Just a heads-up regarding Windows 7 support.
The Calibre Windows download pages states:
If you are using Windows 7 or Vista please, use calibre 3.48, which works with all Windows 7/Vista machines, from here. Simply un-install calibre and install 3.48, doing so will not affect your books/settings.
However, one can install up to version 4.32 under Windows 7.
https://download.calibre-ebook.com/4.html
Thank you, kovidgoyal for providing the reasons why Windows 7 is not supported in version 5. Like others in this post I first thought it was due to a non-technical policy.