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[ The PC Guide | Systems and Components Reference Guide | Hard Disk Drives | Hard Disk Logical Structures and File Systems | New Technology File System (NTFS) | NTFS Architecture and Structures ]

NTFS Partitions and Partition Sizes

NTFS partitions are very different from FAT file system partitions on the inside--in terms of their structures and how they function. However, externally, they conform to the general rules that apply to all partitions. This is necessary to ensure that the PC boot process can handle an NTFS partition in pretty much the same way that it does a FAT partition. Therefore, like FAT partitions, you can have primary or logical NTFS partitions, and logical NTFS partitions fit within an extended partition. You can find more information about these terms and the rules for partitions on this page.

Since NTFS was designed from the start to be a file system suitable for use in corporate and business environments, it is no surprise that the file system allows very large partitions to be created. Recall that at the time Windows NT was released, the only versions of FAT that existed were FAT12 and FAT16--FAT32 had not yet been created. The maximum partition size of FAT16 under Windows NT is 2 GiB using 32 kiB clusters, or 4 GiB using the non-standard 64 kiB clusters that other versions of Windows do not support. Considering the large storage needs of businesses, and also considering that many businesses servers use RAID to create even larger volumes, such small size limits would have been completely unacceptable in NTFS, even a decade ago when NTFS was being developed.

Under NTFS, the maximum size of a partition (volume) is in fact 2 to the 64th power. This is equal to 16 binary exabytes, or 18,446,744,073,709,551,616 bytes. Does that seem large enough for your needs? :^) Well, many problems with PC hard disks occurred when unintentional size limits were imposed by engineers who figured that, for example, "2 gigabytes ought to be enough". However, with 18 billion gigabytes it would seem that you should be safe for a while in NTFS. :^)

Then again, it always pays to be careful when looking at such huge numbers. For example, I pointed out elsewhere that FAT32 claims to be able to support up to 2 TiB partitions, but does so at the cost of tremendous slack waste and an enormous file allocation table. NTFS is a completely different file system, but since it was designed at a time when hard disk sizes were measured in single gigabytes, there's no real way to know how well it will scale to disk volumes that are thousands or even millions of gigabytes in size. I suppose we will get there in due time, but as the paragraph below explains, there are already provisos on these large volume limits.

Under Windows NT there are significant restrictions imposed on the size of the boot partition--the first partition on the drive. During installation, Windows NT always first creates a FAT16 partition. Even if you tell NT that you want to install to an NTFS partition, it first creates a FAT16 partition and then converts it to NTFS. Since the maximum size of a Windows NT FAT16 partition is 4 GiB, this limits the size of your boot partition as well. Even if you use a third-party tool to increase the size of the partition, you run into another limitation: Windows NT can't boot from a partition larger than 7.88 GiB period, regardless of how you create it (this is associated with Windows NT's older design, which predates the implementation of the Int 13h Extensions required for large hard disk access).

Due to these limitations, many NT setups use at least two partitions--a smaller one for the operating system and a larger one for applications and data. Many people find this a good way to set up the disk anyway, as it keeps operating system files separate from others. These boot size limit problems have been eliminated in Windows 2000. You can format and use an entire large hard disk in a single partition under Windows 2000.

Tip: I have a full page on partitioning strategies under NTFS in the section on implementation.

Note: BIOS issues associated with IDE/ATA hard disks can impose partition size limits irrespective of the operating system or file system. In particular, support for IDE/ATA hard disks over 7.88 GiB requires a BIOS with support for Int 13h Extensions. See here for more details.

Next: NTFS Clusters and Cluster Sizes


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