Can I Install Windows 10 in a extarnal hardrive on my mac?

Apple's Boot Camp only allows for a partition on your internal SSD. Virtual Machine solutions (e.g. Virtualbox, Parallels, and vmware) may allow you to put the Windows 10 guest on an external drive. I am using the free Virtualbox, and have Windows 10 running on an external drive. Ideally, that external drive would be an SSD device. Allocate no less than 50 GB for that guest drive size. Considerably more if supporting larger applications such as MS Office, etc.

The Windows 10 Fall Creator's update is around 7GB compressed, and auto update will download it over and over and ... each time creating a new 7GB file. I had to disable auto-update, cleanup the system files (21GB), and perform a manual installation of the Fall Creators update to finally get it installed. It is a PITA.

Parallels will let you put your windows virtual disk on an external drive. I think there are versions of Windows that you can boot from an external drive. OEM version? Professional version? It's a silly Microsoft restriction.

R

Windows itself doesn't allow for the installation on an external drive, unless you're using the Enterprise edition.

Windows users have a fair number of tools that get past this restriction for the Home editions. It may be risky to try and use them from a Mac.