What is a hard disk partition?

A hard disk partition is a defined storage space on a hard drive.

Most operating systems allow users to divide a hard disk into multiple partitions, making one physical hard disk into several smaller logical hard disks.

Reasons to Use Hard Disk Partitions

A user may decide to split a hard disk into multiple partitions in order to organize his data more effectively. On Microsoft Windows machines, it is common to store the OS and applications on one hard disk partition and user data on another hard disk partition. When a problem occurs with Microsoft Windows, the OS partition can be completely formatted and reinstalled without affecting the data partition.

A user may decide to split a hard disk into multiple partitions because smaller partitions often have smaller cluster sizes. A cluster size is the smallest chunk of data which a partition can store. A large partition might have a cluster size of 16KB. This mens that a file with one character in it will occupy 16KB of space on the disk. In a smaller partition, that file might only require 4KB to store. This is a useful strategy if you are storing a large number of small files.

A user may have to split a large hard disk into multiple partitions if the hard disk is larger than the partition size supported by the operating system.

Creating Hard Disk Partitions

Most operating system use the 'fdisk' command to create hard disk partitions. Many operating systems also have graphical tools which accomplish the same task, such as EaseUS Partition Master.

Hard Disk Partitions and File Systems

You don't actually store data in hard disk partitions.

You store file systems in hard disk partitions and then you store data in these file systems.

Some operating systems blur the lines between partitions and file systems.

The Partition Table

Partition information is stored in the partition table, a reserved area at the beginning of a hard disk.

Extended Partitions

A standard partition table is only able to store information about four partitions. At one time this meant that a hard disk could have a maximum of four partitions.

To work around this limitation, extended partitions were created.

An extended partition stores information about other partitions. By using an extended partition, you can create many more than four partitions on your hard disk.

The four standard partitions are often called the primary partitions.

Partitions configured into an extended partition are often referred to as logical partitions.

Partition Types

When a partition is created, a special byte of data is written to record what type of partition it is.

Because one hard disk may be shared by multiple operating systems, operating systems tend to agree on the meaning of these values.

The table below lists some of the partition types in use.

Partition Number Partition Type
00 Empty
01 DOS 12-bit FAT
02 XENIX root
03 XENIX usr
04 DOS 16-bit FAT <=32M
05 DOS Extended Partition
06 DOS 16-bit FAT >=32
07 OS/2 HPFS, WinNT NTFS
08 AIX
09 AIX bootable
0a OS/2 Boot Manager
0b Win95 FAT32
0c Win95 FAT32 (LBA)
0e Win95 FAT16 (LBA)
0f Win95 Extended (LBA)
35 OS/2 JFS
39 Plan 9
40 Venix 80286
51 Novell
52 Microport
63 Unix System V, Mach, GNU HURD
64 Novell Netware 286
65 Novell Netware 386
75 PIC/IX
80 MINIX until 1.4a
81 MINUX, Linux
82 Solaris X86, Linux swap
83 Linux native
85 Linux extended
93 Amoeba
94 Amoeba BBT
a5 FreeBSD, NetBSD, BSD/386, 386BSD
a6 OpenBSD
a7 NEXTSTEP
b7 BSDI BSD/386 filesystem
b8 BSDI BSD/386 swap
be Solaris 8 bootable
bf Solaris x86
c7 Syrinx
db CP/M
e1 DOS access
e3 DOS R/O
eb BeOS BFS
fb VMWare filesystem
fc VMWare swap
f2 DOS secondary
ff Xenix Bad Block Table

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