The free upgrade applies to all systems currently running Windows 7, Windows 8 or Windows 8.1, and mobile devices running Windows Phone 8.1. There is a caveat though: the free download of Windows 10 to upgrade Windows 7, Windows 8 or Windows 8.1 systems is only applicable for 12 months from the date Windows 10 is made generally available and officially launched the coming summer. Windows 7 and Windows 8 systems must be installed and upgraded with latest hotfixes, updates and service packs, which in case, SP1 for Windows 7 and Windows 8.1 for Windows 8.
Unfortunately, if you have a Windows RT or Windows RT 8.1 (i.e. Surface and Surface 2) devices, they are not getting the full Windows 10 update. Instead, Microsoft is working on an update for Surface and Surface 2 which will have some of the functionality of Windows 10.
In addition, the terms and conditions of Windows 10 Free Upgrade Offer also exclude editions meant for enterprise from free upgrade, including Windows 7 Enterprise, Windows 8 Enterprise and 8.1 Enterprise. For smartphones and mobile devices, the availability of the Windows Phone upgrade may vary by OEM, mobile operator, or carrier.
Good news is that, Microsoft is allowing almost everyone with a qualified PCs to upgrade to Windows 10, regardless of whether the current Windows OS installed is genuinely licensed or pirated. It means that even if your copy of Windows 7 or Windows 8.1 is activated with a loader, activator, toolkit or KMS with leaked product key, you’re still able to upgrade to Windows 10. It’s likely that unactivated Windows 7 and Windows 8.1 will also able to upgrade to Windows 10.
The reason almost everyone can upgrade to Windows 10 is simple. That’s because Windows 10 will be delivered via Windows Update or ISO images to all qualified computers, WITHOUT a genuine product key for Windows 10, which Microsoft doesn’t plan to giveaway. And, Microsoft has given up on genuine license validation years ago. Without validation to verify that the installed Windows is genuine, everybody gets Windows 10 update for free. That’s explain why Microsoft specified that a non-genuine system will stay as non-genuine and illegitimate after upgrading to Windows 10, as there is still no way to legitimately activate the PC. In addition, with the public availability of ISO images download and no radical change of anti-piracy method in Windows 10, it’s likely the the similar cracks could be continued to use to pirate Windows 10.
Windows 10 marks the official positioning of “Windows as a service”, where Microsoft will update the Windows product for the lifetime of the device on which it’s installed. The trend actually started in Windows 8.1, where all Windows 8 users can upgrade to Windows 8.1 for free. This is contrary to previous practice where users will to pay to buy new major version of Windows operating system, and ensure that the Windows is always up-to-date.
One thing to note is that Windows 10 has two separate branches, namely Windows 10 for Desktop for PC and hybrid tablet including desktop, laptop, Surface, and other OEM hybrid and tablet devices; and in the continuity of Microsoft’s tradition in confusing and undecided naming, Windows 10 for Mobile, for phones and small tablets under 8 inches in screen size will succeed Windows Phone 8.1, with support for ARM as well as Intel x86 system-on-chips. As the result, Windows 10 will unify the traditional desktop Windows platform with Windows Phone platform.
Update 2: Official Windows 10 free upgrade offer has ended, but you can still use a loophole to upgrade to Windows 10 for free.
Update 1: Reserve Free Windows 10 Upgrade