I just installed Windows 10 Education using Parallels from an iso. Before downloading Parallels and the iso for windows and installing windows, I had about 20 GB left on my hard drive. Hence the install to an external disk during Parallels setup. Now however I just checked my storage and I only have just over 3 GB left. What's taking up all that storage? I'm pretty sure the category "Other" in my storage management has ballooned. It's 43 GB and I don't think it was anywhere near that before. But, I don't know what "Other" is. One thing that may be contributing to this is the fact that on my unreliable connection I had to try to download the iso 3 times, with varying degrees of completion until it worked. But that's a mystery to me as well because that download is about 5 GB and as soon as I finally got it the iso file showed only a few kilobytes under "get info."