Not sure how much of this applies to Windows 7, but I've learned some interesting things about Windows XP activation over the years. This will likely provoke some cries of "but that violates the license agreement, blah blah blah"... yeah, okay, maybe. What interests me is whether Microsoft actually allows the action or not.
From what I can deduce, activation works like this: First, Windows generates a hash (or maybe multiple hashes) based on your current hardware configuration and the license key you entered. Certain components like the motherboard and NIC are given more weight here. Next, you transmit your hash(s) to Microsoft. If everything is gucci, they record the activation, run your hash(s) through a function that generates another hash, and transmit this new hash back to you. Windows then compares this number against one it calculated internally. If they match, activation is successful and Windows never needs to call home again. If the hardware configuration changes enough, though, the numbers will no longer match and Bad Things will happen. Maybe you can reactivate, maybe not; I've never gone down this road.
The key thing about Windows XP activation is that Microsoft's servers only store activation information for 120 days. Confirmed this experimentally for OEM keys; not sure if it applies to retail keys. In any case, this is super useful for the following reasons: First, as long as you don't need to activate too often, a single OEM key is all you'll ever need. Second, knowing this exponentially expands your options for obtaining a working key. Just need to find a key that hasn't been used in the past 120 days and no one is likely to use again. Scrapped computers with COAs on the side are perfect for this. There are some restrictions: for example, Windows XP Pro keys can only be used with Pro installation media, and the same goes for Home. I think there are also some shenanigans with service pack versions, like newer keys won't work with older media. This part almost certainly applies to Windows 7 and its different versions as well.
Another useful thing has to do with activation method. I only discovered this in the past year or so since online activation stopped working for Windows XP. As of today, the only legit way I know of to activate Windows XP is to call Microsoft's activation center at 888-352-7140. There's no human interaction involved, just a surprisingly slick robot. The downside of phone activation is you have to painstakingly speak or type your hash(s) into the system, then it reads the second hash back to you and you have to painstakingly enter it into the prompt. The upside is you can save the second hash and use it again. As long as the hardware configuration doesn't change too much, it should work for the life of the system. No need to interact with Microsoft on subsequent installs. Pretty nifty.
Hope some of this will be helpful in getting Windows 7 activated. I'm sure there are some less legit ways to do it but I've never trusted those 😆
