Windows 10 release date: new Microsoft operating system to arrive at end of July

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

Terry Myerson silhouetted against the backdrop at the Windows 10 launch event (Microsoft)

Microsoft will release Windows 10, a huge upgrade to its operating system, 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".

Microsoft is giving away Windows 10 for free apparently to reduce "fragmentation", the challenges for developers who at the moment must make software to work on a variety of operating systems. It also brings it in line with competitors like Apple, which has given away the most recent versions of its own desktop operating system.

The company said that those "who want to be among the first in line for the free Windows 10 upgrade can reserve a free copy in the coming weeks". To do so, an icon will come up in the system tray at the bottom right hand corner of the screen — clicking on it will bring up the reservation process.

It will be released in 190 markets, the company said.