What is FAT (File Allocation Table)?

FAT (File Allocation Table) is part of the DOS and OS/2 file system that tracks the location of the data stored on the hard drive.

What is FAT (File Allocation Table)?

The FAT (FAT12/FAT16/FAT32/exFAT) File System

When the disk is formatted at a high level, FAT is registered twice and contains a table with an entry for each cluster on the hard disk. Each FAT entry has a 16 or 32-bit extension.

The directory list containing the filename, extension, date shows the FAT entry where the file started.

If a file is larger than a set, the first FAT entry shows the next FAT entry where the second set of the file is stored so that it continues until the end of the file.

If a cluster is corrupt, the FAT entry is marked as such, and this cluster is not reused.


FAT was created by Bill Gates and Marc McDonald in 1977 to process records at BASIC.

The Intel 8086 architecture was first included in the QDOS operating system by Tim Paterson in August 1980 for S-100 computers. This file system was the main difference between QDOS and CP/M.



The floppy file system does not support folder placement. Since the block addresses contain only 12 bits, it makes the application difficult.

The size of the disk is stored as a 16-bit account, which is expressed in sectors and limits the manageable space to 32 MB.


The FAT32 system has completely replaced the old FAT16 file system. This new version allows the creation of volumes up to 2TB compared to the 2GB limited by FAT16.

These last system clusters wasted. So if the system had to save 2 KB of files, for example, 32KB wasted by doing the entire cluster.

With the FAT32 system, you use a 4 KB cluster that saves system resources. In addition, a slight increase in the capacity of the hard disk is achieved.

The FAT16 file system has no local security for the file system or compression features, and the boot sector is not supported.

The root folder can only contain a maximum of 512 entries, so files with long names can greatly reduce the number of available entries. FAT16 does not work well with large volume sizes.


It first appeared on Windows 95 OSR2. Reformatting was required to use the benefits of FAT32.

Windows 98 included a tool to convert FAT16 to FAT32 without data loss. This support was not available in the business line until Windows 2000.

The maximum file size in FAT32 is 4 GB, which is troublesome for video capture and editing applications because the files they create easily exceed this limit.


Windows 3.11 introduced a new file system access scheme using 32-bit protected mode, bypassing the MS-DOS kernel.

To do this, he used the hardware of the BIOS or disk drive directly. This also allowed access to the cache to speed up access. All this was called VFAT or virtual FAT.

Windows NT 3.1 took the same approach but called it FASTFAT.

However, it was natural for Windows NT drivers to use 32-bit protected mode.

It is often confused with LFN (Long File Names) support because it is enabled by default in Windows 95.


exFAT was introduced in 2006 and introduced in Windows XP and Vista. As the name implies, it relates to the FAT file system and is an evolution trying to eliminate certain limitations FAT32 offers, although it does not introduce many improvements available in NTFS.

The main advantage of ExFAT compared to its predecessor is that it eliminates storage limitations, can create larger partitions, and offers more than 4GB of file storage without losing speed and writing, one of the outstanding features of FAT.

At the compatibility level, Windows and OS X have full compatibility with exFAT, things vary by NTFS, but Linux is more limited, needs specific software to be installed and offers incomplete support because it can read and write the most, but does not allow creating partitions.

Like FAT32, exFAT is ideal for use on flash drives and external drives.

FAT32 is always good as it offers more and better compatibility with a wider range of systems, so exFAT can be applied in very special cases.

FAT File Structure

The FAT file system consists of four parts:

   1) Root Directory

It is the main directory of folders and files.

   2) Boot Sector

It is always the first partition (volume) of the partition and includes basic information, pointers to other partitions, and the address of the operating system boot routine.

   3) FAT Zone

It contains two copies of the file allocation table.

These are maps of the section that shows which clusters are occupied by the files.

   4) Data Zone

This is where the contents of files and folders are stored.

Therefore, it covers almost the entire section. The size of any file or folder can be expanded as long as there is enough free set.

Each cluster is connected to the next one with a pointer. If a particular cluster is not completely full, it will waste the remaining space.


Maximum file size
32 MB
2 GB
4 GB
16 EB
Maximum number of files
Nearly Unlimited
Maximum filename length
260 with LFN
80 without LFN
260 with LFN
80 without LFN
260 with LFN
80 without LFN
260 with LFN
80 without LFN
Maximum volume size
2 MB
2 GB
2 TB
128 PB

Differences Between FAT32 and NTFS

FAT32 is also slightly slower than NTFS, the most widely used file system on Windows devices.

Using FAT32 can sometimes work best when compatibility between various devices and operating systems is desired.

However, if you want speed, FAT32 is not the best option you can choose. Therefore, NTFS is particularly high in reading speeds compared to the old FAT32 file system and is better on solid-state drives.

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