Apple filed a patent application describing a method for securely running Mac OS X on specific hardware. This means Mac OS X will only run on specific Intel x86 hardware, preventing non-Macintosh users to install a copy of Mac OS X on their system.
In its application, Apple describes a means of securing code using either a specific hardware address or read-only memory (ROM) serial number. Apple also talks about securing the code while interchanging information among multiple operating systems. Mac OS X, Windows and Linux are called out specifically in the filing.