- When a computer starts, it first runs the BIOS software. This essential program identifies the connected hardware and decides how to proceed with startup. Most computers contain a hard drive storing an operating system, such as Windows or OS X, and the BIOS recognizes the hard drive as a bootable device and runs the operating system. Boot discs bypass this process by presenting an alternate bootable device that the BIOS will start from instead of the hard drive. This allows boot discs to work even if the system has no working operating system.
- A disc with compatible software is not bootable unless it contains a boot sector, a small bit of code that allows it to run at startup. Other than this requirement, a boot disc may contain any imaginable software. Windows and OS X operating system discs are boot discs capable of installing the OS and also running repair programs. Linux distributions also use boot discs. Some backup programs, such as Norton Ghost, use boot discs for recovery images. Some disk partitioning and management tools store on boot discs for access on malfunctioning machines.
- Users often need to create boot discs from downloaded software or stored backup files. Several programs can add boot sectors to burned discs, including Nero, MagicISO and PE Builder. Only software created specifically to work with boot discs will work properly when burned to CD or DVD.
- The BIOS software stores a list of bootable hardware devices arranged in order of startup preference. During startup, the BIOS goes through the list and starts the first bootable device it finds. If the system's hard drive is listed before a boot disc, the system will start normally even with a boot disc in the drive. Change the boot order by opening the BIOS menu at startup, usually by pressing the corresponding function key. The process differs between manufacturer's, but look for a key labeled "BIOS" or "Setup."
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