HDD's with Windows 10 OS are interchangeable This post is just about some experiences I'd over the past few weeks with Windows 10 Activations. If someone has a similar problem this post maybe helps to solve. From some experiences, I'd over the last few weeks, I found out that an HDD with installed and activated Windows 10 Retail (Home/Pro) with Digital License could be used on any computer which also had a previous Windows 10 (Home/Pro) on a different HDD and gets activated with no any question asked. It doesn't matter if the Hardware is totally different! For a fully restructuring of a LAN/wired Network and upgrade of 30 computers to more powerful and newer hardware, I started to test those old machines (because of confidential and other files) with my Test-HDD's and found directly that only update to hardware related drivers was needed, but activation because the existing Digital Licenses of those old machines was taken for an auto-activation with my own Windows 10 Digital License. All those old machines were mainly from different Hardware, and quite outdated already. The new machines are all the exact same Hardware and all would get Windows 10 Pro too. Now the question came up about the activations for those new machines. So, I'd took the first machines, installed Windows 10 Pro and activated with a Windows 8.1 Pro Key which worked well. Done all available updates for the OS and Drivers with no problems. After done that, I cloned that HDD with HDClone 6 and placed that HDD in the next new machine and booted from it: activated with a Digital License, and so for the next 3 machines! The next new machine didn't activate and I needed to call to MS Activation Center and got a new Activation Code. For the remaining 24 new machines, I just used to install Windows 10 Pro and used the Windows 8.1 Product key for activation for the next 5 machines, which worked for all now. By all that I found out, that up to 5 Computers a day, no problem, just if I exceed that 5 I need to call the activation center again. Windows and other Microsoft Activation from within Thailand will be going to either Singapore or Mumbai/India and could be done using a Tollfree Phone Number without any cost. Thanks for reading. Please do not post any harassing, abusing and otherwise bad answer and/or questions.