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There is always a lot of confusion about partitions and partition numbers. So let us try to shed some light:

There are three types of partitions:
  1. Primary Partitions 
  2. Extended Partitions 
  3. Logical Partitions 
Primary and extended partitions are the main disk divisions; one hard disk may contain up to four primary partitions, or three primary partitions and one extended partition. The extended partition can then be further divided into any number of logical partitions.

The illustration below shows a hard disk that contains four main partitions: three primary partitions and one extended partition. The extended partition has been further divided into two logical partitions. Each primary partition has been formatted to use a different file system (FAT and NTFS). The two logical partitions have both been formatted to use the FAT file system. 

Primary Partitions

A primary partition may contain an operating system along with any number of data files (for example, program files, user files, and so forth). Before an OS is installed, the primary partition must be logically formatted with a file system compatible to the OS.

If you have multiple primary partitions on your hard disk, only one primary partition may be visible and active at a time. The active partition is the partition from which an OS is booted at computer startup. Primary partitions other than the active partition are hidden, preventing their data from being accessed. Thus, the data in a primary partition can be accessed (for all practical purposes) only by the OS installed on that partition.

If you plan to install more than one operating system on your hard disk, you probably need to create multiple primary partitions; most operating systems can be booted only from a primary partition.

Extended Partitions

The extended partition was invented as a way of getting around the arbitrary four-partition limit. An extended partition is essentially a container in which you can further physically divide your disk space by creating an unlimited number of logical partitions.

An extended partition does not directly hold data. You must create logical partitions within the extended partition in order to store data. Once created, logical partitions must be logically formatted, but each can use a different file system.

Logical Partitions

Logical partitions may exist only within an extended partition and are meant to contain only data files and OSs that can be booted from a logical partition (for example, Linux, Windows NT, and so forth).

On an IDE drive, the first drive is called hda, and the partitions are shown as hda1, hda2 . . . . etc. etc. Your second drive is called hdb.

On a SCSI drive, the first drive is called sda, the partitions are sda1, sda2 . . The second drive is called sdb. 

Now that was relatively simple, but now comes the more complicated part, I took parts of this from a post of Jason Wallwork ( Linuxdude32 ) because he was able to explain it better then I can:

An extended partition is the only kind of partition that can have multiple partitions inside. Think of it like a box that contains other boxes, the logical partitions. The extended partition can't store anything, it's just a holder for logical partitions. 

The extended partitions is a way to get around the fact you can only have four primary partitions on a drive. You can put lots of logical partitions inside it. 
  • hda is the whole drive
  • hda1 is a primary partition
  • hda2 is a primary partition
  • hda4 is an extended partition
  • hda5 is an logical partition
  • hda6 is an logical partition
You will never see hda4 mounted, just hda5 and hda6, in this case. Note that Linux numbers primary partitions 1-4, logical partitions start at 5 and up, even if there are less than 4 primary partitions.

NOTE: On an IDE drive you can have up to 63 partitions, 3 primary and 60 logical ( contained in one extended partition ) 

On a SCSI drive the maximum number of partitions is 15 

So, in a nutshell: if you start out with one HD that has windows C: and D: You will see them in Linux as hda1 and hda2 . . . then as you add a distro and let it automatically use the free space on that drive ( if that distro has that option like Mandrake ) it will make an extended partition and set up a partition for / and a partition for /swap plus a /home partition and call them hda5, hda6 and hda7 ( in that order ). You will see that if you make the partitions yourself, using preferably a Linux tool to make the partitions, the result will be more or less the same, only in that case you will be able to make even more partitions . . . for extra storage, backups, or additional distros 

You will only need one swap partition as that can be shared by the various distros. 

Oops, I forgot:

May I suggest using one partition for the OS(active primary) and the rest will reside in an extended(primary) as logical partitions. The extended partition will be hidden(this doesn't matter, as it's only the container for the logicals), but all of the logical partitions will be visible. 
I hope this makes sense.


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