Windows 10 will be offered as a free download to users running any version of Windows 7 or 8 - but what about those on XP, Vista, and other operating systems?
Microsoft has revealed another way to get the software for free, confirming that anyone who downloads the latest preview build will get the final version without cost.
Users must sign up for the Windows Insider programme to take part in the trial, but that's the only caveat.
"As long as you are running an Insider Preview build and connected with the MSA (Microsoft Account) you used to register, you will receive the Windows 10 final release build and remain activated," Microsoft's Gabe Aul wrote on Twitter.
Offering Windows 10 upgrades to preview users also gives those running a pirated version of Windows the chance to upgrade to a legitimate copy free of charge.
Windows 10 will be available to download on July 29. Users must install it within the first year to take advantage of the free update.
Windows 10: Everything you need to know about Microsoft's seamless OS
Watch a video introducing Windows 10 below:
