I could not resist posting on this, even though
@shmu26 got it right. I was running a fairly new MSI-based desktop and decided to build a more powerful Asus-based machine for gaming. They were both Intel Z170 chipset boards, so I moved DDR4 memory sticks, PSU, my GTX 970 graphics card, and the SSD that was my Win10 boot drive over. When I finished the build, I booted it, fully expecting the machine to choke and take me to BIOS, which it did, but only to confirm the new processor. That done, I rebooted and it went right by BIOS and booted into Windows, taking only about an extra minute on top of the usual 20-second boot. I was flabbergasted! Win10 had seen the new hardware, replaced all the old hardware drivers with generic drivers and, since I was hardwired to my modem/router, immediately started downloading the correct drivers, and in the end I only had to add a couple downloaded Asus drivers for minor hardware that either wasn't working, or wasn't working as well as it should. I checked right away and was shocked to find that Windows was activated.
However, (you knew there had to be a however, right?) after about three days I got a popup notice that I needed to activate Windows, and when I entered my Pro product key, it was rejected. Even before I could call in, Office 2013 popped up a notice that I was running it on too many computers.
Twenty minutes with only the initial support tech had me fully sorted and activated on both pieces.
I must say I was mighty impressed. I've been a user, tech and builder using MS since Windows 2, with forays into Linux and even Mac. I must say, this is a very, very good OS.