However, the headline feature of Windows 10 is that it is free to most existing users of Windows 7 and Windows 8 for the first 12 months, via a download from Microsoft (but don't all try to download it on Day One, okay?). As with previous versions, it comes in a variety of flavours: Home Edition, Professional Edition and so on. The retail versions will sell for the same prices as the current Windows 8.1, whilst the free download will correspond to the current installed version i.e. if you are running Home Edition 7 then you can get the upgrade to Home Edition 10. There is also a relatively low cost upgrade from Home to Professional Edition.
Windows 10 will also be available in versions suitable for use on tablets and mobile phones. However, whether most existing models are suitable for upgrading is by no means apparent.