridges?  What keeps me from
communicating directly with a USB port without bridge initialization?

Thanks,
-- Brian Deep