Booting - Boot Devices (IBM PC)

Boot Devices (IBM PC)

The boot device is the device from which the operating system is loaded. A modern PC BIOS supports booting from various devices, typically a local hard disk drive via the Master Boot Record (MBR) (and of several MS-DOS partitions on such a disk, or GPT through GRUB 2), an optical disc drive (using El Torito), a USB mass storage device (FTL-based flash drive, SD card, or multi-media card slot; hard disk drive, optical disc drive, etc.), or a network interface card (using PXE). Older, less common BIOS-bootable devices include floppy disk drives, SCSI devices, Zip drives, and LS-120 drives.

Typically, the BIOS will allow the user to configure a boot order. If the boot order is set to "first, the DVD drive; second, the hard disk drive", then the BIOS will try to boot from the DVD drive, and if this fails (e.g. because there is no DVD in the drive), it will try to boot from the local hard drive.

For example, on a PC with Windows XP installed on the hard drive, the user could set the boot order to the one given above, and then insert a Linux Live CD in order to try out Linux without having to install an operating system onto the hard drive. This is an example of dual booting ‒ the user choosing which operating system to start after the computer has performed its POST. In this example of dual booting, the user chooses by inserting or removing the CD from the computer, but it is more common to choose which operating system to boot by selecting from a menu using the computer keyboard. (Typically F11 or ESC)