|Previous versions of windows used a formula to determine if the key you enter is valid. They would make batches using the same formula so that any key valid on one of those disks would work for all of them.|
I'm sure it's the same way with XP because it would be too expensive to write into each disk a unique product key. I have no idea how many batches they made that had the same formula. With 98 they used a different formula for upgrade disks, retail full install disks and full install OEM disks. Most of the 98 computers I came across had OEM installations and their keys always worked with the OEM disks I had when I refurbished those computers with a fresh install.
If you have an XP disk and maybe a COA sticker with a product key from a system you want to do a reinstall on, you'll just have to try it and see if setup takes it.
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