These components are: the volume serial number of the boot disk (created by formatting); the MAC address
(a unique number embedded in the hardware) of an installed network adapter; the PCI hardware identification data from an installed CD-ROM drive, video card, IDE adapter, SCSI adapter and hard drive; the CPU model and serial numbers; the amount of RAM, and whether the system is dockable (laptop) or not (desktop).
Windows XP reevaluates this combination of hardware items whenever it starts up and discovers new devices. Microsoft now says that you can change up to six devices at a time, or your network interface card
and three other devices, without having to reactivate. If you change the same component, such as your video card, over and over, it counts as only one change, and new components, such as a new modem or an extra memory module, do not count as a change. Meanwhile, if you buy a new PC with XP preinstalled, Microsoft says the computer manufacturer will probably link activation solely to the system BIOS
. That means that you can change every single hardware component on your machine, and, as long as the BIOS is unchanged, you won't have to reactivate XP.