Microsoft KB Archive/310525

= Description of the FAT32 File System in Windows XP =

Article ID: 310525

Article Last Modified on 1/14/2004

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APPLIES TO


 * Microsoft Windows XP Home Edition
 * Microsoft Windows XP Professional Edition

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This article was previously published under Q310525





SUMMARY
This article describes the FAT32 file system that is included with Microsoft Windows XP.



MORE INFORMATION
Windows XP includes 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 the following:  Microsoft Windows 2000, Windows Millennium Edition, Windows 98, and Windows 95 OSR2 also support the FAT32 file system. 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 following article number 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.
 * FAT32 uses space more efficiently. FAT32 uses smaller clusters (that is, 4-KB clusters for drives up to 8 GB in size), resulting in a 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.

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 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.

Dual-Boot Computers
Windows XP, Windows 2000, Windows Me, Windows 98, and Windows 95 OSR2 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).

Creating FAT32 Volumes
The Disk Management snap-in in Windows XP is a tool for managing your hard disks and the volumes or partitions that they contain. Use Disk Management to create new FAT32 volumes, or format an existing volume to use the FAT32 file system. You can format basic and dynamic volumes to use FAT32.

Create a FAT32 Partition or Logical Drive
To create a new FAT32 partition or logical drive in Windows XP, follow these steps:
 * 1) Log on as Administrator or as a member of the Administrators group.
 * 2) Click Start, then right-click My Computer, and then click Manage.
 * 3) In the console tree, click Disk Management.
 * 4) In the Disk Management window, do one of the following:
 * 5) * To create a new partition, right-click unallocated space on the basic disk where you want to create the partition, and then click New Partition.

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 * 1) * To create a new logical drive in an extended partition, right-click free space on an extended partition where you want to create the logical drive, and then click New Logical Drive.
 * 2) In the New Partition Wizard, click Next.
 * 3) Click the type of partition that you want to create (Primary partition, Extended partition, or Logical drive), and then click Next.
 * 4) Specify the size of the partition in the Partition size in MB box, and then click Next.
 * 5) Assign a drive letter or drive path to your new partition or logical drive, and then click Next.
 * 6) Click Format this partition with the following settings, and then do the following:
 * 7) * Click FAT32 in the File system box.
 * 8) * Type a name for the volume in the Volume label box.

If you want, you can also change the disk allocation unit size, or specify whether you want to perform a quick format.
 * 1) Click Next.
 * 2) Confirm that the options that you selected are correct, and then click Finish.

The new partition or logical drive is created and appears in the appropriate basic disk in the Disk Management window.

Format an Existing Volume to Use FAT32
To format a volume, follow these steps:  Click Start, then right-click My Computer, and then click Manage. In the console tree, click Disk Management. In the Disk Management window, right-click the volume that you want to format (or reformat), and then click Format.</li> In the Format dialog box, do the following:  Click FAT32 in the File system box.</li> Type a name for the volume in the Volume label box.

If you want, you can also change the disk allocation unit size, or specify whether you want to perform a quick format.</li></ul>

Click OK.

</li> Click OK when you are prompted to format the volume.</li></ol>

The format process starts.

Support Boundaries
For legacy (older) programs that cannot be installed on a FAT32 volume, or do not properly save files or read them, contact program manufacturer.

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.

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