Datasheet

“main” (Installation and Administration) — 2004/6/25 — 13:29 — page 205 — #231
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8
Booting and Boot Managers
8.1.2 Boot Sectors
Boot sectors are the first sectors on a hard disk partition, except in the case
of extended partitions, which are just containers for other partitions. Boot
sectors offer 512 bytes of space and are designed to contain code capable of
launching an operating system on this partition. Boot sectors of formatted
DOS, Windows, and OS/2 partitions do exactly that (in addition, they con-
tain some basic data about the file system structure). In contrast, the boot
sector of a Linux partition is empty (even after creating a file system on it).
Thus, a Linux partition cannot bootstrap itself, even if it contains a kernel
and a valid root file system. A boot sector with a valid start code contains
the same magic number as the MBR in its last two bytes (AA55).
8.1.3 Booting DOS or Windows
The DOS MBR of the first hard disk contains information that determines
which partition of a hard disk is active (bootable). The active partition is
searched for the operating system to boot. Therefore, DOS must be installed
on the first hard disk. The DOS program code in the MBR is the first stage
of the boot loader. It checks if the specified partition contains a valid boot
sector.
If this is the case, the code in this boot sector can be loaded as the second
stage of the boot loader, which in turn loads the system programs. Subse-
quently, the DOS prompt appears or the Windows user interface is started.
In DOS, only one primary partition can be marked as active. This is why
you cannot install the DOS system on logical drives in an extended parti-
tion.
8.2 Boot Concepts
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:
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SUSE LINUX Enterprise Server