You can now create a Windows 8.1 image stored and run on a USB device.
Here’s how to set it up. From the Control Panel select “Windows To Go”:
Insert your USB key:
Select the Windows ISO image:
Enter a BitLocker password:
In the Choose a boot option screen, select a boot (startup) option. If you tap or click Yes, the Windows Boot Manager configuration will be modified to automatically boot from your Windows To Go device when it is connected to this host computer:
NOTE If you want to change the boot option after running the wizard, in the Windows 8 Start screen, type Change Windows To Go Startup Options, tap or click Settings to change the search scope, and then tap or click the Change Windows To Go Startup Options app to open it.
When provisioning is complete, tap or click Save and restart to restart the host computer:
Full instructions can be found here: http://www.microsoft.com/en-us/download/details.aspx?id=36184