I installed auctex from Ubuntu's software center, and then I installed a newer version of auctex from emacs.

I then uninstalled the auctex installed by Ubuntu's software center. I found that it didn't uninstall the one I installed from emacs. 

How does emacs manage its packages?

Are there no interference between emacs and Ubuntu in managing installation and uninstallation of emacs packages?

If I am correct, a few years ago, there was no way to install packages within emacs?

Thanks.