FAT32

FAT32

The FAT (File Allocation Table) file system originated in the late 1970s and early 1980s and was the file system supported by the MS-DOS operating system. FAT32 is a derivative of the File Allocation Table (FAT) file system that supports drives with over 2GB of storage. Because FAT32 drives can contain more than 65,526 clusters, smaller clusters are used than on large FAT16 drives. This method results in more efficient space allocation on the FAT32 drive. The largest possible file for a FAT32 drive is 4GB minus 2 bytes. The FAT32 file system includes four bytes per cluster within the file allocation table. Note that the high 4 bits of the 32-bit values in the FAT32 file allocation table are reserved and are not part of the cluster number.

Disk Structure

The basic FAT32 file system is characterized as file allocation table (FAT), which

is really a table that resides at the very “top” of the volume. A section of disk at the

beginning of each partition is set aside to contain the table. The table has one entry for

each disk block, and is indexed by block numbers. The FAT is used much as a linked list.

The directory entry contains the block number of the first block of the file. The table

entry indexed by that block number then contains the block number of the next block in

the file. The chain continues until the last block, which has a special end-of-file value as

entry.

FAT Naming convention

FAT uses the traditional 8.3 file naming convention and all filenames must be

created with the ASCII character set. The name of a file or directory can be up to eight

characters long, then a period (.) separator, and up to a three-character extension. The

name must start with either a letter or number and can contain any characters except

for the following:

. " / \ [ ] : ; | = ,

If any of the above characters are used, unexpected results may occur. The name

cannot contain any spaces.

The following names are reserved:

CON, AUX, COM1, COM2, COM3, COM4, LPT1, LPT2, LPT3, PRN, NUL

Both FAT16 and FAT32 have the capability of VFAT. VFAT is a technical term for a

long file name. VFAT allows up to 255 characters for a file name instead of the 8.3 file

name as discussed.

Advantages of FAT32

FAT32 provides the following enhancements over previous implementations of

the FAT file system:

It supports up to 2 Terabytes in size.

Uses space more effectively - FAT 32 uses smaller clusters (e.g. 4kb clusters for

drives up to 8GB in size), resulting in 10 to 15% more efficient use of disk space

relative to large FAT drives.

It is more robust and is more flexible - the root directory on a FAT32 drive is now

an ordinary cluster chain, so it can be arbitrarily large and located anywhere on

the drive. In addition, FAT mirroring can be disabled, allowing a copy of the FAT

other than the first one to be active. These features allow for dynamic resizing of

FAT32 partitions.

Disadvantages of FAT32

Despite its popularity, the FAT32 File System is not a perfect file system. It

suffers from three major problems:

Fragmentation.

Storage efficiency - The storage efficiency of the FAT32 File System degrades

for larger partitions.

It is not fault tolerant - The FAT32 File System is a corruptible file system where

a computer crash, a hardware malfunction, or a programming glitch can destroy

the file system.