Microsoft KB Archive/154997

= Description of the FAT32 File System =

Article ID: 154997

Article Last Modified on 1/19/2007

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APPLIES TO


 * Microsoft Windows Millennium Edition
 * Microsoft Windows 98 Second Edition
 * Microsoft Windows 98 Standard Edition
 * Microsoft Windows 95
 * Microsoft Windows 95
 * Microsoft Windows 95

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This article was previously published under Q154997



NOTE: This article is for informational use only. It does not contain any troubleshooting information. If you are searching for troubleshooting information that is not mentioned in this article, search the Microsoft Knowledge Base again by using keywords that are listed in the following Microsoft Knowledge Base article:

242450 How to Query the Microsoft Knowledge Base Using Keywords



SUMMARY
This article describes the FAT32 file system that is included with Windows 95 OEM Service Release 2 (OSR2), Windows 98, and Windows Millennium Edition (Me).



MORE INFORMATION
Windows 95 OSR2, Windows 98, and Windows Me include an updated version of the FAT file system. This updated version is called FAT32. The FAT32 file system allows for a default cluster size as small as 4 KB, and includes support for EIDE hard disk sizes larger than 2 gigabytes (GB).

NOTE: Microsoft Windows NT 4.0 does not support the FAT32 file system. For additional information about supported file systems in Windows NT 4.0, click the article number below to view the article in the Microsoft Knowledge Base:

100108 Overview of FAT, HPFS, and NTFS File Systems

FAT32 Features
FAT32 provides the following enhancements over previous implementations of the FAT file system:
 * FAT32 supports drives up to 2 terabytes in size.

NOTE: Microsoft Windows 2000 only supports FAT32 partitions up to a size of 32 GB.
 * FAT32 uses space more efficiently. FAT32 uses smaller clusters (that is, 4-KB clusters for drives up to 8 GB in size), resulting in 10 to 15 percent more efficient use of disk space relative to large FAT or FAT16 drives.
 * FAT32 is more robust. FAT32 can relocate the root folder and use the backup copy of the file allocation table instead of the default copy. In addition, the boot record on FAT32 drives is expanded to include a backup copy of critical data structures. Therefore, FAT32 drives are less susceptible to a single point of failure than existing FAT16 drives.
 * FAT32 is more flexible. The root folder on a FAT32 drive is an ordinary cluster chain, so it can be located anywhere on the drive. The previous limitations on the number of root folder entries no longer exist. In addition, file allocation table mirroring can be disabled, allowing a copy of the file allocation table other than the first one to be active. These features allow for dynamic resizing of FAT32 partitions. Note, however, that although the FAT32 design allows for this capability, it will not be implemented by Microsoft in the initial release.

FAT32 Compatibility Considerations
To maintain the greatest compatibility possible with existing programs, networks, and device drivers, FAT32 was implemented with as little change as possible to the existing Windows architecture, internal data structures, Application Programming Interfaces (APIs), and on-disk format. However, because 4 bytes are now required to store cluster values, many internal and on-disk data structures and published APIs have been revised or expanded. In some cases, existing APIs will not work on FAT32 drives. Most programs will be unaffected by these changes. Existing tools and drivers should continue to work on FAT32 drives. However, MS-DOS block device drivers (for example, Aspidisk.sys) and disk tools will need to be revised to support FAT32 drives.

All of the Microsoft bundled disk tools (Format, Fdisk, Defrag, and MS-DOS- based and Windows-based ScanDisk) have been revised to work with FAT32. In addition, Microsoft is working with leading device driver and disk tool manufacturers to support them in revising their products to support FAT32.

NOTE: A FAT32 volume cannot be compressed by using Microsoft DriveSpace or DriveSpace 3.

FAT32 Performance
Converting to the FAT32 file system is one of the biggest performance enhancements you can make to your Windows 98-based computer.

Dual-Boot Computers
At this time, Windows 95 OSR2, Windows 98, Windows 2000, and Windows Me are the only Microsoft operating systems that can access FAT32 volumes. MS-DOS, the original version of Windows 95, and Windows NT 4.0 do not recognize FAT32 partitions, and are unable to boot from a FAT32 volume. Also, FAT32 volumes cannot be accessed properly if the computer is started by using another operating system (for example, a Windows 95 or MS-DOS boot disk).

Windows 95 OSR2 and Windows 98 can be started in Real mode (for example, to run a game) and can use FAT32 volumes.

Creating FAT32 Drives
In Windows 95 OSR2, Windows 98, and Windows Me, if you run the Fdisk tool on a hard disk that is over 512 megabytes (MB) in size, Fdisk prompts you whether or not to enable large disk support. If you answer "Yes" (enabling large disk support), any partition you create that is larger than 512 MB is marked as a FAT32 partition.

Windows 98 and Windows Me also includes a FAT32 conversion tool that you can use to convert an existing drive to the FAT32 file system. To use the conversion tool, follow these steps:
 * 1) Click Start, point to Programs, point to Accessories, point to System Tools, and then click Drive Converter (FAT32).
 * 2) Click Next.
 * 3) Click the drive that you want to convert to the FAT32 file system, and then click Next.
 * 4) Follow the instructions on the screen.

Support Boundaries
Microsoft will support the functionality of the FAT32 file system for error-free reading, and saving of files either in Real mode or Protect mode. Microsoft supports the Real-mode and Protected-mode tools that are included with Windows 95.

For legacy (older) programs that cannot be installed on a FAT32 volume, or do not properly save files or read them, you must contact the manufacturer of the software package.

NOTE: Although the FAT32 file system supports hard disks up to 2 terabytes in size, some hard disks may not be able to contain bootable partitions that are larger than 7.8 GB because of limitations in your computer's basic input/output system (BIOS) INT13 interface. Please contact your hardware manufacturer to determine if your computer's BIOS supports the updated INT13 extensions. For additional information about FAT32, click the article number below to view the article in the Microsoft Knowledge Base:

253774 Common Questions About the FAT32 File System

Keywords: kbinfo dtssb kbfaq KB154997

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