Users of the most recent versions of Windows — 7 and 8 — will be given the option to upgrade for free in the first year that Windows 10 is out, and will have to buy the software after that. But those on older versions of Windows, and those made for tablets, might miss out.

Microsoft has already said that users of the home version of Windows 7 and 8 will get given Windows 10 Home for free. And users of those pro versions of those operating systems will be given the corresponding edition of Windows 10.

But Microsoft hasn’t yet said what will happen to those on Windows XP and Windows Vista. It appears that people on those systems will have to buy a new version of Windows 10 from the very beginning.

People who are building new computers from scratch will likely have to do the same, buying a new version of Windows 10 for their new computer.

And those on Windows RT, the special version of Windows 8 made for mobile devices, will also be left out. Select devices like the Surface RT and Surface 2 have been promised some kind of upgrade, but it’s unclear whether that will be a full version of Windows 10.

Microsoft is trying to get , as part of its plans for ensuring that developers can make their programs knowing what operating systems they will be used on. Microsoft is also advertising the new operating system as "Windows as a service” — not one single piece of software but a continually updated platform.

(independent.co.uk)