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Understanding File System Options

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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

Whether you’re looking for a refresher on files systems or want to learn the difference between FAT file systems and NTFS file systems, this tutorial explains the ins and outs, and pros and cons of each.

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.

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