Microsoft made waves when it announced that Windows 10 would be available as a free upgrade - but it isn't quite as simple as that.
Here we have explained exactly who can upgrade for free, and under what circumstances you will have to pay for it.
Updating pirated windows xp
Over a decade old and no longer a supported platform, Windows XP cannot be upgraded to Windows 10.
Users of machines running either XP or Windows Vista must perform a clean install of Windows 10 - and there are no discounts or free offers either; you will have to pay the full price.
After initially saying anyone running a pirated copy of Windows 7, 8 and 8.1 would get a free, licensed upgrade to Windows 10, Microsoft has backed up slightly.
Pirates will still be allowed to update their machines to Windows 10, but they won't get it for free.
Windows Phone 8.1 users will also get a free upgrade to Windows 10 Mobile.
However, anyone running Windows Enterprise and Windows RT will not be eligible for the upgrade.
Those who do update their operating system will get full support from Microsoft until the end of mainstream support in October 2020. The free upgrade is only available for one year after Windows 10 is released on 29 July.
Anyone who doesn't update in the next 12 months will likely have to pay the full price - between £80 and £140 depending on which version you opt for.
Instead, Microsoft says it is "planning very attractive Windows 10 upgrade offers for [hardware partners] customers running one of their older devices in a Non-Genuine [pirated] state."Recognising that some Windows users are running pirated copies without realising it, Microsoft said: "Many customers are unwitting victims of piracy, and with Windows 10, we would like all of our customers to move forward with us together."Insiders, the name Microsoft gives to its beta testers, will also receive a free upgrade to Windows 10.
Already running beta builds of the new software, Insiders will be upgraded to the final RTM (release to manufacturing) copy once it goes on sale.
Updating to this copy will not require a clean install.