Windows only natively supports installing the Enterprise Edition of Win-8 to USB devices, which is easy to do with the Windows To Go Creator Wizard from inside a Win-8 Enterprise install, or with some command line tech-work from any version of Windows-8.
TechNet - Windows-To-Go Step by Step.
We can however with a little workaround get any version of Windows-8 to boot and run from a USB/SD flash device. It requires that we first install Windows-8 in a particular way to a standard SATA hard drive, then we just have to clone that to our USB/SD flash device.
The tutorial on this page totally depends on possessing a correctly configured hard drive that we will use to create our Win-8 bootable USB/SD flash device, so if you do not already have that to hand then you need to start with this page. The other items required are of course a suitable USB/SD stick or card, plus a cloning tool that can correctly do what's needed. If you want a decent performing system then you will need to use a good quality device that has decent read/write speeds. Our recommend tool for the cloning operation is Partition Wizard, which is currently free for home use.
A Few Provisions.
While we have shown that it is possible to get any version of Win-8/8.1 booting from a USB/SD stick or card, we cannot testify to how viable it may be in the long term. It has merely been a proof of concept project for us and although we can foresee no issues with activating Windows and applying updates, we have not yet seriously explored this. For anything more than just the testing of Win-8, or the occasional use for access, or diagnostics, or the running of an app, then please refer to the further information boxes below to understand some of the factors that will affect usability.
Once you have all the required components ready then fire up Partition Wizard. In our example in fig:1 we are running it from Windows 7 on the machine we are using. You could however run it from a bootdisk if that was more convenient or if your circumstances require it, (links and details for the bootdisk version here).
This is the final button you will have to click to start the cloning operation. Depending on the write speed of your flash device that could take up to an hour, so the advice given here may be pertinent, but not crucial in this situation because if the write fails you can simply try again.
If you are not immediately taken to the progress box shown next in fig:11 but instead get a message that Partition Wizard needs to reboot to complete the operations, then it should be safe to allow this, but we would prefer to cancel out of everything and use the Windows Disk Management Utility to remove drive letters from both the donor and target devices, then start over.
A short video showing the Disk Copy Wizard being used can be seen here.