Dual booting or dual-booting is the act of installing multiple operating systems on a computer, and choosing which one when it boots. This is accomplished by using a boot loader that can boot more than one operating system, such as NTLDR, LILO, or GRUB.

Dual booting is found in many situations, such as those where different software is available on different operating systems but cannot be run on a single system. A dual boot configuration will allow a user to use all of this different software on one computer. 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 a piece of virtual machine software to emulate another computer from within the operating system of choice.)

New Linux users migrating from the Microsoft Windows platform will usually dual boot, allowing them to try the new OS without losing the functionality and preferences of their existing setup. This is a major advantage, because it can save money on new hardware.

Unfortunately, compatibility issues arise with different operating systems sharing the same hard disk—one operating system may not be able to recognize the other's filesystem and thus may try to format it to its native file system, erasing existing data. This can be overcome by using multiple disks or by partitioning an existing disk to allow multiple filesystems.

When one has a similar configuration to those mentioned above, it is usually referred to as a dual boot configuration.

"Dual Boot" versus "Boot Manager"

From OS/2, the term dual boot has a more specific meaning.

In a dual boot installation, two (or more) operating systems are installed in a single partition. Selection of which operating system to boot is performed by running a dual boot utility program, which switches around the necessary boot loaders programs (by renaming files and copying boot sectors) to ensure that the chosen operating system is loaded at the next boot.

In a boot manager installation, by contrast, the two (or more) operating systems are installed in their own, separate, individual, partitions. Rather than booting directly into an operating system, the machine boots into a specialised, operating system neutral, boot loader program (such as IBM's eponymous Boot Manager) installed on a floppy disk or in its own partition on a hard disk. This boot loader program presents a list of the available bootable partitions from which the user can choose, and then loads and invokes the boot loader in the boot sector of the chosen partition, to boot the chosen operating system.

The Boot Manager program is capable of booting operating systems installed in partitions, and on disc devices, that the BIOS itself will not boot directly. Dual Boot relies upon the raw BIOS boot mechanism.

External links

• A tutorial on dual booting Windows XP and Linux (http://www.devhood.com/tutorials/tutorial_details.aspx?tutorial_id=405)
• WarpDoctor article on Boot Manager (http://www.warpdoctor.org./walter/articles/1998/aa091698.html)