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exFAT file system (Extended File Allocation Table)

June 19th, 2010

exFAT File System exFAT (Extended File Allocation Table) is a file system designed and patentend by Microsoft and released in all versions of Windows, starting with Windows Server 2008. In addition Microsoft has released an update for Windows XP and Windows Server 2003, to add support for exFAT formatted drives.

exFAT is considered the successor to the FAT16 and FAT32 file systems. exFAT has a number of advantages and disadvantages over NTFS and FAT32. It has a theoretical maximum disk size up to 64 ZB (Zettabytes) or 64 billion terabytes, versus a 32 GB maximum under a FAT32 partition. It also allows for up to 2,796,202 files per directory, increased from 65,536 under FAT32. Finally exFAT supports Sector sizes between 512 and 4k, and a cluster size of 32 MiB (mebibyte, large megabyte).

Advantages:

  • Scalability to large disk sizes: 64 ZiB theoretical max, 512 TiB recommended max, raised from the 2 TiB limit of FAT32 partitions. Note that the built-in Windows XP format utility limits new FAT32 partitions to 32 GiB.
  • Sector size between 29 (512) and 212 (4,096) bytes.
  • Cluster size up to 32 MiB.
  • File size limit of 64 ZiB (512 TiB recommended max), raised from close to 4 GiB in FAT32.
  • 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 TFAT, a transactional file system standard (optionally WinCE activated function)
  • Provision for OEM-definable parameters to customize the file system for specific device characteristics
  • Support for UTC timestamps (starting with Vista SP2)
  • Timestamp granularity of 10 ms (better than previous FAT versions’ 2 s, but worse than NTFS’s 100 ns)

Disadvantages:

  • Windows XP and Windows Server 2003 users must have Service Pack 2 or later and install an update to support exFAT
  • Windows Vista must be Service Pack 1 or later for exFAT support
  • Devices formatted using exFAT cannot be read by any version of Windows prior to Windows XP or by any version of DOS or OS/2 (unless emulated as otherwise).
  • Devices using exFAT are unable to use Windows Vista’s ReadyBoost capability (Windows 7 adds support for ReadyBoost on exFAT formatted drives and enables a larger ReadyBoost cache due to the removal of the 4GB file size limit of FAT32)
  • Microsoft has not released the official exFAT file specification, and a license 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 and Memory Stick XC requiring exFAT)
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