Definition: Hard disk partition is a defined storage space on a hard drive.
Depending of the user needs, it is possible to separate the hard disk into several partitions. In that way, you create several logical devices, from one bigger, physical device. There is a reserved space on the beggining of the hard drive device, called partition table. In that space, all information about the partitioning is stored.
There are a lot of reasons to separate your hard disk into partitions. In any way, the partitions enable you to store data more efficiently. For example, for PCs with multiple Operating Systems on, it is wise to install each OS on different partition.
When you separate your disk into partition, you don't store information in the partitions. Actually, you install filesystem on the partition and store files in it. The partitions are only used to separate your physical device into logical devices, understandable for you.
In many Operating Systems, the fdisk utility is available. Disk druide is always a common choice to some Linux users.
We will give example of partitioning a hard disk, using the fdisk utility. Let's assume that we want to create the following partition scheme:
/dev/hda1 Boot partition /dev/hda2 Swap partition /dev/hda5 Root partition
So, assuming that our main disk is '/dev/hda', we fire up fdisk:
Then, we get the command prompt:
Command (m for help):
From here, there are several possibilities. We can erase ALL disk partitions which have been already created, or we can just reformat them, as we need them. However, we can view the current partition scheme:
Command (m for help): p Disk /dev/hda: 280 heads, 65 sectors, 2400 cylinders Units = cylinders of 15150 * 512 bytes Device Boot Start End Blocks Id System /dev/hda1 1 14 105808+ 83 Linux /dev/hda2 15 49 264600 82 Linux /dev/hda3 50 70 158760 83 Extended /dev/hda4 71 2184 15981840 5 Extended /dev/hda5 71 209 1050808+ 83 Linux Command (m for help):
As you can see, in order to accomplish the starting idea, we must delete these partitions:
Command (m for help): d Partition number (1-4): 1
In this example, we delete the first partition, note that it is /dev/hda2. The second partition would be /dev/hda2 and so on. Repeat the procedure above to delete all of them.
Now, the partition table is empty. So, first we will create the boot partition, /dev/hda1.
Command (m for help): n Command action e extended p primary partition (1-4) p Partition number (1-4): 1 First cylinder (1-3967, default 1): (Enter) Using default value 1 Last cylinder or +size or +sizeM or +sizeK (1-3967, default 3876): (Enter or use +32M, it is enough for boot)
So, we check:
Command (m for help): p Disk /dev/hda: 30.0 GB, 30005821440 bytes 245 heads, 66 sectors/track, 3967 cylinders Units = cylinders of 15120 * 512 = 7741440 bytes Device Boot Start End Blocks Id System /dev/hda1 1 14 105808+ 83 Linux
Now, to create it as boot partition, we type 'a' in the command line, and select 1. Then, /dev/hda1 will be boot partition.
Now, we must create the swap partition. We defined it to be in /dev/hda2. So, we must first create it, just like the boot partition. Type 'n', then 'p', for primary partition, then select 2, for /dev/hda2. When prompted for first cylinder, hit enter, for the last cylinder select a size. It is prefferably to be big enough, for example 512 MB. You can create it bigger. However, for the last cylinder type +512M if you like so. Then type 't' in the command line to set a partition type. Then 2. For partition type, enter 82, which reffers to Linux Swap. After all this, check the table:
Command (m for help): p Disk /dev/hda: 30.0 GB, 30005821440 bytes 245 heads, 66 sectors/track, 3967 cylinders Units = cylinders of 15120 * 512 = 7741440 bytes Device Boot Start End Blocks Id System /dev/hda1 * 1 14 105808+ 83 Linux /dev/hda2 15 81 506520 82 Linux swap
Now, the last part, creating the root partition. It is pretty like every other partition we created so far. Type 'n' to create new partition,then 'p' for primary partition. Then , type 5, because we selected /dev/hda5 to be our root partition. Now, for both , the first and the last cylinder press enter, because we need to take as much space as we can. Check the results again, by hitting 'p':
Command (m for help): p Disk /dev/hda: 30.0 GB, 30005821440 bytes 245 heads, 66 sectors/track, 3967 cylinders Units = cylinders of 15120 * 512 = 7741440 bytes Device Boot Start End Blocks Id System /dev/hda1 * 1 14 105808+ 83 Linux /dev/hda2 15 81 506520 82 Linux swap /dev/hda5 82 3876 28690200 83 Linux
In order to recognize different partitions, when a specific partition is created, a special byte of data is added to it. By that byte, its partition type will be recognized. Here comes the table of partition numbers:
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 Tab
In the standard partition table, defined on the beggining of this document,there is space to record only four partitions. In other words, that means that only four partitions can be created on your HDD. But, to overcome this limitations, extended partitions were created. Every extended partition records partition information about the other partitions. Therefore, the possiblity opens to create more then four partitions.