When Windows 8 first appeared, Microsoft broke from their past sales strategies and provided no boxed retail versions of the operating system. They had downloads for upgrading from earlier Windows operating systems, OEM versions, and a System Builder edition that essentially worked as a retail version for individuals making their own pc’s. With the upcoming 8.1 refresh, they are returning to the older paradigm and will have retail versions of this system available.
If you are currently using Windows 8, the 8.1 update will cost you nothing more than the time to download and install it. If you are not using Windows 8, then you will have some issues trying to upgrade. You will no longer be able to upgrade from Windows 7 and retain your installed programs. All of your desktop applications will need to be reinstalled. Your data files will remain intact however.
It will not be possible to do an upgrade from Windows XP or Vista straight to Windows 8.1. Microsoft advises you to buy the full retail disc and do a clean install from it.
Starting October 18th, Windows 8.1 and Windows 8.1 Pro will be available as downloads or in boxed, retail editions containing the necessary dvds to install. The price for the full versions will be $119.99 for Windows 8.1 and $199.99 for Windows 8.1 Pro.
You can read more at the Windows Blog.