A product key is a 25-character code that's used to activate Windows. Activation helps verify that Windows hasn't been used on more PCs than the Microsoft Software License Terms allow.
Your product key is on a card inside the box that the Windows DVD came in—or in an email that shows that you bought Windows.
It looks like this:
PRODUCT KEY: XXXXX-XXXXX-XXXXX-XXXXX-XXXXX. If you bought a PC with Windows preinstalled, contact the PC manufacturer for the original key.
It's a good idea to save a copy of your product key for your records in case you ever need to reinstall Windows.
See all support pages for install, upgrade, & activate.
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