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I would like to know

What is the exact meaning of primary partitions? Why it is named so? and why it is restricted to 4?

What is meant by extended partitions? Why it is named so? and what is the possible number of extended partitions in the hard disk?

What is mean by logical partitions? Why it is named so? How it is calculated?

What are the advantages of these software partitioning?

Is it it possible to install OS(Linux/windows) in all partitions ? If no, why?

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Please don't moderator flag questions because it doesn't get answers. The moderators have no influence on questions getting answered. –  Diago Oct 21 '10 at 7:20

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up vote 6 down vote accepted

The "MS-DOS" partitioning scheme is limited to 4 primary partitions. This is all that will fit in the first sector (512 bytes) of the disk after the MBR (460 bytes).

In order to have more than 4 partitions, one of them becomes an extended partition, which points to an extended structure further down the disk. This structure lists the logical partitions on the disk.

The "legacy" MBR uses one of the flags on the primary partitions to determine which to boot up; this flag does not exist on logical partitions, so they cannot be booted the same way. Other MBR replacements (e.g. GRUB) do not use this flag and so can boot logical partitions.

Theoretically, any OS can be installed to either primary or logical partitions, but older versions of Windows will not boot properly if not installed to a primary partition.

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Can you little bit deeper ? that is about the first boot sector-- 512 bytes? among that 460 bytes MBR then 52 bytes for 4 partitions? how the logic behind that? The first boot sector(512 bytes) also in the first primary partition right? How we configure the 52 bytes for 4 partitions? Why MBR takes 460 bytes , what it contains? –  Renjith G Oct 15 '10 at 22:50
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The legacy MBR contains the logic needed to detect which of the 4 primary partitions has the boot flag set as well as the instructions needed to tell the computer to load from that partition and start it. 13 bytes was all that was needed for each partition, so that's what they gave them. They figured 4 partitions would be plenty, so they let the MBR have the rest of the space. –  Ignacio Vazquez-Abrams Oct 15 '10 at 22:54
    
not at all clear! :-( .... there should be a superb bit logic behind that! –  Renjith G Oct 15 '10 at 22:58
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It was logical at the time they invented the 512 boot sector, they never figured anyone would need more partitions at the time, kind of like tcp/ipv4, the never figured we would ever need more addresses at the time, but we do now! –  Moab Oct 16 '10 at 18:01
    
Ok. But i want the bit division logic of that 512 bytes boot sector ! –  Renjith G Oct 18 '10 at 4:16

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