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<sect2 arch="x86"><title>Partitioning for &arch-title;</title>
<para>
The PC BIOS generally adds additional constraints for disk
partitioning. There is a limit to how many <quote>primary</quote> and
<quote>logical</quote> partitions a drive can contain. Additionally, with pre
1994-98 BIOS, there are limits to where on the drive the BIOS can boot
from. More information can be found in the
<ulink url="&url-partition-howto;">Linux Partition HOWTO</ulink> and the
<ulink url="&url-phoenix-bios-faq-large-disk;">Phoenix BIOS FAQ</ulink>, but
this section will include a brief overview to help you plan most
situations.
</para><para>
<quote>Primary</quote> partitions are the original partitioning scheme for PC
disks. However, there can only be four of them. To get past this
limitation, <quote>extended</quote> and <quote>logical</quote> partitions were invented. By
setting one of your primary partitions as an extended partition, you
can subdivide all the space allocated to that partition into logical
partitions. You can create up to 60 logical partitions per extended
partition; however, you can only have one extended partition per
drive.
</para><para>
Linux limits the partitions per drive to 15 partitions for SCSI disks
(3 usable primary partitions, 12 logical partitions), and 63
partitions on an IDE drive (3 usable primary partitions, 60 logical
partitions). However the normal &debian; system provides
only 20 devices for partitions, so you may not install on partitions
higher than 20 unless you first manually create devices for those
partitions.
</para><para>
If you have a large IDE disk, and are using neither LBA addressing,
nor overlay drivers (sometimes provided by hard disk manufacturers),
then the boot partition (the partition containing your kernel image)
must be placed within the first 1024 cylinders of your hard drive
(usually around 524 megabytes, without BIOS translation).
</para><para>
This restriction doesn't apply if you have a BIOS newer than around
1995-98 (depending on the manufacturer) that supports the <quote>Enhanced
Disk Drive Support Specification</quote>. Both Lilo, the Linux loader, and
Debian's alternative <command>mbr</command> must use the BIOS to read the
kernel from the disk into RAM. If the BIOS int 0x13 large disk access
extensions are found to be present, they will be utilized. Otherwise,
the legacy disk access interface is used as a fall-back, and it cannot
be used to address any location on the disk higher than the 1023rd
cylinder. Once Linux is booted, no matter what BIOS your computer
has, these restrictions no longer apply, since Linux does not use the
BIOS for disk access.
</para><para>
If you have a large disk, you might have to use cylinder translation
techniques, which you can set from your BIOS setup program, such as
LBA (Logical Block Addressing) or CHS translation mode (<quote>Large</quote>).
More information about issues with large disks can be found in the
<ulink url="&url-large-disk-howto;">Large Disk HOWTO</ulink>. If you
are using a cylinder translation scheme, and the BIOS does not support
the large disk access extensions, then your boot partition has to fit
within the <emphasis>translated</emphasis> representation of the
1024th cylinder.
</para><para>
The recommended way of accomplishing this is to create a small (5-10MB
should suffice) partition at the beginning of the disk to be used as
the boot partition, and then create whatever other partitions you wish
to have, in the remaining area. This boot partition
<emphasis>must</emphasis> be mounted on <filename>/boot</filename>,
since that is the directory where the Linux kernel(s) will be stored.
This configuration will work on any system, regardless of whether LBA
or large disk CHS translation is used, and regardless of whether your
BIOS supports the large disk access extensions.
</para>
</sect2>
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