Partitioning your disk simply refers to the act of breaking up your disk into sections. Each section is then independent of the others. It's roughly equivalent to putting up walls inside a house; if you add furniture to one room it doesn't affect any other room.
If you already have an operating system on your system (Windows 9x, Windows NT/2000/XP, OS/2, MacOS, Solaris, FreeBSD, …) and want to stick Linux on the same disk, you will need to repartition the disk. Debian requires its own hard disk partitions. It cannot be installed on Windows or MacOS partitions. It may be able to share some partitions with other Linux systems, but that's not covered here. At the very least you will need a dedicated partition for the Debian root.
You can find information about your current partition setup by using a partitioning tool for your current operating system, such as fdisk or PartitionMagic. Partitioning tools always provide a way to show existing partitions without making changes.
In general, changing a partition with a file system already on it will destroy any information there. Thus you should always make backups before doing any repartitioning. Using the analogy of the house, you would probably want to move all the furniture out of the way before moving a wall or you risk destroying it.
If your computer has more than one hard disk, you may want to dedicate one of the hard disks completely to Debian. If so, you don't need to partition that disk before booting the installation system; the installer's included partitioning program can handle the job nicely.
If your machine has only one hard disk, and you would like to completely replace the current operating system with Debian GNU/Linux, you also can wait to partition as part of the installation process (Section 6.3.2.1, “Partitioning Your Disks”), after you have booted the installation system. However this only works if you plan to boot the installer system from tapes, CD-ROM or files on a connected machine. Consider: if you boot from files placed on the hard disk, and then partition that same hard disk within the installation system, thus erasing the boot files, you'd better hope the installation is successful the first time around. At the least in this case, you should have some alternate means of reviving your machine like the original system's installation tapes or CDs.
If your machine already has multiple partitions, and enough space can be provided by deleting and replacing one or more of them, then you too can wait and use the Debian installer's partitioning program. You should still read through the material below, because there may be special circumstances like the order of the existing partitions within the partition map, that force you to partition before installing anyway.
If your machine has a FAT or NTFS filesystem, as used by DOS and Windows, you can wait and use Debian installer's partitioning program to resize the filesystem.
If none of the above apply, you'll need to partition your hard disk before starting the installation to create partition-able space for Debian. If some of the partitions will be owned by other operating systems, you should create those partitions using native operating system partitioning programs. We recommend that you do not attempt to create partitions for Debian GNU/Linux using another operating system's tools. Instead, you should just create the native operating system's partitions you will want to retain.
If you are going to install more than one operating system on the same machine, you should install all other system(s) before proceeding with Linux installation. Windows and other OS installations may destroy your ability to start Linux, or encourage you to reformat non-native partitions.
You can recover from these actions or avoid them, but installing the native system first saves you trouble.
If you currently have one hard disk with one partition (a common setup for desktop computers), and you want to multi-boot the native operating system and Debian, you will need to:
Back up everything on the computer.
Boot from the native operating system installer media such as CD-ROM or tapes.
Use the native partitioning tools to create native system partition(s). Leave either a place holder partition or free space for Debian GNU/Linux.
Install the native operating system on its new partition.
Boot back into the native system to verify everything's OK, and to download the Debian installer boot files.
Boot the Debian installer to continue installing Debian.
If you are manipulating existing FAT or NTFS partitions, it is recommended that you either use the scheme below or native Windows or DOS tools. Otherwise, it is not really necessary to partition from DOS or Windows; the Linux partitioning tools will generally do a better job.
But if you have a large IDE disk, and are using neither LBA addressing, overlay drivers (sometimes provided by hard disk manufacturers), nor a new (post 1998) BIOS that supports large disk access extensions, then you must locate your Debian boot partition carefully. In this case, you will have to put the boot partition into the first 1024 cylinders of your hard drive (usually around 524 megabytes, without BIOS translation). This may require that you move an existing FAT or NTFS partition.
One of the most common installations is onto a system that already contains DOS (including Windows 3.1), Win32 (such as Windows 95, 98, Me, NT, 2000, XP), or OS/2, and it is desired to put Debian onto the same disk without destroying the previous system. Note that the installer supports resizing of FAT and NTFS filesystems as used by DOS and Windows. Simply start the installer, select the option to , select the partition to resize, and specify its new size. So in most cases you should not need to use the method described below.
Before going any further, you should have decided how you will be dividing up the disk. The method in this section will only split a partition into two pieces. One will contain the original OS and the other will be used for Debian. During the installation of Debian, you will be given the opportunity to use the Debian portion of the disk as you see fit, i.e., as swap or as a file system.
The idea is to move all the data on the partition to the beginning, before changing the partition information, so that nothing will be lost. It is important that you do as little as possible between the data movement and repartitioning to minimize the chance of a file being written near the end of the partition as this will decrease the amount of space you can take from the partition.
The first thing needed is a copy of fips which is
available in the tools/ directory on your nearest Debian
mirror. Unzip the archive and copy the files
RESTORRB.EXE, FIPS.EXE and
ERRORS.TXT to a bootable floppy. A bootable floppy can
be created using the command sys a: under DOS.
fips comes with very good documentation which you may
want to read. You will definitely need to read the documentation if
you use a disk compression driver or a disk manager. Create the disk
and read the documentation before you defragment the disk.
The next thing needed is to move all the data to the beginning of the partition. defrag, which comes standard with DOS 6.0 and later, can easily do the job. See the fips documentation for a list of other software that may do the trick. Note that if you have Windows 9x, you must run defrag from there, since DOS doesn't understand VFAT, which is used to support for long filenames, used in Windows 95 and higher.
After running the defragmenter (which can take a while on a large
disk), reboot with the fips disk you created in the
floppy drive. Simply type a:\fips and follow the directions.
Note that there are many other partition managers out there, in case fips doesn't do the trick for you.
If you are partitioning for DOS drives, or changing the size of DOS partitions, using Linux tools, many people experience problems working with the resulting FAT partitions. For instance, some have reported slow performance, consistent problems with scandisk, or other weird errors in DOS or Windows.
Apparently, whenever you create or resize a partition for DOS use, it's a good idea to fill the first few sectors with zeros. Do this prior to running DOS's format command, from Linux:
# dd if=/dev/zero of=/dev/hdXX bs=512 count=4