FAT32

12/19/97

FAT32 is a file system developed by Microsoft to replace the FAT16 system used by MSDOS versions up to Release 6.22 and in Windows95. FAT32 was released in 1997 as package called Windows95 OSR2 installed by certain computer vendors. It will be available for general use in Windows 98 and Windows NT release 5.0.

FAT file systems store disk data in chunks called clusters. Much of the information in the FAT16 article also applies to FAT32. FAT16 limited file cluster pointers to 16 bits which limited the file system to 65535 clusters. FAT32 uses 28 bit file pointers which mean that there can be many more file pointers, or that smaller cluster sizes can be used, or both. The maximum size of a FAT32 disk is documented as 2 Terabytes using 8K or larger clusters and 1 Terabyte using 4K clusters. However, that would result in FAT Tables too large for practical mid 1990 PCs. Microsoft's compromise between FAT size and Cluster size uses the following values

Disk SizeCluster SizeFAT Size
Up to 8Gb4096Up to 2mb
8Gb-16Gb81921mb to 2mb
16Gb-32Gb163841mb to 2mb
32Gb-64Gb327681mb to 2mb
Above 64GbUnknownUnknown

FAT32 is claimed to be a few percent slower than FAT16 for file systems of the same size with similar cluster sizes. Since FAT32 will typically use either more or smaller clusters or both, it can be expected to be slightly slower than FAT16. Defragmentation of drives after conversion to FAT32 is strongly recommended. Smaller clusters should lead to less slack space and more efficient disk utilization on all but the largest disks.

FAT32 is alleged to be marginally more robust than FAT16. Other minor improvements have been made. For example the 512 file limit in the root directory has been removed. Future releases of FAT32 may include dynamic partition resizing.

FAT32 is not compatible with old disk utilities and may fail with some programs that attempt to directly access the disk. It can not easily be used on small drives (below 512mb). The commands to manually control cluster sizes and apply FAT32 to small drives are poorly documented or undocumented. It is reported that new compressed FAT16 drives can not be built if there is a FAT32 drive on the system. A BIOS update may be required to allow extended INT13 calls in order to use disk partitions larger than 8GB. Windows 95/NT4.0 with FAT32 capability do not allow dual booting of old versions of MSDOS since they could not access the FAT32 partition if one is present. Most Applications other than disk utilities will work with FAT32, but a few such as ACT! and Goldmine are known to require updates as do some programs compiled with the Borland C++ compiler.

last update 990430

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