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What is the maximum number of partitions we can make on hard disk in Windows?

If it is limited to some particular number, why can we assign all the letters C through Z to drives? If it is a special case, what's that?

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    The number of partitions per hard disk isn't relevant to the number of drive letters, since there may be more than one hard disk in a system. (Also drive letters are used for other things such as mapped network shares.) – Harry Johnston Dec 15 '11 at 20:41
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On the legacy "MBR" partitioning scheme, you can have 4 primary partitions, or 3 primary partitions and one extended partition containing any number of logical partitions. While you can assign a drive letter to a partition, you can also map it as a folder in current versions of Windows, allowing more partitions, or use subst to mount it to a number.

The EFI specification mandates that a GUID Partition Table (GPT), which all modern operating systems support, is capable of containing a maximum of 128 partitions on any size hard disk. GPT is also required to boot from hard disk drives larger than 2 TB. This partitioning scheme is now widely used with UEFI being natively supported by practically all new computers.

In addition to native partitions, Windows and Linux also have something called a "logical volume manager", which can overlay dozens, if not hundreds of virtual partitions (logical volumes) on top of the 4 (MBR) or 128 (GPT) physical partitions. Logical volumes can be assigned drive letters or mountpoints in the same way as physical partitions. They can also be bootable if certain constraints are met.

It's also possible to have GPT-formatted disks on non-UEFI systems, and MBR disks on UEFI systems (with the exception of the boot disk).

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    Isn't it the other way around? One extended partition containing any number of logical ones? – avakar Dec 15 '11 at 7:31
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    my bad ;p fixed – Journeyman Geek♦ Dec 15 '11 at 7:57
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    4 partitions is the MBR scheme. Other schemes are out there. – mouviciel Dec 15 '11 at 8:14
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    Ya, not gotten to play with GPT or BSD Slices yet. – Journeyman Geek♦ Dec 15 '11 at 8:17
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    @Steve314, you can remove Window's system maintenance partition and even prevent it from creating it. Also, both Linux and Windows can boot from logical partitions just fine, just the bootloader has to be on a primary partition (a small partition with GRUB will make that trivial). – Mircea Chirea Dec 15 '11 at 12:31
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On a disk using the traditional MBR format, the partition table has four slots. Each can hold a "primary" partition, or one can be used to create an "extended" partition which can contain any number of sub-partitions (often called "logical drives"). Extended partitions are basically a workaround for the small size of the MBR partition table, and there are limitations on what they can be used for. (For example, the Windows bootloader must be on a primary partition.)

The newer GPT disk format supports many more partitions — technically unlimited, I think, but operating systems impose a limit of 128. These are all "primary" partitions (to use the MBR terminology).

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  • I'm totally out of touch with GPT. Looks like i have some learning to do ;p – Journeyman Geek♦ Dec 15 '11 at 5:07
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From Technet: Reviewing Storage Limits: Local File Systems:

The number of disk drives you can use for each server is limited only by the available memory for FAT16, FAT32, NTFS, and UDF files systems.

So no there is no hard limit on Windows on the number of drivers. Drive letter are of course limited, since they stop at Z. But drives don't have to be given a drive letter - they can be mapped to a folder on another drive. From the same Technet article:

Mounted drives are useful when you want to add more storage to an existing volume without having to extend the volume. A mounted drive is a local volume attached to an empty folder on an NTFS volume. Mounted drives are not subject to the 26-drive limit imposed by drive letters, so you can use mounted drives to access more than 26 drives on your computer. For more information about mounted drives, including information about creating mounted drives on server clusters, see "Using NTFS mounted drives" in Help and Support Center for Windows Server 2003.

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    4 upvotes, and it doesn't answer the Qs!? The question is about partitions not drives. – sawdust Dec 15 '11 at 6:09
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    actually original question title said drives, it was edited to partitions, since , well, considering context, it was more correct. – Journeyman Geek♦ Dec 15 '11 at 8:17
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Hard disks can be split into four primary partitions, or one of these can be configured as an extended partition.

An extended partition can theoretically contain an infinite number of logical partitions, and so while Windows only has drive letters up to z: (plus some other characters) this is not a limit on the number of partitions you can create, even if you can't assign a drive letter to them.

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    While this is true for disks with an MBR partition table, this is incorrect for disks with a GPT partition table. – Darth Android Dec 15 '11 at 3:56
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If the drive is partitioned using GPT, windows can only handle 2 for the following reason. When GPT is employed, each primary partition has another hidden partition to go with it called EFI. When Windows sees this EFI partition, it counts as 1 primary. So 2 partition in GPT means 4. This is a sad limitation for Windows when testing a new build using GPT scheme. Linux and OS X is far more flexible.

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Maximum slices allowed on windows mbr is 4.

Loosely called as "partitions", means 4 paritions. However, any one of these 4 partitions, ie one and only one of them can be extended further into "partitions" or logical drives. In summary, it is said as 3 primary partitons and one "extendable" partition. The "extendable" partition as logical drive can only go with the letters a to z. As the alphabet a and b are used for floppy drives, only c to z is available for use.

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  • Drive letters do not limit the number of partitions Windows can handle. You can mount volumes as directories under other drive letters. – Ben N Feb 21 '16 at 23:57
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Theoretically, an unlimited number of partitions can be created in a drive. The total number of partitions is limited by the amount of space that is reserved for making partition entries.

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  • -1 for being quite wrong. The theoretical limits are calculable with some simple arithmetic and are very much finite. – JdeBP Dec 23 '11 at 11:15

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