Originally developed by IBM, the file allocation table, or FAT, served as the foundation of early MS-DOS (Microsoft Disk Operating System) software in the mid-1980s. Although it was available in a 12-bit version, the first version of FAT to really catch on with mainstream computer users was the 16-bit version known as FAT16.

The FAT file system used a very specific format that utilized four different sectors, sometimes known as regions, to form the fundamental framework of the drive or partition. But what is the purpose of these four regions? How are they used to organize and maintain your data and, more importantly, what do they mean for the data integrity of FAT-formatted drives and partitions?

Although it's commonly referred to as the boot sector or reserved sector, this is technically the first region on a FAT drive or partition. It is located on the very first region of the disc. The boot sector is commonly used to store:

• Boot loader data
• Master boot record (MBR)
• BIOS parameter block (BPB)

Considering the importance of the data it contains, it's safe to say that the boot sector is absolutely critical to the functionality of the partition. Damage to a partition or drive's boot sector could render the entire partition or drive – and all of the data contained therein --- completely inaccessible by anything but the most advanced of data recovery tools.

FAT Region
The FAT region is the next region on the FAT file system. Since it usually covers two different copies of the system's FAT, it's primarily used for error and redundancy checking. It also controls how data or disk clusters are assigned for use in the FAT file system.

Root Directory Region
While the root directory region is commonly seen in FAT12 and FAT16 configurations, it's not used at all with later versions of the FAT file system. In earlier systems, the region serves as a table of contents that stores important data containing your system's files and directories. The root directory also has a maximum size, which is generally established when the partition is created.

In FAT32-formatted systems, this table of contents doesn't have its own directory on your drive or partition. Instead, the root directory is stored within the data region of the hard drive.

Data Region
The fourth and final region on FAT-formatted partitions and drives, the data region takes up more space than all of the other regions combined. Since it contains the data for all of the files and directories within the partition or drive, including critical system files, temporary files, and personal files, it's easy to see why it uses up so much space.

Understanding Disk Regions
For the average user on a healthy system, disk regions exist seamlessly and transparently in the background of your day-to-day computing. It's the file system's way of organizing and making sense of all your data, and knowing your way around these regions is a necessity when attempting advanced data recovery in FAT-formatted drives and partitions.

You may read more about disk formatting in Wikipedia: Disk formatting.