As might be expected given the version number, the differences are relatively minor. The much lamented Start button makes a return - sort of, as it merely takes you to the Start Screen rather than a proper Start Menu. The Start Screen itself now has the ability to easily display your own choice of wallpaper as a background. The computer can now be set to boot directly to the Desktop, avoiding the Start Screen altogether. Internet Explorer moves to version 11. There are a couple of tweaks to searching, SkyDrive and in a few other areas. And that's about it.
Windows 8.1 is available as a free downloadable upgrade to existing Windows 8 users from October 17th. From the following day, it should be available on new computers on sale in stores. It's not going to set the world alight, but offers some minor improvements for those who like what Microsoft is trying to do with Windows 8.