Primary vs. Extended Partitions

What is the difference between a Primary and Extended Partition? What is the rational of having an Extended Partition? What I am getting at is why just with stick with Primary. If Primary can do the job, why do you need Extended?

 

Be advised this is a very basic answer (and I'm sure other members will have more to add).

Primary partitions are used to boot an OS from - there's a limit to how many of these you can have (I think 4), and you typically only have one.

You can only have one extended partition and within it you can have as many logical drives as there are letters to assign (limited of course by available disk space).

It can be a whole lot more complicated than that, but hopefully you get the idea.

 

So with the extended partition, it makes your hard drive looks bigger to the OS in terms of storage?

 

Here is a more detailed description if you want to read more.

http://pcguide.com/ref/hdd/file/structPartitions-c.html

 

But if the primary partition is saturated with data, will the extended partition come in & compliment the primary partition, or will the OS will report a not enough space error to the user?

 

I think you're correct. But if you were partitioning your drive in this way then it would probably be to separate content such as media and programs from the system files on the main primary partition? So running out of space would be unlikely unless you didn't allow enough space for the system on your primary partition.

 

So having an extended partition is just like having another physical harddrive? When you partition, why just go like for example, NTFS, then your other partition should be NTFS, instead of NTFS and then extended? If extended is not use to compliment a saturated primary partition, then what is the point of having an extended partition. I know that the primary has only 4 tables and the first table is used to boot up the OS (Master Boot Record), but instead of having naming the other partition extended, just name it NTFS, FAT 32, or ext2 or ext3? There is no point in having an extended partition, I think.

 

Yes, and then it can be split in to more logical drives (effectively - they will be seen by Windows as other hard drives, e.g. G: H: J: etc).

I'm not sure why you're mentioning filesystem types, that's a separate topic surely.

An extended partition counts as one of your four primary partitions, but has the ability to be split in to logical drives.

So, for example, say you want separate logical drives for data, programs, music, pictures, videos etc - you already have more than 4 possible partitions there, so they could not all be primary partitions and thus requires you to use an extended partition.

 

So, did the last two replies help your understanding?

 

So how about the Linux side? How do partitioning works on the Linux side? The same way on the DOS side?

Here is a peice of an example of how my hard drive looks like.

Device Boot Start End Blocks Id System
/dev/sda1 * 2048 23070719 11534336 12 Compaq diagnostics
/dev/sda2 23072766 312580095 144753665 5 Extended
/dev/sda5 23072768 26976255 1951744 83 Linux
/dev/sda6 26978304 42600447 7811072 82 Linux swap / Solaris
/dev/sda7 42602496 312580095 134988800 83 Linux

Can someone explain this,especially /dev/sda2? I have Ubuntu verison 12.04 LTS

 

I know very little about the proper workings of Linux filesystems, but below are a few basics off the top of my head..

'sda' refers to the main HDD. If you had another drive mounted, it would be 'sdb', and so on. The number refers to an individual partition on that drive. Numbers 1 to 4 are reserved for primary partitions (whether or not they exist) and logical drives start at 5.

Your partition sda2 is apparently an extended partition, which would make sense as it is the largest. Linux makes use of logical drives within an extended partition for things like /home and /tmp.

Linux also has something called a 'swap partition' (in your example sda6) which is virtual memory. It's essentially the same thing as the page file in Windows.

I suggest you Google for more information on this topic though, it's a lot more complex.

Edit:

So, to clarify, you have two primary partitions - sda1 and sda2. sda5, sda6 and sda7 are logical drives contained within your extended partition sda2. To the best of my knowledge anyway.

 

The link will give a decent understanding of why extended is required & what it actually is,turns out it's nothing more than a link to the space that comes after it is the way i read it,i'm still pondering what the issue is

http://pcguide.com/ref/hdd/file/structPartitions-c.html

 

I already read this link. I found it to be very educational. Especially one pararagraph that implies that all logical drives link themselves up with the primary drive like a chain. Each logical drive pointing itself to the the primary drive. It also says that you can have up to 24 partition in partition in a single system.

I am beginning to understand the concept of logical vs primary in the terms of DOS where primary is where the OS resides, and the extended is just use for storage of miscellaneous items like media files, docs, or applications. Since an OS is not an AI, it only do what the user wants it to do.So basically you have to tell the OS to store your items in the logical section of the drive.

 

In the terms of Linux, what I am getting from you Ripper is that the OS uses sda2 to write it's files like /home, /proc, /usr, /tmp, /bin, and etc.This means that any application that is new, Linux would write it in sda2 in one of the following files.

I like this method because it sound like Linux would take the initative to write in that sector instead you tell it where to write. It sounds like Linux does a lot of activity in sda2.