Free upgrade will be shipped to Windows 7 and Windows 8.1 users on July 29

The upgrade will be offered free to users running Windows 7 and Windows 8.1. The free offer will be available for the first year after it is released.

For users on older versions of Windows, Microsoft hasn't yet said exactly how upgrades will work. It's thought that those on Windows XP and Vista will have to buy new versions of the operating system, as will those building their own computers.

Microsoft announced the new operating system late last year, before unveiling new features in January. But it had previously stayed quiet on when exactly it would come out, only teasing "later this year".

The new Windows brings back the Start bar, as well as a range of other features. It is widely seen as an attempt to recover some of the damage done by Windows 8, which was largely criticised by users.

It also marks the beginning of "Windows as a service" — the idea that the operating system is not just one product but a continually updated one that works across devices. Microsoft said in its announcement that "once a Windows device is upgraded to Windows 10, Microsoft will continue to keep it current for the supported lifetime of the device — at no cost".