Loading of Assemblies

When an ASP.NET Application first starts, an application pool is created and
assemblies loaded into it.

How does ASP.NET "know" which assemblies to load - initially - into that
application pool? What controls which assemblies are initially loaded? Is it
Machine.config + App.config? Is there some other way that ASP.NET knows
which assemblies to load... any "hard-coded" that always load no matter
what?

When does ASP.NET load 3rd party assemblies into the default application
pool. For example, say that I have a 3rd party component (some UI widget) on
a page. When is that 3rd party component's containing assembly loaded?


Thanks.