Installed to external disk but still lost storage space

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."

 

You can check the size of the .PVM file and let us know it size. The size of the PVM file will be based on the Windows edition installed.

 

At the time of writing, the .PVM is 39.83 GB. I have done some downloads on Windows 10 though. When I downloaded it, I believe it was only 19 GB. It's Windows 10 Education. However, like I said I installed to an external disk, so that's where the .PVM is located. I wouldn't expect that to be contributing to filling up my hard drive.