When a computer starts, certain BIOS routines are executed first in order to recognize and initialize hardware components such as the hard disk controllers, hard disks, network adapters, and so forth.
Afterwards, control of the boot process is taken over by the boot loader, which is located on a boot device such as a CD-ROM, hard disk, or network (PXE). The default boot loader for current SLES installations is GRUB. It starts a kernel and optionally an initial RAM disk (initrd).
Most operating systems accept parameters at the boot prompt to pass instructions to the kernel or initrd, which can influence such things as hardware initialization or function executions within the initrd.
In comparison to the boot process of a system already installed, other routines must be executed when you install a new system. Some of them are running in the background, and other routines might require manual administrative intervention. Most routines and modules that are necessary to install a new system on modern Linux distributions today are located within a special initrd, which is provided by the boot medium. This large initrd differs dramatically from the initrd used during a normal operating system boot.
Certain parameters specified at the boot prompt can influence how the system is installed. Some parameters ensure a proper network setup if necessary. Other parameters determine which installation repositories are used. An automated installation via AutoYaST must be initiated by a special boot parameter.