Install Windows 7 on external drive and boot it from a Mac I want to install Windows 7 on an external hard drive, and boot from it when needed. 

Is this possible on a Mac? I have heard from some sources that it is not possible to boot Windows from external drives, at least on the new Macs. I found this quite surprising. 

Any idea if this is true?
It is possible, but it's not straight forward. This detailed step by step guide (which I did) contains all you need to know to install and run Windows 7 or 8 from an external drive (USB3 or thunderbolt): http://bleeptobleep.blogspot.fr/2013/02/mac-install-windows-7-or-8-on-external.html

To sum up, this guide will help you:


Get the Windows installation pack from a DVD or ISO file
Partition and format your external drive to make it bootable
Deploy Windows on your external drive
Boot on your external drive
Install Windows
Download and install the bootcamp drivers (without even using the bootcamp assistant)