Fdisk

fdisk (for "fixed disk") is a commonly used name for a command-line utility that provides disk partitioning functions in an operating system. However, each version of fdisk is independent of the others, and aside from their name and similar purpose, they are unrelated.

fdisk in DOS and Windows

Most DOS FDISK programs, including the FDISK program that came with the original Windows 95, are only capable of creating FAT partitions of types FAT12 and FAT16.

A derivative of the MS-DOS FDISK was provided with Windows 95, Windows 98, and later Windows Me. Only those FDISK versions shipping with Windows 95B or later are able to manipulate FAT32 partitions. Windows 2000 and later do not use FDISK, they have the Logical Disk Manager feature.

Unlike the fdisk programs for other operating systems, the FDISK programs for DOS and Windows 9x/Me not only alter data in the Partition Table, but will also overwrite many sectors of data in the partition itself. Users must be sure the correct disk/partition has been chosen before using a DOS/Windows FDISK for partitioning.

The implementation of fdisk in FreeDOS has many advanced features and is free software.

fdisk in Unix-like systems

Linux needs at least one partition, namely for its root file system. It can use swap files and/or swap partitions. Usually one will want a second Linux partition dedicated as a swap partition. See also: cfdisk.

Other Intel based Unixes typically use a more elaborate arrangement. BSD-derived systems use a disklabel as their primary method of identifying distinct sections of the disk, usually termed "slices". These slices may or may not correspond to partitions enumerated in the master boot record. A typical arrangement is for the entire Unix system to have a single partition allocated to it which is then subdivided into distinct slices for each filesystem and the swap area. Other partitions outside this dedicated one may be legitimately referenced in a disklabel - this is particularly true in dual boot scenarios, where it is desired that the Unix system be able to access partitions used by other operating systems residing on the same machine.

It should be noted that this approach is not mandatory since the MBR and bootlabel are two distinct records - it is technically possible (but not recommended) for the disklabel to describe a filesystem on an area of the disk that the MBR regards as unused. Regardless of the correlation between the two records, the 'entire disk' slice of the disklabel usually corresponds to the entire physical disk and not solely to the dedicated partition. In order to eliminate any possibility of confusion caused by these two (possibly contradictory) records, the sysadmin of these systems may elect to eliminate the master boot record from the disk. However, a disk laid out this way is unusable by any other operating systems.

The situation with System V-derived systems is similar to that with the BSDs, although the terminology usually used differs slightly. In this instance a single partition is subdivided using the "divvy" command, and such areas are often simply referred to as "divisions".

On older Intel compatible hardware, the BIOS that boots the system can often only access the first 1024 cylinders of the disk. For this reason people with large disks often create a third partition, just a few MB large, typically mounted on /boot or /stand, to store the kernel image and a few auxiliary files needed at boot time, so as to make sure that they are accessible to the BIOS. There may also be reasons of security, ease of administration and backup, or testing, to use more than the minimum number of partitions.

fdisk in OS/2

OS/2 shipped with two partition table managers up until version 4.0. These were the text mode "fdisk" and the GUI-based "fdiskpm". The two have identical functionality, and can manipulate both FAT partitions and the more advanced HPFS partitions.

OS/2 versions 4.5 and higher (including eComStation) can use the JFS filesystem as well as FAT and HPFS, and replace fdisk with the Logical Volume Manager (LVM).

ee also

* List of disk partitioning software

External links

* [http://uw713doc.sco.com/en/man/html.1M/fdisk.1M.html UnixWare 7, fdisk(1M)]
* [http://tldp.org/HOWTO/Partition/fdisk_partitioning.html Linux Partition HOWTO. Partitioning with fdisk]
* [http://www.die.net/doc/linux/man/man8/fdisk.8.html Linux Programmer's Manual, fdisk(8)]
* [http://www.freebsd.org/cgi/man.cgi?fdisk FreeBSD System Manager's Manual, FDISK(8)]