Hello, I just bought my iMac 27 inch 2013 Ultimo a few days ago, and when I turned it on for the first time it showed up "external disc" in the finder. Keep in mind that this iMac has no disc reader. I can right click it and eject it, but I haven't tried it yet since I don't know what it is. It also doesn't show up in disc utility. A screenshot of hard drive info What is this?