As a tech I know you should not uninstall a older version while you are upgrading/installing to the next version, but for everyday users I did a small test to see what would happen if you did. While I was installing the 4.0 build 529 I uninstalled the 3.0 build, both version ask me to reboot, I click wait on the 4.0 one and did the auto reboot for the 3.0. It reboot and then started up normal and ask if I wanted to add devices, so I did but when I click "Use this devices" in said no drivers were found.