What is a partition?

When PC hard disks were invented people soon wanted to install multiple operating systems, even if their system had only one disk. So a mechanism was needed to divide a single physical disk into multiple logical disks. So that's what a partition is: A contiguous section of blocks on your hard disk that is treated like a completely seperate disk by most operating systems.

It is fairly clear that partitions must not overlap: An operating system will certainly not be pleased, if another operating system installed on the same machine were overwriting important information because of overlapping partitions. There should be no gap between adjacent partitions, too. While this constellation is not harmful, you are wasting precious disk space by leaving space between partitions.

A disk need not be partitioned completely. You may decide to leave some space at the end of your disk that is not assigned to any of your installed operating systems, yet. Later, when it is clear which installation is used by you most of the time, you can partition this left over space and put a file system on it.

Partitions can not be moved nor can they be resized without destroying the file system contained in it. So repartitioning usually involves backup and restore of all file systems touched during the repartitioning. In fact it is fairly common to mess up things completely during repartitioning, so you should back up anything on any disk on that particular machine before even touching things like fdisk.

Well, some partitions with certain file system types on them actually can be split into two without losing any data (if you are lucky). For example there is a program called "fips" for splitting MS-DOS partitions into two to make room for a Linux installation without having to reinstall MS-DOS. You are still not going to touch these things without carefully backing up everything on that machine, aren't you?

Related HOWTOs

To learn how to estimate the various size and speed requirements for different parts of the filesystem, see "Linux Multiple Disks Layout mini-HOWTO", by Gjoen Stein.

For instructions and considerations regarding disks with more than 1024 cylinders, see "Linux Large Disk mini-HOWTO", AndriesBrouwer.

For instructions on limiting disk space usage per user (quotas), see "Linux Quota mini-HOWTO", by Albert M.C. Tam <bertie@scn.org>

Currently, there is no general document on disk backup, but there are several documents with pointers to specific backup solutions. See "Linux ADSM Backup mini-HOWTO", by Thomas Koenig <Thomas.Koenig@ciw.uni-karlsruhe.de> for instructions on integrating Linux into an IBM ADSM backup environment. See "Linux Backup with MSDOS mini-HOWTO", by Christopher Neufeld <neufeld@physics.utoronto.ca> for information about MS-DOS driven Linux backups.

For instructions on writing and submitting a HOWTO document, see the Linux HOWTO Index, by Tim Bynum <linux-howto@sunsite.unc.edu>.

Browsing through /usr/src/linux/Documentation can be very instructive, too. See ide.txt and scsi.txt for some background information on the properties of your disk drivers and have a look at the filesystems/ subdirectory.