Datasheet

“main” (Installation and Administration) — 2004/6/25 — 13:29 — page 206 — #232
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Booting Other Operating Systems from a Floppy Disk
One operating system is booted from the hard disk. Other operating
systems can be booted from the floppy disk drive.
For example, use it for an installation of Linux alongside Windows —
boot Linux from a boot disk. This method requires a bootable floppy
disk drive. The advantage is that no boot loader needs to be installed.
However, it 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.
Booting Another Operating System from a USB Storage Device
The system can also use a USB storage device to drive the boot pro-
cess. This is very similar to the floppy method, except the necessary
data is fetched from the USB memory stick.
Installing a Boot Manager This allows you to use several operating sys-
tems 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 oper-
ating systems installed on the machine. The boot managers of SUSE
LINUX (LILO and its successor GRUB) can boot all common operat-
ing systems. By default, SUSE LINUX installs the preferred boot man-
ager in the MBR, unless this setting is changed during the installation.
8.3 Map Files, GRUB, and LILO
The main obstacle for booting an operating system is that the kernel is usu-
ally a file within a file system on a partition on a disk. These concepts are
unknown to the BIOS. To circumvent this, maps and map files were intro-
duced. These maps simply note the physical block numbers on the disk
that comprise the logical files. When such a map is processed, the BIOS
loads all the physical blocks in sequence as noted in the map, building the
logical file in memory.
In contrast to LILO, which relies entirely on maps, GRUB tries to gain in-
dependence from the fixed maps at an early stage. GRUB achieves this by
means of the file system code, which enables access to files by way of the
path specification instead of the block numbers.
206 8.3. Map Files, GRUB, and LILO