In the setup process for a new virtual machine, VirtualBox presents several different OS types and versions to choose from:
I'm curious as to what VirtualBox actually does when you select an OS. I'm sure, for example, that it wouldn't present the same hardware to a Windows 3.1 guest as it would to Windows 7. What I'm less clear on, however, are the potential differences between, say, a Linux and a BSD guest: if they're both designed to run on the same hardware, then what optimizations could VirtualBox possibly make if it knows which OS it's hosting?
In other words, what types of changes does VirtualBox make to the VM when you select an OS?