When you boot a PC, you cause it to execute a small program known as a boot loader. The purpose of the boot loader is to locate and read into memory the first stage of an operating system and transfer control to it. The operating system then locates and reads its remaining components as needed.
The simplest way to boot Linux is by using a floppy diskette. By doing so, you're able to leave the boot information on your hard drive untouched, ensuring that you can still boot Microsoft Windows or another operating system stored on the same hard drive. Moreover, some operating systems and virus protection programs prevent modification of the boot information on your hard drive. By booting from a floppy diskette, you avoid several potential problems.
However, many users find booting from a floppy disk slow or inconvenient. You don't have to boot Linux from a floppy diskette; you can boot it in any of several other ways. The most popular method is by using GRUB, which replaces the boot loader stored on your hard drive.
This appendix cannot describe the entire range of issues involved in booting Linux. Much of the information here is taken from several Linux HOWTOs that contain additional useful information on booting Linux: