Booting the System

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C. Booting the System This appendix describes what happens during the GNU/Linux boot process. How you boot your system depends on how you set things up when you installed Debian. Most likely, you just turn the computer on. But you may have to insert a floppy disk first. Linux is loaded by a program called LILO, or LInux LOader. LILO can also load other operating systems and ask you which system you’d like to load. The first thing that happens when you turn on an Intel PC is that the BIOS executes. BIOS stands for Basic Input Output System. It’s a program permanently stored in the computer on read-only chips. It performs some minimal tests and then looks for a floppy disk in the first disk drive. If it finds one, it looks for a “boot sector” on that disk and starts executing code from it, if there is any. If there is a disk but no boot sector, the BIOS will print a message like this: Non-system disk or disk error. Removing the disk and pressing a key will cause the boot process to resume. If there isn’t a floppy disk in the drive, the BIOS looks for a master boot record (MBR) on the hard disk. It will start executing the code found there, which loads the operating system. On GNU/Linux systems, LILO can occupy the MBR and will load GNU/Linux.