hardware detection at boot time

[Doofus <doofus@bulldoghome.com>]

The boot process appears to run some kind of hardware detection at two 
stages. The first one begins with a line like:

   "Detecting hardware: agpgart i810-tco yenta_socket 3c59x piix 
i810_audio usb-uhci"

and will load any modules for these if they're present and if the code 
isn't built into the kernel.


Then slightly later in the process there's another round of efforts to 
load modules. in which you unsurprising get "already loaded" messages. 
Why is this? It appears to me that the second effort is done by the 
hotplug code, which presumably can be controlled by the scripts in 
/etc/hotplug. But what is it that causes the first set of hardware 
detection? Could someone please very briefly explain how this works and 
correct me if my understanding is askew?