Is it possible to use multiple desktop environments on same system?

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http://askubuntu.com – I am using Ubuntu 12.04. I want to try out KDE and other desktop environments. But I'm not sure if I'll like them enough to switch permanently. I want to be safe and make a transition in a piecemeal fashion. Is it possible to install KDE on Ubuntu and yet not do away with the default Unity shell? Could I install multiple desktop environments and switch between them by tweaking some startup configuration and then rebooting? (HowTos)