The latest version of the operating system, which skipped straight from 8 to 10, will be offered as a free upgrade to many current software users, Microsoft announced.
The offer is available to those running Windows 8, Windows 7 and Windows Phone on their devices, but it is limited to the first year of the OS’s release.
Compared to previous policy changes, the shift in strategy could be a bid to encourage interest in its products after the slow uptake of Windows 8 – regarded by some as “too touch-centric”.
The computer giant unveiled the Windows 10 computer preview on Wednesday at the firm's Redmond headquarters, showcasing many new features.
Joe Belfiore, corporate vice president at Microsoft, announced that Cortana, the voice-controlled digital assistant, will now run on PCs and not only Windows Phone handsets.
Belfiore explained how Cortana can bring up presentations, locate photos taken at a specific time, and send emails when asked to.
Windows 10 brings the same operating system to devices of all sizes as part of a new vision that gives the user a mobility of experience from device to device.