Understanding File System Options

Understanding File System Options

July 24, 2003

A file system, also referred to as a file management system or filesystem, is exactly what its names implies -- the mechanism an operating system or program uses to organize and keep track of files. The files systems most commonly used with Windows operating systems are the File Allocation Table (AKA FAT) and NTFS. FAT is available in two versions, FAT16 and FAT32.

FAT16 File Systems

The File Allocation Table (commonly known as FAT or FAT16) is supported by Windows Server 2003 as well as all Windows operating systems, DOS, and a host of other non-Microsoft operating systems.

FAT partitions are allocated in clusters, the size of which varies automatically based on the size of the partition in use. The larger the partition, the larger the cluster size; the larger the cluster size, the more space "required" when writing data to the disk.

FAT File System Cluster Sizes
Partition Size
Cluster Size
FAT Type
0 MB - less than 16MB 4,096 bytes 12-bit
16 MB - 128MB 2,048 bytes 16-bit
128 MB - 256 MB 4,096 bytes 16-bit
256 MB - 512 MB 8,192 bytes 16-bit
512 MB - 1024 MB 16,384 bytes 16-bit
1024 MB - 2048 MB 32,768 bytes 16-bit

As you can see, with a 2 GB partition size (the maximum allowed under FAT16 in many cases), if you were to save 50 different files, all 1024 bytes (1 KB) in actual size (or to have 50 fractions of larger files "fall over" to the next cluster by that same amount), the amount of hard drive space used up would be 1,638,400 bytes (a little more than 1 MB) for 51,200 bytes of actual data.

This becomes a serious problem when there are thousands of small *.DLLs and other types of small files on a partition formatted with FAT16.

The advent of super-inexpensive hard drives 100 GB or larger in size also makes using FAT16 an issue.

There are, of course, "advantages" of using the FAT file system:

  • MS-DOS, Windows 95, Windows 98, Windows NT, Windows 2000, and some Unix operating systems can all use FAT16. When dual-booting a system, FAT16 allows the greatest number of options.
  • Many software tools address problems and can recover data on FAT16 volumes.
  • If you have a startup failure, you can start the computer by using a bootable floppy disk to troubleshoot the problem.
  • FAT16 is efficient, in speed and storage, on volumes smaller than 256 MB. (e.g., those 50 files I mentioned above, all 1,024 bytes (1 KB) in actual size, would consume "only" 409,600 bytes on a 400 MB partition formatted with FAT16 and "only" 204,800 bytes on a 250 MB partition.

FAT16 brings with it disadvantages as well:

  • The root folder (usually the C:\ drive) has a limit of 512 entries. The use of long file names can significantly reduce the number of available entries.
  • FAT16 is limited to 65,536 clusters, but because certain clusters are reserved, it has a practical limit of 65,524. The largest FAT16 volume on Windows 2000 and Windows XP Professional is limited to 4 GB and uses a cluster size of 64 KB. To maintain compatibility with DOS, Windows 95, and Windows 98, a volume cannot be larger than 2 GB. (Those 50 files mentioned above, all 1 KB in actual size, would use up 3,276,200 bytes of hard drive space to store 51,200 bytes of actual data on a 4 GB FAT16 partition used in this scenario.)
  • FAT16 becomes inefficient on larger volume sizes, as the size of the cluster increases. This was the case in the two previously cited examples.
  • The boot sector is not backed up on FAT16 partitions. Because FAT16 does not include a backup copy of critical data structures, they are susceptible to single point of failure issues, more so than other file systems.
  • FAT16 has no native file level security, compression or encryption available in the FAT16 file system.

Below is a table of Microsoft operating systems and the file systems those operating systems can natively access.

Operating System
Window Server 2003 Yes Yes Yes 4 GB
Windows XP Professional Yes Yes Yes 4 GB
Windows XP Home Yes Yes Yes 4 GB
Windows 2000 Pro and Server Yes Yes Yes 4 GB
Windows Millennium Edition No Yes Yes 2 GB
Windows 98 and Second Edition No Yes Yes 2 GB
Windows 95 OSR2 and OSR2.5 No Yes Yes 2 GB
Windows NT4 Workstation Yes No Yes 4 GB
Windows 95 Gold (Original Release) No No Yes 2 GB
Windows NT3.5x Workstation Yes No Yes 4 GB
MS-DOS (versions 3.3 and higher) No No Yes *

* There are some exceptions, but for the most part, DOS 3.3 and higher can access up to 2 GB of single partition space. The DOS Partitioning Summary (Q69912) names some exceptions and points out that some earlier versions do not support many of current FAT16 standards.

In most cases, the maximum FAT partition that can be created and accessed by the operating systems listed above is 2 GB. 4 GB FAT partitions can be created and properly accessed only under the operating systems listed above. A dual boot NT family of operating system can create a 4 GB FAT partition and a lower-level operating system, such as Windows 98, and may be able to see data on it; however, issues will arise when data access is attempted above the 2 GB threshold that the operating system normally uses.

The maximum single file size on a FAT16 partition is 2 GB, regardless of the fact that some operating systems can have a 4 GB partition.

More information about the Maximum Partition Size Using the FAT16 File System in Windows XP, is available on Q310561 at the Microsoft PSS Web page.

Information about Accessing FAT16 Drives Larger Than 2 GB, or Maximum Partition Size Using FAT16 File System is also available on Microsoft's site.

FAT32 File Systems

FAT32 is supported by the Windows Server 2003 family of operating systems as well as a number of the newer Microsoft operating systems. FAT32 was first introduced with Microsoft Windows 95 OSR2. The major differences between FAT and FAT32 are volume and cluster sizes and that only Microsoft operating systems can natively access FAT32.

The FAT32 file system supports drives up to 2 TB in size (in theory). Because it uses space more efficiently, FAT32 uses smaller clusters (i.e., 4,096 byte clusters for drives up to 8 GB in size), resulting in more efficient use of disk space compared to large FAT16 drives.

FAT32 File System Cluster Sizes
Partition Size
Cluster Size
0 MB - less than 260 MB 512 bytes
260 MB - 8 GB 4,096 bytes
8 GB - 16 GB 8,192 bytes
16 GB - 32 GB 16,384 bytes
32 GB - 2 TB 32,768 bytes

The 50 files mentioned in the FAT16 section, all 1,024 bytes (1KB) in actual size, would consume only 409,600 bytes on a 16 GB partition formatted with FAT16, and only 204,800 bytes on a 8 GB partition. As you can see, however, we now run into the issue with FAT32 drives with 80 GB and 100 GB partitions that we did a few years ago under FAT16 -- wasted space. Those same 50 files would use 819,200 bytes on either of the two large drives previously mentioned.

While the FAT32 file system can support drives up to a standard theoretical size of 2 TB, (it "can" be jury-rigged under Windows Millennium Edition to support partitions of up to 8 TB) Windows Server 2003, Windows 2000 Server or Professional, and Windows XP Professional and Home Edition cannot FORMAT a volume larger than 32 GB using their native FAT32 file system.

The FastFAT driver can mount and support volumes larger than 32 GB that use the FAT32 file system, such as those created locally by Windows 98 or ME in dual boot configuration (subject to a variety of limitations), but you cannot CREATE one using the Format tool from within Windows Server 2003, Windows 2000 Server or Professional, or Windows XP Home or Professional. If you attempt to format a FAT32 partition larger than 32 GB, the format fails near the end of the process with the following error message: Logical Disk Manager: Volume size too big.

In summary, the advantages of the FAT32 file system are:

  • FAT32 allocates disk space much more efficiently than FAT16.
  • The root folder on a FAT32 drive is not restricted in the number of entries in the root folder as was FAT16.
  • FAT32 is a more robust file system than FAT16. FAT32 can relocate the root directory and use the backup copy of the FAT instead of the default copy. In addition, the boot record on FAT32 drives has been expanded to include a backup of critical data structures. This means that FAT32 volumes are less susceptible to a single point of failure than FAT16 volumes.

And the disadvantages are:

  • FAT32 volumes are not accessible from operating systems other than certain ones from Microsoft.
  • FAT32 partition sizes are limited to 32 GB in size using the native FAT32 file system format tools under Windows Server 2003, Windows 2000 and Windows XP.
  • No native file level security, compression or encryption available in the FAT32 file system.

Below is a list of Microsoft operating systems indicating which support native access to the FAT32 file system.

Operating System
Windows Server 2003 Yes
Windows XP Professional Yes
Windows XP Home Yes
Windows 2000 Professional Yes
Windows Millennium Edition Yes
Windows 98 and Second Edition Yes
Windows 95 OSR2 and OSR2.5 Yes
Windows NT4 Workstation No
Windows 95 Gold (Original Release) No
Windows NT3.5x Workstation No
MS-DOS (versions 3.3 and higher) No

Answers to a variety of common questions about the FAT32 File System, can be found on Q253774.

More information on the Limitations of FAT32 File System on Windows 98, ME and 2000, you can look up Q184006. You can find the information for the limitations of the FAT32 File System in Windows XP information at Q314463. Maximum partition sizes, both practical and theoretical is listed here as well.

Volumes from 33 MB to 2 TB can be accessed under Windows Server 2003; however, the maximum size that can be formatted under is 32 GB. The maximum single file size on a FAT32 partition is 4 GB, regardless of the size of the partition.

New Technology File System, is the preferred file system for all computers running Windows Server 2003. If you are running Windows NT 4.0 Service Pack 4 or later, you can read basic volumes formatted by using NTFS 5 locally on dual boot systems. Windows Server 2003, Windows 2000, and Windows XP Professional can all read NTFS partitions on both basic and dynamic volumes.

(Computers systems accessing either version of NTFS across networks are not affected. Version differences are usually considered only in local and dual boot situations.)

The following NTFS features are available under version 5:
  • File and folder permissions
  • Encryption
  • Disk quotas
  • File compression
  • Mounted drives
  • Hard links
  • Distributed link tracking
  • Sparse files
  • Multiple data streams
  • POSIX compliance
  • NTFS change journal
  • Indexing service

Detailed information on these features can be found in both the Microsoft Windows XP Professional Resource Kit Documentation and online.

If you are running Windows Server 2003 in a dual boot scenario with a system running Windows NT 4.0 Service Pack 4 or later, most of the NTFS 5 features are not available. Most read and write operations are permitted, as they do not attempt to make use of most NTFS 5 features.

Issues that may occur under this type of configuration include:

  • Windows NT4 cannot perform any operations that make use of reparse points.
  • When running Windows NT4 on a multiple-boot configuration that also runs Windows XP Professional, Windows NT4 ignores disk quotas implemented by Windows XP Professional.
  • Windows NT4 cannot perform any operations on files encrypted by Windows XP Professional.
  • Windows NT4 cannot perform any operations on sparse files.
  • Windows NT4 ignores the change journal setup under Windows XP Professional.

The NTFS file system supports drives up to 16 EB, in theory. However, because partition tables on basic disks (disks that include a master boot record) support partition sizes up to only 2 TB, dynamic volumes are a requirement when creating NTFS partitions more than 2 TB in size. Maximum volume and partition sizes start at 2 TB and range upward to almost 16 TB -- dependent on whether basic or dynamic volumes are used and whether the volume is formatted with a standard allocation unit size of 4 KB.

Windows 2000, Windows XP Professional, and Windows Server 2003 manage dynamic volumes in a special database instead of in the partition table. Therefore dynamic volumes are not subject to the 2-TB physical limit imposed by the partition table. This is why dynamic NTFS volumes can be as large as the maximum volume size supported by NTFS.

Default NTFS File System Cluster Sizes
Partition Size
7 MB to 16 MB 512 bytes
17 MB to 32 MB 512 bytes
33 MB to 64 MB 512 bytes
65 MB to 128 MB 512 bytes
129 MB to 256 MB 512 bytes
257 MB to 512 MB 512 bytes
513 MB to 1,024 MB 1,024 bytes
1,025 MB to 2 GB 2,048 bytes
2 GB to 4 GB 4,096 bytes
4 GB to 8 GB 4,096 bytes
8 GB to 16 GB 4,096 bytes
16 GB to 32 GB 4,096 bytes
32 GB to 2 TB 4,096 bytes

Advantages of NTFS are as follows:

  • NTFS uses standard transaction logging and recovery techniques. By using the log file and checkpoint information to automatically restore the consistency of the file system in the event of a failure, NTFS, for the most part, maintains the consistency of the data on the volume and the volume itself.
  • NTFS supports compression on volumes, folders, and files. Files compressed on an NTFS volume can be read and written by any Windows-based application without first being decompressed by another program. Decompression happens automatically (think of a ZIP utility on-the-fly) during the file read. The file is compressed again when it is closed or saved.
  • NTFS does not restrict the number of entries to 512 in the root folder.
  • Windows 2000 and Windows XP can format partitions up to 2 TBs.
  • NTFS manages disk space efficiently by using smaller clusters (see the Default Cluster Sizes table following the list of disadvantages).
  • The boot sector is backed up to a sector at the end of the volume.
  • You can set permissions on shares, folders, and files that specify which groups and users have access, and what level of access is permitted on NTFS partitions.
  • NTFS supports a native encryption system (EFS), to prevent unauthorized access to file contents.
  • Reparse points enable new features such as volume mount points.
  • Disk quotas can be set to limit the amount of usage allowed by end users.
  • A change journal tracks changes made to files.
  • NTFS supports distributed link tracking to maintain the integrity of shortcuts and OLE links.
  • NTFS supports sparse files so that very large files can be written to disk while requiring only a small amount of storage space.

Not surprisingly, NTFS also has disadvantages:

  • NTFS volumes are not locally accessible from MS-DOS, Windows 95, Windows 98, and Windows Millennium Edition operating systems.
  • Many advanced features of NTFS included with version 5 are not available in Windows NT.
  • On small partitions with mostly small files, the overhead of managing the NTFS file system can cause a slight performance drop in comparison to FAT.
  • Floppy disks cannot be formatted as NTFS
More detailed answers to questions about the NTFS File System, is available in the Microsoft Windows XP Professional Resource Kit Documentation.

Default Cluster Sizes for Partitions Under Windows Server 2000

Partition Size Cluster Size
7 MB-16 MB 2 KB (FAT12) Not supported 512 bytes
17 MB-32 MB 512 bytes Not supported 512 bytes
33 MB-64 MB 1 KB 512 bytes 512 bytes
65 MB-128 MB 2 KB 1 KB 512 bytes
129 MB-256 MB 4 KB 2 KB 512 bytes
257 MB-512 MB 8 KB 4 KB 512 bytes
513 MB-1,024 MB 16 KB 4 KB 1 KB
1,025 MB-2 GB 32 KB 4 KB 2 KB
2 GB-4 GB 64 KB 4 KB 4 KB
4 GB-8 GB Not supported 4 KB 4 KB
8 GB-16 GB Not supported 8 KB 4 KB
16 GB-32 GB Not supported 16 KB 4 KB
32 GB-2 TB Not supported Not supported 4 KB

Summary and Various Quick Points

  • FAT volumes smaller than 16 MB are formatted as FAT12.
  • FAT12 is used only on floppy disks and volumes smaller than 16 MB
  • FAT16 volumes larger than 2 GB are not locally accessible from computers running MS-DOS, Windows 95, Windows 98, Windows Millennium Edition and many other operating systems.
  • FAT32 volumes can theoretically be as large as 2 TB; Windows Server 2003, Windows 2000 and Windows XP limit the maximum size FAT32 volume that it can format to 32 GB. (Windows Server 2003, Windows 2000 and Windows XP Professional can read and write to larger FAT32 volumes formatted by other operating systems.)
  • NTFS volumes can theoretically be as large as 16 EB, but the practical limit is 2 TB.
  • The user can specify the cluster size when an NTFS volume is formatted. However, NTFS compression is not supported for cluster sizes larger than 4 KB.
  • Not supported means "Not supported by Microsoft." In some "chance" cases, you may be able to perform a function that is not normally supported.