Overview
Holding down the option key (⌥) at startup brings up the boot manager, allowing the user to choose which operating system to start up. When using a non-Apple keyboard, the alt key usually performs the same action. The boot manager can also be launched by holding down the “menu” button on the Apple Remote at startup.
Boot Camp displaced the open source Xom Project for dual booting Mac OS X and Windows XP.
Its functionality relies on BIOS emulation through EFI and a partition table information synchronization mechanism between GPT and MBR combined.
Read more about this topic: Boot Camp (software)