OS X server installation on Mavericks question..

Does installing OS X server onto a machine running OS X Mavericks run as an 'add-on', or is it it's own separate OS that wipes OS X Mavericks? I only have the one Mac right now so obviously don't want to lose everything by installing server onto it, as server isn't needed I'm just doing it as a useful extra and for fun..

Thanks for any help!