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I remember reading somewhere that as opposed to the former versions of Windows - more than 4 can be created, but I can't seem to find it on the web now. Is this true?

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6 Answers 6

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Strictly speaking, Windows only ever allows 4 primary partitions, because the phrase "primary partition" is only applicable to MBR partition tables and MBR partition tables only allow four primary partitions.

However, if you use a GPT partition table (available since Windows Server 2003 on 64-bit versions of Windows) you can have up to 128 partitions and do not need to distinguish between "primary" and "extended" partitions.

Depending on your computer model, you might not have the option of using a GPT partition table on your boot disk, because Windows only has native support for booting GPT disks via UEFI, not via BIOS.

What changed with Windows 8 is that computers sold with Windows 8 must (in order to be certified) support UEFI booting. They must also ship configured to UEFI boot; as a consequence of this they must be shipped with GPT partition tables.

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"Windows only has native support for booting GPT disks via UEFI, not via BIOS" - This is only for consumer versions of Windows, right? Some server versions (for Itanium specifically) don't seem to have the UEFI requirement to boot from GPT disks as per Wikipedia. Do you know if that's true and these versions can indeed boot from GPT disks without UEFI, just as Linux can? –  Karan Mar 6 '13 at 18:10
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@Karan: Itanium is an entirely different kettle of fish, and my answer certainly wasn't intended to apply to it. According to Wikipedia, Itanium uses EFI (the predecessor to UEFI) exclusively, i.e., there's simply no such thing as booting via BIOS on Itanium. –  Harry Johnston Mar 6 '13 at 21:00
    
I know your answer wasn't about Itanium; I just wanted some info on Windows support for GPT booting via BIOS. Seems you're right about the Itanium using EFI, so thanks for clearing that up. –  Karan Mar 6 '13 at 22:13

The number of primary partitions isn't a limitation of the operating system, but of the partition table.

gptgen is able to convert an MS-DOS partition table into a GPT:

Gptgen is a tool to non-destructively convert hard disks partitioned in the common, "MSDOS-style" MBR scheme (including extended partitions) to use a GUID partition table (GPT).

I haven't tried the tool myself, but I found a few success stories on Google. Keep in mind that any modification of the partition table carries the risk of data loss.

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Thanks. So can I change from one to another? –  ispiro Mar 5 '13 at 13:41
    
I've edited my answer. –  Dennis Mar 5 '13 at 13:45
    
It is my understanding that, at least for the disk containing the boot partition, you must use a MBR partition table if you are booting via BIOS and you must use a GPT partition table if you are booting via UEFI. (At least, Windows setup enforces this requirement; there may be tricks you can use to bypass it.) –  Harry Johnston Mar 5 '13 at 22:22
    
@HarryJohnston It seems that that was what I read. Thanks to your comment I searched and found that new computers that want to be Windows-8-certified (or something like that) must use UEFI. You can convert your comment into an answer. Thanks! –  ispiro Mar 5 '13 at 23:12
  • You can have maximum of either 4 primary partitions or 3 primary partitions and one extended partition containing any number of logical partitions. If you don't have enough drive-letters to assign (A: B: C:...), you will have to mount the partitions as NTFS folders.
  • Windows creates a small system partition (a few hundred MB) for recovery, boot and system data.
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You could have more than 4 partitions far before Windows 8.

However, you can have up to 4 primary partitions or up to 3 primary partitions plus extended partition to hold logical drives (which are informally called "partitions" too). Those will work just as primary partitions in Windows.

Note that extended partition can't hold data itself, but logical drives do.

4 primary partitions is a limitation of MS-DOS partition table.

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Once BIOS detects the bootable device then it executes the MBR (Master Boot Recorder). MBR is 1st sector (512 Bytes) of the 1st bootable device. In 512 bytes, 3 parts are there :

i. 1st 446 bytes has primary boot loader information.

ii. Next 64 bytes for Partitions (16+16+16+16) for this reason only we are able to make 4 Primary Partitions.

iii. Next 2 bytes for validation check of MBR. (Magic Number)

Only one of the four partitions can be marked as active. Second boot loader is then loaded from 1st sector of this active partition which gives you an option to chose your OS to boot.

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With the standard bios/MBR method you can have 4 Primary partitions, however this is not a good idea if you may want to add futher partitions later. Windows will automatically make the fourth partition an extended one, this ensures that you can add more partitions (space permitting) if required in the future, only one partition can be active and for DOS based systems (including W95/98) this must be the first partition.

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As Windows 7/8 use a different method of booting it is possible to have 128 as mentioned previously. –  John Aug 11 '13 at 22:44

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