The simplest boot concept involves only one machine with one operating system. The boot process for this case has already been outlined. The same boot concept can be used for a Linux-only machine. Theoretically, you do not need to install a boot loader for such a system. However, in this case you would not be able to pass additional parameters to the kernel at boot time. For a machine with multiple operating systems, the following boot concepts are possible:
One operating system is booted from the hard disk. Other operating systems can be booted from the floppy disk drive.
Requirements: bootable floppy disk drive
Example: installation of Linux alongside Windows; booting of Linux from a boot disk
Advantage: no boot loader needs to be installed
Disadvantage: requires working boot disks and the boot process takes longer
Depending on the purpose of the computer, it is an advantage or disadvantage that Linux cannot be booted without a disk.
The system can also use a USB storage device to drive the boot process. This is very similar to the floppy method, except the necessary data is fetched from the USB memory stick.
This allows you to use several operating systems on a single machine and to choose among the installed systems at boot time. Switching to another operating system requires a reboot. However, the boot manager must be compatible with all the operating systems installed on the machine. The boot managers of SUSE LINUX (LILO and its successor GRUB) can boot all common operating systems. By default, SUSE LINUX installs the preferred boot manager in the MBR, unless this setting is changed during the installation.