Microsoft has revealed that Windows 10 will bring its voice-controlled assistant Cortana to PCs. <br /> <br />It also unveiled a headset that it said would one day project the operating system over views of the real world. <br /> <br />In addition, the firm announced that the OS upgrade would be offered free of charge for devices running Windows 8, Windows 7 and Windows Phone. <br /> <br />The offer, which is limited to the Windows 10's first year of release, may aid its adoption. <br /> <br />It marks a change in strategy from Microsoft's previous policy of charging for major updates, and could help avoid a repeat of the relatively slow uptake of Windows 8.
