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Artist's depiction of a boot manager's menu offering a choice between Microsoft Windows and Linux operating systems.

Dual booting or dual-booting is the act of installing multiple operating systems on a computer, and being able to choose which one to boot when switching on the computer power. The program which makes dual booting possible is called a boot loader.

Dual booting is useful in many situations, such as those where several pieces of software require different operating systems and cannot be run on a single system. A dual boot configuration will allow a user to use all of this software on one computer.

Another reason for setting up a dual boot system can be that one wants to investigate or test a new operating system without switching completely. Dual booting allows one to get to know the new system, configure all applications needed and migrate data before making the final step and removing the old operating system. For example, new users of Linux distributions migrating from the Microsoft Windows platform will usually dual boot, allowing them to try the new operating system without losing the functionality and preferences of their existing setup. This is often accomplished by using a boot loader that can boot more than one operating system, such as NTLDR, LILO, or GRUB.

Dual booting can also aid software developers where multiple operating systems are required for development or testing purposes. Having these systems on one machine can greatly reduce hardware costs. (However hardware costs are counterbalanced by system management costs, and the costs of the unavailability of the software that cannot be run at any given moment. Another solution to these problems is to use virtual machine software to emulate another computer from within the operating system of choice.)

Compatibility issues may arise with different operating systems: one operating system may not be able to recognize the other operating system's file system and thus may try to format it to its native file system, erasing existing data. This happens more often when the file systems are in separate partitions on one disk than when they are on separate disks.^{[citation needed]} Sometimes an administrator must manually configure one operating system to ignore the other disk or partition in order to allow multiple file systems.

Main article: Boot Camp

Boot Camp allows owners of Intel-based Apple Macintosh computers to install Windows XP and Vista on their Macs. The software comes bundled with Mac OS X 10.5 Leopard, Apple's latest version of the Operating System included on their computers. Previously the application was available in beta version as a download from Apple's website.

Boot Camp allows non-destructive disk partitioning and resizing of HFS+ filesystems, boot menu options, and an option to burn a CD with necessary device drivers. Since Windows XP is incompatible with Extensible Firmware Interface (the successor to legacy BIOS), the firmware on early Intel Macs need to be updated to support BIOS emulation first. BIOS emulation is achieved with a compatibility support module (CSM). Apple does not support non-Windows partition formats or drivers so therefore configuring other operating systems is not be directly possible through Boot Camp itself. However, any operating system which can utilize the BIOS emulation of Intel Macintosh can be made to work, including non-XP versions of Windows. The Ubuntu Linux distribution is particularly popular for this purpose because they provide an option to use proprietary device drivers along with open source drivers.

On a computer with both Windows Vista and either Windows XP or Windows Server 2003 installed, Windows XP or Windows Server 2003 deletes any existing System Restore points belonging to Windows Vista during boot. Microsoft confirms this issue but maintains that it is a fundamental function of the way XP works and cannot be changed. The solution, Microsoft maintains, is to install Windows Vista on a separate physical drive, not a partition, and make it invisible to XP.^{[citation needed]}

• GNU GRUB
• Multiboot Specification

• A tutorial on dual booting Windows XP and Linux
• A tutorial on dual booting Windows XP and Windows Vista
• WarpDoctor article on Boot Manager
• Wiki tutorial for using Windows XP on a Mac
• Installing Windows XP:Dual-Booting Versus Single Booting
• A tutorial on dualbooting/multibooting with Windows NTLDR and Linux LILO/GRUB
• Instructions on how to make your Playstation 3 dual boot applicable