There are still situations where you'll run into product keys with Windows 10. If you buy a physical retail edition such as on a USB stick or DVD, you'll still get a product key. Microsoft told us that "your activation product key stays with your PC." We're not clear if that means product keys work as digital entitlements, or whether you'll be managing product keys the old fashioned way--by stashing that product key somewhere safe for later use. We're double-checking this with Microsoft and will update this article should the company respond.
One sticking point with digital entitlements is that because it's dependent on your hardware configuration, making a significant change can wipe out the entitlement. If you swap out your motherboard, for example, your digital entitlement will likely disappear and Windows 10 won't activate. If that happens, you'll have to make a call to Microsoft's customer support line to re-activate your copy of Windows.
Keep in mind we're talking significant hardware changes here. If you swap out your hard drive for an SSD or add more RAM, you shouldn't see any problems.
I don't know about you, but if I ever have to look at a product key again it'll be too soon.
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