When a computer with Red Hat Enterprise Linux is turned on, the operating system is loaded into memory by a special program called a boot loader. A boot loader usually exists on the system's primary hard drive (or other media device) and has the sole responsibility of loading the Linux kernel with its required files or (in some cases) other operating systems into memory.
2.1. Boot Loaders and System Architecture
Each architecture capable of running Red Hat Enterprise Linux uses a different boot loader. The following table lists the boot loaders available for each architecture:
Table 2.1. Boot Loaders by Architecture
| Architecture || Boot Loaders |
| AMD® AMD64 || GRUB |
| IBM® eServer™ iSeries™ || OS/400® |
| IBM® eServer™ pSeries™ || YABOOT |
| IBM® S/390® || z/IPL |
| IBM® eServer™ zSeries® || z/IPL |
| Intel® Itanium™ || ELILO |
| x86 || GRUB |
This chapter discusses commands and configuration options for the GRUB boot loader included with Red Hat Enterprise Linux for the x86 architecture.