How to Run a Portable Version of Windows from a USB Drive

http://lifehacker.com/how-to-run-a-portable-version-of-windows-from-a-usb-dri-1565509124

Mac users have had this ability for ages when you can boot from an external drive connected via the Firewire port with latter support for USB- or Thunderbolt-connected drives. The reason being the Mac computers are homogeneous being made by one and only one company -- Apple itself. Therefore, the operating system has all the drivers it needs to run on all Mac computers within a reasonable linage. I assume that it works with Window 8 now because of tighter control of the driver ecosystem that Microsoft forces hardware manufacturers to comply. Therefore, all newer PCs will be Windows 8 compatible and the drivers for the motherboard are already included in Windows 8 itself. No need to hunt for drivers. In effect, Windows has adopted the homogeneous nature of Apple.

Clearly the advantage of running Windows (or Mac OSX) from an external drive is mobility and security. Once the external drive is disconnected from the computer, there is no trace of it on the computer. This way, you can carry your Windows 8 without without having to carry the bulky computer. If your friend has a machine that supports Windows 8 and can boot from the USB port, then you just simply plug in the external drive with Windows 8 in it , and boot from it.

Given that there will be a lot of write operations happening while Windows 8 is being used, it's best to use USB3 and an SSD drive.