Fat32 Information

Quick links

About FAT32
Features
Compatibility
Performance
Creating FAT32 drives
Why not just add NTFS
Technical Implementations
FAT32 FAQ

About FAT32

The existing File Allocation Table (FAT) file system was invented in 1977 as a way to store data on floppy disks for Microsoft stand-alone Disk Basic. Although originally intended for floppy disks, FAT has since been modified to be a fast, and flexible system for managing data on both removable and fixed media. In 1996, Windows 95 OSR2 came out with FAT32, a new and improved FAT.

A new generation of very large hard disks will soon be shipping, and the existing FAT data structures have finally reached the limit of their ability to support ever larger media. FAT currently can support a single disk volume up to 2 Gigabytes in size. FAT32 is an enhancement of the FAT file system that supports larger hard drives with improved disk space efficiency.

System Requirements: Fat32 cannot be downloaded and is only available with Windows 95 OSR2 and Windows 98. To see what version of Windows you are running, see the Windows Versions page.

Features

FAT32 provides the below enhancements over previous implementations of the FAT tile system:

Supports up to 2 terabytes in size

Uses space more efficiently. FAT32 uses smaller clusters (e.g. 4kb clusters for drives up to 8GB in size), resulting in up to 5% more efficient use of disk space relative to large FAT drives. The below chart is an example of what the cluster size would be for the various sizes of hard drives as you can see a 32GB drive or larger will support the same cluster size as FAT16.

Drive Size Default Cluster Size
Less than 512MB 512 Bytes
< = 8GB 4 Kilobytes
< = 16GB 8 Kilobytes
< = 32GB 16 Kilobytes
> = 32GB 32 Kilobytes

More robust. FAT32 can relocate the root directory and use the backup copy of the FAT instead of the default copy. The boot record on FAT32 drives has also been expanded to include a backup of critical data structures so they are less susceptible to a single point of failure.

More flexible. The root directory a FAT32 drive is now an ordinary cluster chain, so it can be arbitrarily larger and located anywhere on the drive. FAT mirroring can be disabled, allowing a copy of the FAT other than the first to be active. These features allow for dynamic re-sizing of FAT32 partitions. Note, however, that while the FAT32 design allows for this compatibility, it will not be implemented by Microsoft in the initial release.

Compatibility

To maintain the greatest compatibility possible with existing applications, networks, and device drivers, FAT32 was implemented with as little change as possible to Windows 95's existing 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 add on-disk data structures and published APIs will fail on FAT32 drives. Most applications will be unaffected by these changes. Existing utilities and drivers should continue to work on FAT32 drives. However, MS-DOS block device drivers (e.g. ASPIDISK.SYS) and disk utilities for these need to be revised to support FAT32 drives.

All of Microsoft's bundled disk utilities (format, FDISK, Defrag, MS-DOS ScanDisk, Windows ScanDisk, and DriveSpace) have been revised to work with FAT32. Microsoft has worked with leading device driver and disk utility vendors to support FAT32.

Performance

For most users, FAT32 has a negligible performance impact. Some applications may see a slight performance gain from FAT32. In other applications, particularly those heavily dependent on large sequential write operations, FAT32 may result in a modest performance degradation. The overall effect on raw disk performance is less than 5% however, and the overall impact on application performance as measured by Winstone is typically less than 1%.

Creating FAT32 drives

In OEM Service release 2, if you run the FDISK utility on a large system with a drive over 512MB, it will ask whether to enable large disk support. If you answer yes, any partition you create that's greater than 5I2MB will be marked as a FAT32 partition.

Why not just add NTFS to Windows 95?

NTFS is an advanced file system, with support for many features not present in FAT32, including per-file compression, security, and transitioning. It is not feasible to implement NTFS within the memory and compatibility constraints of the Windows 95 platform. Windows 95 still supports real-mode MS-DOS for booting and running some MS-DOS based games. Adding NTFS support to the MS-DOS kernel would have required a significant amount of MS-DOS memory, and that would have precluded the use of many MS-DOS mode games and applications. Protect-mode only support for NTFS would not have allowed Windows to boot from an NTFS volume.

Technical implementation

Because of the compatibility considerations described above, the implementation of FAT32 involved very little change to Windows 95. The Major differences between FAT32 and earlier implementations of FAT are as follows:

Two new partition types are defined: OxB and OxC. Both indicate FAT32 volumes; Type OxC indicates a FAT32 partition that requires extended INTI3 support (LBA).

The boot record on FAT32 drives requires 2 sectors (due to expansion and addition of fields within the BPB). As a result, the number of reserved sectors on FAT32 drives is higher than on FATI6, typically 32. This expanded reserved area allows two complete copies of the boot record to be stored there, as well as a sector, in which free space count and other file system information is stored.

The FAT is now larger, because each entry now takes up 4 bytes and there are typically many more clusters than on FATl6 drives.

The root directory is no longer stored in a fixed location.

A pointer to the starting cluster of the root directory is stored in the extended BPB.

The on-disk format directory entries is unchanged, except that the two bytes previously reserved for Extended Attributes now contain the high order word of the starting cluster number.

MS-DOS APls that rely on intimate knowledge of the file system layout fail on FAT32 drives. For instance, GetDPB (int21 h, function 32h), Int 25/26h Absolute disk read/write, and most of the Int 21 h, function 440Dh IOCTLs will fail on FAT32 drives. New forms of these APls are provided in OEM service release 2 which work on all FAT drives.

Win32 APls are not affected by FAT32, with the exception of one additional API called GetFreeSpaceEx() for determining the true free space on a FAT32 volume.

FAT32 FAQ

Which operating systems come with Fat32?

Windows 95 OSR2, Windows 98.To determine what version of Windows you have, see the Windows Versions page.

Can I download Fat32?

We are un-aware of any location that you can download Fat32.

Can Fat32 be converted back to Fat16?

Unfortunately, it can not be converted without erasing all of the information that is on the hard drive. To remove the Fat32 and re-initialize Fat16, you must Fdisk the hard drive, delete all partitions, and recreate without using extended support (FAT32).

Does Windows NT support Fat32?

No

Additional information

  • See our FAT, file system, and NTFS definitions for further information and related links on these terms.