If I "erase and install" Ubuntu in Parallels on OS X, will it also erase the files on my iMac?

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http://askubuntu.com – I downloaded Ubuntu 12.04, ran Parallels Desktop, then booted the Ubuntu ISO. I chose to install and that led me to this window i'm now in, asking me about Installation Type: Erase disk and install Ubuntu, or Create/resize partitions for Ubuntu. I'm not sure if I need to partition; but if I choose to erase disk and install, I worry if I'll erase my iMac files with it. I'm asking this here because I haven't seen or read any walkthroughs on this that showed that screen about erasing everything before installing.Do I erase and install? Or alternatively, what will happen if I just go on and "try (HowTos)