The Windows and Linux Operating System are support the multi-boot system. For this purpose, an operating system should has flexible bootstrap loader mechanism.
Both windows and linux breeds have a bootstrap loader that will work with other versions of themselves, ie. Windows XP Win 2000 for example. However where is gets complicated is working on two operating systems that have different file system types and boot strap procedures. The reason you need GRUB or other boot-time programs is that they will properly start the boot process.
Some Linux Distributions use GRUB as a bootloader
