@WinHEC today Microsoft has showed all of the update paths for Windows 10. This Upgrade Matrix shows if you can go directly to Windows 10 or not. There is a few interresting things in this overview.
As expected there will be no upgrade to Windows 10 for Windows RT. This is another reminder that the RT Plattform is not going to be kept alive in the future.
For Windows 7 SP1 and Windows 8.1 S14 (Update 1) it will be possible to upgrade directly from Windows Update. For all other supported scenarios you need to to an step by step upgrade or use an ISO media to perform the upgrade.
As a side note it will also be possible for computers running pirated versions of Windows. Microsoft’s Terry Myerson has announced that the software vendor will allow all customers — whether they’re running genuine Windows software or a pirated version — to upgrade to Windows 10 for free.
“We are upgrading all qualified PCs, genuine and non-genuine, to Windows 10″, he said in a telephone interview with Reuters. The plan is to “re-engage” with the hundreds of millions of users of Windows in China, he said, without elaboration.
Update: Microsoft states that even though they will be able to do the upgrade, this will not make them licensed or genuine. They will still be unsupported.