"Specifically, product activation determines tolerance through a voting mechanism," the XP Activation FAQ says. "There are 10 hardware characteristics used in creating the hardware hash. Each characteristic is worth one vote, except the network card which is worth three votes. When thinking of tolerance, it's easiest to think about what has not changed instead of what has changed. When the current hardware hash is compared to the original hardware hash, there must be 7 or more matching points for the two hardware hashes to be considered in tolerance."
"It's important that people understand the OEM EULA when it says that your OEM Vista (XP is the same) can not be transferred to a new computer, and a new (upgraded) motherboard is also considered a new computer," the system builder added. "I've activated hundreds of PCs over the years and have never had an activation rep ask if I am transferring the OEM software to a new PC. The only question that you must answer correctly (no) in order to receive the activation code is: "Is this version of Windows on more than one PC?". Therefore the end user assumes that since they received an activation code they must be legal."