Can you set up windows on iMac on a separate drive ?

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I've read you can set up windows to run on an iMac on a partition on the hard drive, but can you set it up so the windows is on an external drive to boot from rather than the internal drive ?

Reason for asking (and hopefully making sense) is daughters fella has a new force feedback steering wheel and when they come to visit, he wants to bring it down and we can have a go on a few driving simulators he has, but these run on windows and also the wheel won't run properly on an iMac (don't get force feedback etc).

I know the simple route is set windows up on the main drive, but I don't really like using windows and would prefer the option that I can then just unplug the external drive and windows is no more on my iMac :D

Anyone know if it can be done ?