Analysts from Gartner believe that Apple might use the Trusted Platform Module (TPM) chip to ensure that only Mac systems will be able to run its Mac OS X operating system.
The TPM chip from Trusted Computing Group can be used to securely store and encrypt information, and each chip has a unique identifier code. It cold be used to distinguish a Mac system from a model made by Dell, HP or any other vendor.
Computers from Dell, IBM and IBM/Lenovo already use the TPM chip. IBM for instance uses the chip to allow users to store passwords and encrypt contents of the HDD. Microsoft will also use TPM for Windows Longhorn:
The upcoming Longhorn version of Windows relies on the TPM for a technology dubbed Secure Startup, which blocks access to the computer if the content of the hard drive is compromised. This prevents a laptop thief swapping out the hard drive, or booting the system from a floppy disk to circumvent security features.