What is the difference between a primary partition and an extended partition?

Answer 1

Taken from: http://www.pcguide.com/ref/hdd/file/structPartitions-c.html In order to use the space in a hard disk, it must be partitioned. Partitioning is the process of dividing the hard disk's space into chunks, so they can be prepared for use, or even dedicated to different uses. Even if the entire disk is intended to be left in one piece, it must be partitioned so that the operating system knows that it is intended to be left in one piece. There are many different considerations that go into deciding how to partition a hard disk. The rules that determine how partitions are used were set down very early in the original design of the PC, and have remained virtually unchanged since that time. Recall that when the PC was first invented there was only (really) one type of file system. Still, it was envisioned that in the future, multiple operating systems and/or file systems might be wanted on a single machine. Therefore, provision was made in the partitioning scheme to allow for several different partitions. The rules that govern partition setup are as follows: A maximum of four partitions can be placed on any hard disk. These are sometimes called primary partitions. The limitation of four is one that is imposed on the system by the way that the master boot record is structured. Only one partition may be designated, at any given time, as active. That partition will be used for booting the system. See here for more on active partitions and switching active status between partitions. DOS (and the operating systems that depend on it for booting, which includes all consumer Windows operating systems) will only recognize the active primary partition. Any other primary partitions will be ignored. One of the four partitions may be designated as an extended DOS partition. This partition may then be subdivided into multiple logical partitions. This is the way that two or more logical DOS volumes can be placed on a single hard disk. Alright, I realize that this is somewhat confusing, so let's take a look at some examples of systems, to show you how this scheme is used: Single Partition Windows PC: Many PCs have all of their disk space made into a single partition, and use one of the FAT file systems. Such a machine would have just a single FAT primary partition on it, and nothing else. The other three "slots" for partitions on the disk would be empty. Multiple Partition Windows PC: To use more than one partition at a time on a DOS/Windows system, two partitions are used. One is a regular DOS primary partition (which becomes the "C:" drive). The other is the extended DOS partition. Within the extended DOS partition, all the other logical drives are created. So a drive with four logical drive letters would have the first (C:) be the active primary partition, and the other three (D:, E: and F:) would be logicals within the extended DOS partition. Multiple Operating System PC: A system with multiple operating systems could use one primary partition for each of up to four different file systems. If you want, you can also combine multiple partitions with multiple operating systems. For example, you could have a primary DOS partition, an extended DOS partition, and a Linux partition. Such setups are far less common than the simpler examples above. The extended DOS partition causes most of the confusion on the part of those setting up new DOS/Windows PCs. It really functions as a "container" that holds all DOS partitions except for the first (primary) volume. The reason that this structure was used is that the original design, with its limit of four partitions, was too restrictive. The extended DOS partition system allows you to have up to 24 disk partitions in a single system, without violating compatibility with older hardware and software designed based on the original four-partition limit. Of course, nobody would use that many partitions on a system in most cases, because it would be a data organization nightmare! :^) Within the extended DOS partition, the logical drives are stored in a linked structure. The extended partition's information is contained in the master partition table (since the extended partition is one of the four partitions stored in the master boot record). It contains a link to an extended partition table that describes the first logical partition for the disk. That table contains information about that first logical partition, and a link to the next extended partition table which describes the second logical partition on the disk, and so on. The extended partition tables are linked in a chain starting from the master partition table. In terms of how the disk is used, there are only two main differences between a primary and a logical partition or volume. The first is that a primary partition can be set as bootable (active) while a logical cannot. The second is that DOS assigns drive letters (C:, D: etc.) differently to primary and logical volumes. Here's an example to hopefully make all of this a bit more clear. Let's suppose you are setting up a new system and starting with an empty 60 GB hard disk. You could create a single 60 GB partition, which would be a primary DOS partition. However, in many cases dividing up such a large disk will make it easier to manage the space, will reduce lost disk space due to slack, and will reduce defragmentation time on partitions containing more actively-used data. (See here for much more on the issues involved in partitioning.) So instead, let's say you want to split up this drive as follows: One 8 GB primary partition for Windows and other operating system and program files. One 12 GB partition for data. One 16 GB partition for games. The rest of the disk in a 24 GB partition for large multimedia files, short-term backups and "future expansion". I'm assuming no complicating factors here, just a simple example. To do this, you will first set up a primary DOS partition 8 GB in size. This is the first of your four partitions. You will then create an extended DOS partition that is 52 GB in size. This is the second partition on the hard disk. Within the extended DOS partition you will create three logical volumes: one 12 GB, one 16 GB and one 24 GB. These are your second, third and fourth volumes (logical partitions). The first partition will be your C: drive from which you boot the machine, and DOS will (normally) assign D:, E: and F: to the other three logical partitions. Your hard disk will have one primary DOS partition, and one extended DOS partition containing three logical DOS volumes.
A primary partition can have an operating system installed on it (eg: Windows XP). Most computers only have one primary partition. The limit is four. To get around this limit, one primary partition can be traded for an extended partition. This extended partition can be split into logical drives. All of these drives will show up to a regular user as being the same.

Answer 2

Primary partition is like main entrance of your house. When the operating system boots (starts up) it has to access your primary drive and RAM to load operating system. Extended partitions are the fractions separated from primary drive for data storage purposes.

Answer 3

A Primary partition, as the name implies, is the first and most important. A drive can be just one big primary, and nothing else. Primary partitions have a small boot section formatted onto them, which the OS will use for finding the rest of itself, to be able to load up. They also contain the Partition Table, which describes how the drive is divided up.

Extended partition is the other part of the drive, but some systems allow more than one extended one. These generally cannot be used for booting the computer.

Logical drives can be in either type of partition. They are like a real drive in logic (the way they function), but not physically.They cannot be booted from. They are a kind of "super-folder" with their own filing system for tracking folders and files on them. Splitting a large drive into many logicals, for different types of data, can speed up access to the data, as there are smaller indexes to look up each time.

Most hard drives that come with a computer are only partitioned into primary and extended, the latter containing a mirror or backup of the most important system files. These could then be known as C: (primary) and D:

You can add logicals from E: through to Z:

Windows after Win98 let you give permanent letters to partitions; before that they would be assigned dynamically, so if you disabled your CD, the other letters above it (eg USB thumb drive) would slide down by one.

Answer 4

In the days of MS-DOS, Microsoft deemed that no single hard drive would ever need more than four file systems at once. So in order to make things simple, Microsoft only gave hard drives the capability to hold 4 partitions (at this time they were simply called 'partitions', instead of their modern term 'primary partitions')

However, there came a need for drives with more than four partitions. What Microsoft did is they added the ability to add a second partition table. In order for MS-DOS to remain backwards compatible, they placed this second partition table in a place pointed to by the the fourth partition of the original table. This new 'extra partition table' is called an Extended partition, and it acts like a container for additional partitions which can fit inside of it (called Logical partitions)

In this way it's possible to have more than 4 partitions by having 3 primary parititions as well as an extended partition which can contain several logical partitions which will also show up as drives on your computer.

Answer 5

David is partially correct. Yes, we are talking about terms from back in the days of MS-DOS, DR-DOS, and PC-DOS. However, the terms of Primary, Extended, and Logical Partitions were used in those forms. The Primary partition was the first partition on the drive and was the only bootable partition on the drive. The Extended partition was the partition that consumed the rest of the drive. Traditionally, the largest hard drive that could be used was 30 megabytes. So, if one had a 120 megabyte hard drive such as the Seagate ST4144R (an RLL hard drive that was the cousin of the Seagate ST4096 MFM hard drive which had a capacity of only 80 megabytes), one would make a primary partition formatted as bootable under DOS and sized up to 30 megabytes and then the rest of the drive would be created as an extended partition that could be chopped up into usable partitions of up to 30 megabytes in size each. The only restriction was that there could be no more than 23 logical drives since that would consume the rest of the alphabet D: through Z:. (CD-ROM drives were not common back then as they were still in their infancy, so no drive letters were reserved for them but A: and B: were still reserved, and at least A: was often used for the floppy drive.)

Back when I was still using MS-DOS 6.22 around 1993, I had a Maxtor 7546A IDE hard drive that had about 540 megabytes of storage and, though I could have used larger partition sizes by that time due to improvements that had come to DOS by then, I still kept the partitions at 30 megabytes each for most efficient use of the space. (This has to do with the cluster size that is used by the system to allocate hard drive space, a topic that is not germane to this answer, so if anyone is curious, feel free to drop me a line and I will explain.) As such, I had eighteen drives on the machine with C: being the boot drive/Primary partition and drives D: through T: being for data, installation of programs and games, and for keeping my wife out of the projects on which I was working. (She had a habit of deleting files she didn't recognize, such as anything that had an extension of .pas or .c)