The WPA system checks ten categories of hardware:
1. Display Adapter
2. SCSI Adapter
3. IDE Adapter (effectively the motherboard)
4. Network Adapter (NIC) and its MAC Address
5. RAM Amount Range (i.e., 0-64mb, 64-128mb, etc.)
6. Processor Type
7. Processor Serial Number
8. Hard Drive Device
9. Hard Drive Volume Serial Number (VSN)
10. CD-ROM / CD-RW / DVD-ROM
It then calculates and records a number based on the first device of each type that was found during setup, and stores this number on your hard drive. Initially, this is sent to Microsoft in an automatic dial-up, together with the Product ID number derived from the 25-character unique Product Key used in setting up Windows.
If Service Pack 1 has been installed, the entire Product Key is also transmitted: This can then be checked against a list of known pirated keys
The hardware is checked each time Windows boots, to ensure that it is still on the same machine. Also, if you subsequently perform a complete format and reinstall of Windows, Microsoft’s activation center will have to be contacted again because the information held on the machine itself (the number previously written to your hard drive) will have been wiped out by reformatting the hard drive. If your hardware is substantially the same, this will be done by an automated call without your needing to talk to anyone.
What does ‘substantially the same’ mean? WPA asks for ‘votes’ from each of these ten categories: ‘Is the same device still around, or has there never been one?’ Seven Yes votes means all is well — and a NIC, present originally and not changed, counts for three yes votes! Minor cards, like sound cards, don’t come into the mix at all. If you keep the motherboard, with the same amount of RAM and processor, and an always present cheap NIC (available for $10 or less), you can change everything else as much as you like.
If you change the device in any category, you have lost that Yes vote — but will not lose it any more thereafter if you make changes in that category again. So, for example, you can install a new video display card every month for as long as you like.