retiredbrooklynboy :
I upgraded to windows 10 from 8.1. when windows 10 came out. I did create an ISO flashdrive of windows 10. Let's say, for example, that I needed to install a new hard drive, in the instructions mentioned, they say that I would need to put in the "product" key,
where would I get that?
I don't know what instructions you read, but no, you will NOT need the license key for this WIn 10.
When you Upgraded, you now have what is called a 'digital entitlement'. This is stored at the Microsoft activation server farm.
When you need to reinstall on a new hard drive, when it asks for the license key...there is a link at the bottom "Skip".
Click that and proceed. It will activate itself when the system goes online.
Also, you might want to create a new USB or DVD. The old one you have will have to run all the intervening updates.
A new one created today will have all of that in it already.
Create a new USB or DVD here:
https
/www.microsoft.com/en-us/software-download/windows10