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In the image below, what does Extended 103 GB mean?

screenshot of Disk Utility showing a 500 GB drive with two primary & one logical partition

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On systems without Windows, I have no primary partitions at all. for a new disk, I create one big extended partition the full size of the drive, then create logical drives inside that. But Windows wants to be in a primary partition. I know of no downside to exclusive use of extended partitions. – Marty Fried Jun 17 '12 at 5:15

A traditional partition table like yours can have maximum of four primary partition. That means you can't have more than four drive. Concept of extended partition solves this problem.

An extended partition is a special type of partition that can hold multiple logical partition. It's is like a container/wrapper of all logical partition. Inside extended partition you can create many logical partition (there solves the drive limitation).

Primary partitions generally used for installation of operating system. However logical partition can also be used. (like your ubuntu is installed in extended partition)

In your hard disk you have three primary partition

  • Windows (385GB)
  • Extended partition (where ubuntu is installed)
  • Recovery partition.

In a word, your partition table is 100% alright. :)

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Yes, using an Extended Partition is safe. It is a work-around used to extend the original method of partitioning a disk which only allowed dividing a disk into a maximum of four partitions. This description in Wikipedia provides a (very) brief overview of the terms and their meanings.

The original method was developed in the early 1980's when 10-20 MiB was considered a "very large" disk. To put it another way, the original Master Boot Record (MBR) partitioning scheme was created at a time when 0.002% of your 500 GB drive was considered a HUGE! amount of storage.

By the time they realized how foolish the original scheme was, they were locked into into it. So using an Extended Patition containing logical partitions was developed as a work-around.

At some point in the future, disks will no longer use MBR partitioning. Instead they will use a GUID Partition Table (GPT). Using GPT partitioning there can be (at least) 128 primary partitions. So GPT partitioning does not use an Extended Partition. (As a side note, a minimum of 16 MiB ... or over 1 1/2 times the size of one of those early 10 MiB hard drives used with a 1980's PC ... is reserved just for a GUID Patition Table.)

However, all the major computer manufacturers appear to be working together to make the transition from MBR to GPT partitioning as difficult as possible. So it is not clear at what point MBR partitioning will be replaced by GPT partitioning. The use of an Extended Partition may be with us for quite some time yet.

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