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exFAT facts for kids

Kids Encyclopedia Facts
exFAT
Developer(s) Microsoft
Full name Extensible File Allocation Table
Introduced November 2006; 18 years ago (2006-11) with Windows Embedded CE 6.0
Partition IDs
  • MBR/EBR: 0x07 (same as for HPFS/NTFS)
  • BDP/GPT: EBD0A0A2-B9E5-4433-87C0-68B6B72699C7
Structures
Directory contents Table
File allocation bitmap, linked list
Bad blocks Cluster tagging
Limits
Max volume size 128 PB, 512 TB recommended
Max file size 128 PB
Max no. of files up to 2,796,202 per directory
Max filename length 255 characters
Allowed filename
characters		 all Unicode characters except U+0000 (NUL) through U+001F (US) / (slash) \ (backslash) : (colon) * (asterisk) ? (question mark) " (quote) < (less than) > (greater than) and | (pipe)
(encoding in UTF-16LE)
Features
Dates recorded Creation, last modified, last access
Date range 1980-01-01 to 2107-12-31
Date resolution 10 ms
Forks No
Attributes Read-only, hidden, system, subdirectory, archive
File system
permissions		 ACL (Windows CE 6 only)
Transparent
compression		 No
Transparent
encryption		 Yes, EFS supported in Windows 10 v1607 and Windows Server 2016 or later.
Other
Supported
operating systems

exFAT, which stands for Extensible File Allocation Table, is a special way that computers organize and store files. It was created by Microsoft in 2006. exFAT is designed to work really well with flash memory devices. These include USB flash drives and SD cards.

Before 2019, exFAT was a private technology owned by Microsoft. But on August 28, 2019, Microsoft shared how exFAT works. This made it easier for other companies to use it.

exFAT is useful when other file systems like NTFS are too complex. It's also great when you need to store files larger than 4 GB. The older FAT32 file system has this 4 GB limit.

The SD Association has chosen exFAT as the main file system for SDXC cards. These are large SD cards bigger than 32 GB.

How exFAT Was Developed

exFAT first appeared in late 2006. It was part of Windows CE 6.0, a special Windows version for small devices. Later, it was added to regular Windows computers. This happened with Windows Vista Service Pack 1 and Windows Server 2008 in February 2008. An update also brought exFAT support to Windows XP and Windows Server 2003.

Many companies that make devices use exFAT. This includes makers of embedded systems and devices that use exFAT-formatted media. The whole FAT family, including exFAT, is good for small systems. This is because it doesn't need much memory or power. It can also be easily built into a device's firmware.

Key Features of exFAT

exFAT has several important features that make it useful for modern devices. It can handle very large files and storage devices. It also helps devices work together smoothly.

Handling Large Files and Storage

exFAT can handle much larger files than FAT32. With exFAT, a single file can be up to 16 exabytes (EB). That's a huge amount of data, about 10,000,000,000,000,000,000 bytes! This is much bigger than FAT32's 4 GB limit. This means you can easily move very large files between Windows and macOS computers.

exFAT also supports very large storage drives. It can handle volumes up to 128 PB. For context, 1 PB is 1,000,000 GB. This is a big jump from FAT32's limit of 2 TB.

Better File Management

exFAT improves how files are managed on a drive.

  • More files in one place: A single folder can hold almost 2.8 million files.
  • Faster free space finding: It uses a free-space bitmap. This helps the system quickly find empty space for new files.
  • Precise timestamps: exFAT records when files are created or changed. It does this with a precision of 10 ms. This is much more accurate than FAT's 2 seconds. It also records the last time a file was accessed.
  • Time zone support: Timestamps include information about the time zone. This helps keep times accurate across different regions.

Other Important Details

  • No short file names: Unlike older FAT versions, exFAT doesn't use short 8.3 file names. It uses longer file names directly.
  • Large cluster sizes: It supports cluster sizes up to 32 MB. This helps with efficiency for large files.
  • Data protection: exFAT uses checksums to check for errors in important data. This helps keep your files safe from corruption.
  • Encryption support: In newer Windows versions, exFAT supports EFS. This allows you to encrypt your files for better security.

Windows XP needs a specific update (KB955704) to use exFAT. Windows Vista needs its Service Pack 1. Newer Windows versions like Windows 7 and 10 fully support exFAT. Windows 7 also allows using exFAT drives for ReadyBoost. This feature helps speed up your computer.

exFAT is not a journaled file system by default. This means it doesn't keep a log of changes. This can sometimes make recovery harder if a device is removed during a write. However, an optional feature called TexFAT can add more backup tables.

Because exFAT allows files larger than 4 GB, it's great for recording long HD videos. Digital cameras using FAT32 often split videos into smaller 2 GB or 4 GB parts. exFAT avoids this.

Efficiency for Flash Devices

exFAT is designed to be efficient for flash memory. It helps devices like SDXC cards achieve fast write speeds. It does this by using a separate "cluster bitmap." This bitmap quickly tracks which parts of the storage are free or used. This reduces the work needed to update the main file allocation table.

Also, a special bit in the file's record can show if a file is stored in one continuous block. If it is, the system can read it faster. This is similar to an "extent" in other file systems.

Where exFAT is Used

exFAT is supported by many different operating systems and devices.

Operating System Support

Device Adoption

exFAT is the official file system for SDXC cards. Because of this, devices that don't support exFAT cannot officially advertise themselves as SDXC compatible. This is true even if they can use SDXC cards by formatting them differently.

Many high-capacity flash drives, like USB sticks and solid-state drives (SSDs), come pre-formatted with exFAT. This helps ensure they work with many different devices.

Microsoft has made agreements with many companies to use exFAT. These include BlackBerry, Panasonic, Sony, Canon, Audiovox, LG Automotive, and BMW.

Technical Details

exFAT has some specific technical features that help it work efficiently.

Default exFAT cluster sizes in Windows
Volume
size		 Cluster
size		 Cluster
count
007 MB to <256 MB 004 KB <00065,536
256 MB to <032 GB 032 KB <01,048,576
032 GB to <512 GB 128 KB <04,194,304
512 GB to <001 TB 256 KB
001 TB to <002 TB 512 KB
002 TB to <004 TB 001 MB
004 TB to <008 TB 002 MB
008 TB to <016 TB 004 MB
016 TB to <032 TB 008 MB
032 TB to <064 TB 016 MB
064 TB to <512 TB 032 MB <16,777,216
Notes:

Finding Files Faster

exFAT uses a special method to find files quickly. It creates a "hash" (a short code) for each file name. When you search for a file, the system first compares these short hash codes. If the hashes match, it then checks the full file name. This makes searching much faster, especially in large folders.

Pre-allocating Space for Files

Like NTFS, exFAT can reserve space on a disk for a file even before it's fully written. This is called "pre-allocation." It uses two different numbers for each file: one for its actual size and another for the space it has reserved. This helps prevent old data from being accidentally seen in new files.

Protecting Data with Checksums

exFAT uses checksums to make sure important data stays correct.

  • Boot record check: The "volume boot record" (VBR) is a key part of the disk. A checksum checks if the VBR has been changed. This helps protect against viruses or corruption.
  • Upcase table check: There's a table that helps convert file names to uppercase. A checksum ensures this table hasn't been corrupted. If it were, files might not be found.
  • Directory file set check: Each file's information is stored in a "file set." A checksum covers this entire set. If the file set is changed by accident or on purpose, the checksum will show an error.

When a device with exFAT is connected, these checksums are checked. If any checks fail, the file system might not be used. This helps prevent data loss or errors.

Optimizations for Flash Storage

exFAT has features designed to work well with flash memory.

  • Alignment: It can align its internal structures with the flash memory blocks. This helps writes happen more efficiently.
  • OEM parameters: It can store information about the flash storage, like its block size.
  • Less writing: It avoids using a journal, which means less data is written to the flash memory. This can help extend the life of the flash device.

Legal Status and Open Source

For a long time, exFAT was a private technology. This meant that creating free software to use exFAT was difficult. Companies worried about being sued by Microsoft for using their patents.

However, on August 28, 2019, Microsoft changed this. They published the official details of exFAT. They also allowed members of the Open Invention Network (OIN) to use their exFAT patents. This made it much easier for Linux and other open-source systems to support exFAT.

Implementations for Linux

Before 2019, Linux users could use a FUSE-based driver called fuse-exfat. This allowed them to read and write to exFAT drives.

In 2013, Samsung Electronics released a Linux driver for exFAT. This driver was later included in the main Linux kernel starting with version 5.4 in November 2019. A newer, improved version was added in kernel 5.7. This made native exFAT support available for many Linux and Android devices.

Companies like Paragon Software Group and Tuxera also offer their own exFAT solutions. These are often used in commercial products.

See also

Kids robot.svg In Spanish: ExFAT para niños

  • Design of the FAT file system
  • List of file systems
  • Comparison of file systems
  • Memory Stick XC
  • Universal Disk Format