Kilkis wrote:Once you upgrade to Win 10 you have to get a new product key. The old Win 7/8 one will not work. There is an App that will do this. I will try and post the details in the next couple of days.
While this was the perceived wisdom in the technical press when I made this post, it now turns out that this statement is not true. There is a new product key which can be discovered with an App but it is meaningless because it is a generic code used for all upgrades and only works as part of an upgrade process. You cannot use it to do a clean install. When you upgrade to Windows 10 the system activates using this generic key and also sends a fingerprint of your PC to Microsoft, e.g. details on the processor, memory, disk drives, graphics cards and any other installed hardware. If you subsequently decide to do a clean install, using a downloaded ISO file of the Windows system, it activates checking that fingerprint so you don't need a product key. I guess minor changes would be allowed, e.g. doing a clean install on a new SSD that wasn't in the original PC as long as everything else stays the same. You might have to confirm directly with Microsoft what you were doing and why.
It is possible to do a clean install on a new PC BUT only up to 29 July next year. You would need to install the original Windows 7/8/8.1 on the new PC using the original product key provided when you bought it. You might have to go through some process with Microsoft to verify that you have removed it from the old PC. You then upgrade to Windows 10 on the new PC. If you do the upgrade before 29 July 2016 I think you should be able to do a clean install after that. Obviously it means that if you decide to build a new PC after 29 July 2016 and want it to run on Windows 10 you will have to buy it. Note that you need to be careful how you prepare the installation media, e.g. CD/USB stick, using the WIndows 10 Media Creation Tool
OEM versions of Windows 7/8/8.1 can be upgraded on their original machine I believe but cannot be transferred to a new machine. That is nothing to do with Windows 10 but simply a restriction of the OEM software.
When it upgrades it keeps the original installation files. You can thus revert to your original version if you don't like Windows 10. Be warned it only keeps the files for 1 month so after that you would need to do a complete reinstall from your original media.
Computer shopper gives Windows 10 a good review, see Windows 10 Review