A dual boot system is a computer that can boot into two different operating systems. While most computers automatically load a specific operating system (OS) at startup, a dual boot system allows you to choose what OS you would like to load. For example, a dual boot Windows system may provide an option to load either Windows 7 or Windows 8 at startup. Linux and Mac OS X users can install Windows to create a Linux/Windows or Mac/Windows dual boot configuration.
Dual boot systems are often used by computer enthusiasts, who prefer different operating systems for different tasks or want to run OS-specific applications. Software developers also use dual boot systems to test their software on multiple operating systems. A single dual boot system is more efficient than buying and setting up two separate computers.
In order to create a dual boot system, you first need to install a custom boot manager or "boot loader." This is a small program that loads near the beginning of the boot sequence before the OS loads. Common PC boot loaders include LILO and GRUB, which support Linux and Windows. Mac users can install Apple's Boot Camp utility. In most cases, you will need to install each operating system on a separate partitions. Linux installations may require multiple partitions just for the Linux OS. While the disk partitioning can be done manually, it is typically accomplished using a dual boot utility like EasyBCD (Windows) or Boot Camp (Mac OS X).
While many users still create dual boot machines, virtualization has become a more common way to run multiple operating systems on a single computer. Unlike dual booting, virtualization allows you to run multiple operating systems at the same time and switch between them without restarting. However, booting into a specific OS typically yields the best performance.
NOTE: Dual boot may also be called "multi boot," which refers to a computer than can load two or more different operating systems.