Windows 10 upgrade information - 6 more months to upgrade for free -

Eligible Windows 7, 8.1 and Phone 8.1 customers can upgrade to Windows 10 for free in the first year after the release of the new operating system. Eligible meaning customers with genuine licenses. While others may upgrade as well, their systems won't be genuine after the upgrade.

The Windows 10 edition that customers can upgrade to for free depends on the operating system that is upgraded. Windows 7 Home Basic, Home Premium and Windows 8.1 systems are upgraded to Windows 10 while Windows 7 Pro and Ultimate, and Windows 8.1 Pro systems are upgraded to Windows 10 Pro.

Customers who have upgraded to Windows 10 in the first year won't be charged after the 12 month period. "Once a customer upgrades, they will continue to receive ongoing Windows innovation and security updates for free, for the supported lifetime of that device". This indicates that the license is tied to the device the upgrade is run on.

MS will charge for Windows 10 after the twelve month period in which the operating system is available for free and also through retail channels. This won't affect customers who used the free offer to upgrade but customers who don't have an eligible license (for instance Vista and XP systems) and new customers.