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What are the major differences? Which is more preferable? Are there any OS specific advantages for one over the other?

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You can have only 4 primary partitions (3 if you decide to have an extended partition), whereas you can have an arbitrary number of logical partitions. There are no OS-specific advantages other than older versions of Windows must be installed on a primary partition and that the legacy MBR bootloader can only boot from a primary partition.

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In the legacy MBR partition scheme, only at most four partitions can be created (they are called "primary" partitions). To bypass this limit, one of the entries is usually made an "extended" partition – instead of files, it contains several "logical" partitions.

MBR: < primary | primary | primary | primary >

MBR: < primary | primary | extended [logical, logical, logical] >

In practice, the only difference is that some operating systems (namely Windows) are unable to boot from logical partitions.

A newer partition scheme, GPT, is used on some recent systems, including all Intel Macs – it doesn't have such small limits, and does not need to use extended/logical partitions.

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Note that you don't need to have 3 primary partitions before you can create an extended partition... or indeed any primary partitions at all. – Ignacio Vazquez-Abrams Sep 18 '11 at 21:11
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they're not alternatives, it's more a point about the order you create them and their hierarchical relationship. The first is called the primary partition. Some OSs let you have more than one. Within any (In addition to any) Primary you can create an extended partition, and if you want more partitions, then within the extended partition you can also create logical partitions.

thanks to grawity and ignacio for corrections.

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Primary partitions always contain data, never extended partitions (primary and extended are on the same hierarchy level), their count is not OS-dependent, and the order doesn't matter. – grawity Sep 18 '11 at 21:01
@grawity no relationship between primary and extended then? I see.. and just read on wikipedia, a hdd can only have one extended partition. So I suppose if one wants multiple partitions, one would just create multiple primary partitions if possible, then if they need more, they'd create an extended partition to go along with the primary one(s), and if more then logical within that extended one. Is that right? – barlop Sep 18 '11 at 21:06
Yes, that's right. (Except it only applies to MBR-partitioned disks, but other types such as GPT exist.) – grawity Sep 18 '11 at 21:08
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@barlop: Mostly correct, except that the single extended partition restriction is due to assumptions by the OS rather than any physical or logical limit. – Ignacio Vazquez-Abrams Sep 18 '11 at 21:10
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Actually, multiple extended partitions does have a use. It was used by some people to separate the secondary partitions that they didn't want operating systems such as MS/PC-DOS and OS/2 to see from those that they did. This was done by having two container partitions, one with the conventional 0x05 type and the other with a non-standard 0x85 type. Andries Brouwer wrote about such systems years ago. – JdeBP Sep 20 '11 at 22:42
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Primary partitions have entries in MBR. So, there are maximum 4 primary partitions and one of them may be extended partition. The extended partition can contain variable number of logical partitions. The extended partition contains VBR by which Program control can get the information of logical partitions.

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