exFAT (Extended File Allocation Table) is a proprietary file system suited especially for flash drives, introduced by Microsoft for embedded devices in Windows Embedded CE 6.0 and in their desktop operating system, Windows Vista Service Pack 1.
exFAT can be used where the NTFS file system is not a feasible solution, due to data structure overhead, or where the file size or directory restrictions of the FAT file system are unacceptable. Windows XP users can add support for exFAT by installing an update from Microsoft.
An experimental Linux kernel module that supports the reading of exFAT files is currently under development.
The advantages over previous File Allocation Table (FAT) file system versions include:
- scalability to large disk sizes
- file size limit of 264 bytes (16 EiB) [but see contradictory Microsoft article], raised from 232 bytes (4 GiB) in FAT32
- cluster size of up to 2255 sectors, implementation limit of 32 MiB
- free space allocation and delete performance improved due to introduction of a free space bitmap
- support for up to 2,796,202 files per directory, increased from 65,536
- support for access control lists (not supported yet in Windows Vista SP1)
- support for Transaction-Safe FAT File System (TFAT) (optionally WinCE activated function)
- provision for OEM-definable parameters to customize the file system for specific device characteristics
- timestamps can be in UTC rather than only local time (starting with Vista SP2)
- timestamps have a granularity of 10 ms (compared with 2 s in previous FAT versions but 100 ns in NTFS).
The disadvantages compared to previous FAT versions include:
- devices formatted using exFAT cannot be read by Windows Me, Windows 2000, and Windows Server 2003 or earlier, and other non-Microsoft operating systems
- 32-bit Windows XP requires an update to be applied in order to support exFAT
- 64-bit Windows XP does not offer exFAT support
- devices using exFAT are unable to use Windows Vista's ReadyBoost capability (but Windows 7 does support the new exFAT file system with ReadyBoost and also enables a bigger ReadyBoost cache due to the bigger space limit with exFAT)
- Microsoft has not released the official exFAT file specification, and a licence from Microsoft is required in order to make and distribute exFAT implementations
- limited or no support outside PC environment at present — most current consumer electronics, such as televisions and A/V receivers, can only handle previous FAT versions (this may change with the new SDXC cards requiring exFAT).