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FAT-32 File System

FAT-32 is a new, updated version of the FAT (File Allocation Table) system which utilizes several features to increase performance on Wintel-based personal computers using the FAT system (as opposed to Wintel-based systems using HPFS or NTFS) with Windows 95 or Windows 98. In order to fully understand FAT-32, the informed user must first understand the basics of the FAT system.

Early FAT Systems

The first MS-DOS FAT was based upon an 8-bit system used to manage BASIC files (there was not yet an operating system for use on PC’s). This FAT was a 12-bit version first used for managing floppy disks and logical drives with a capacity of less than 16MB. MS-DOS 3.0 introduced the FAT-16 system for larger drives, and this is the file system currently in use by most Wintel-based personal computers.

What is the FAT?

FAT is a File Allocation Table that MS-DOS and Windows 9X (and non-NTFS Windows NT) use to link the clusters of a file together. The table stores information concerning the locations of the different clusters of individual files. File and directory entries point to the first cluster in the file, which the OS uses to find the first entry in the FAT. The FAT then tracks the location of the remaining clusters in the file.

Think of the logical drive as a library containing thousands of books. The FAT would be equivalent to the card catalog that indexes each book and provides information as to where each book is located.

Limitations of FAT-12 and FAT-16

The FAT-12 and FAT-16 systems are not without limitations, some of which did not become obvious until the advent of larger (greater than 2GB) fixed disks. These limitations include:

  • The Boot Sector has always been one sector at a specific location. If that sector becomes corrupted, then the system will not boot
  • The Root Directory is limited in size based on the media used, while also remaining fixed in its location.
  • The FAT-16 system is limited in size to 65,525 clusters with each cluster being fixed in a size relative to the logical drive. If both the maximum number of clusters and their maximum size (32K) is reached, then the largest supported logical drive size is 2GB.
  • Storing files in a FAT system wastes space in larger drives as the size of the cluster increases. This is known as Cluster Allocation Granularity (slack space). The space allocated for storing a file is based upon cluster size, not file size, so, a 10K file stored in a 32K cluster wastes 22K of space.

FAT-32 File System

FAT-32 goes beyond the capabilities of FAT-16, mainly through the addition of the new logical partition size and smaller cluster size.

  • FAT-32 breaks the existing FAT-16 2GB logical drive limitation by extending a single logical drive capacity to 2 Terabytes (2,047GB).
  • In FAT-16, the cluster size is inflexible and its size is based on the logical drive size (a 2GB drive must use a 32K cluster size). With FAT-32, the range for a 4K cluster size includes logical drive sizes between 512MB and 8GB.

FAT-32 Cluster Sizes

Drive Size

Default Cluster Size

Less than 260MB*

512 bytes

512MB-8GB

4K

8.1GB-16GB

8K

16.1GB-32GB

16K

Greater than 32GB

32K

Note: FDISK does not allow Fat32 on logical drives smaller than 512MB. However, third party utilities may make use of FAT32 on smaller drives.

Implementing FAT-32

FDISK-

With the introduction of FAT-32, the FDISK command changed to allow the user the choice of converting to the FAT-32 system or staying with FAT-16. In Windows 95 OSR2, the only way to convert to FAT-32 is by running FDISK and reformatting the HDD. This, of course, results in total data loss. Windows 98 includes a utility for converting to FAT-32 within the operating system (this will be discussed later). The new FDISK screen appears as follows:

Your computer has a disk larger than 512MB. This version of Windows includes support for large disks, resulting in more efficient use of disk space on large drives, and allowing disks over 2GB to be formatted as a single drive.

IMPORTANT: If you enable large disk support and create any new drives on this disk, you will not be able to access the new drive(s) using other operating systems, including some versions of Windows 95 and Windows NT, as well as earlier versions of Windows and MS-DOS. In addition, disk utilities that were not designed explicitly for the FAT-32 file system will not be able to work with this disk. If you need access to this disk with other operating systems or older disk utilities, do not enable large drive support.

Do you wish to enable large disk support (Y/N)…………..? [ Y ]

 

**** The option to enable large disk support is Yes by default****

Answering YES to large disk support enables FAT-32. Once the choice has been made to install FAT-32 support, FDISK will continue to the standard FDISK menu, where the user can select to create the partition. Each time the user creates a partition or logical drive, the following message is displayed:

Verifying drive integrity, xx% complete.

The percentage counts 0 to 100. FDISK has always verified the integrity of the drive, but this is the first version which actually displays the status count. During verification, FDISK checks the tracks where the system files and FAT will be stored.

Initially, this check verifies the number of tracks necessary to hold the system files and FAT as if the entire disk is partitioned as one primary partition. If the user creates an extended partition, it will verify the number of tracks necessary to hold the system files and FAT as if the remaining portion is partitioned as one logical drive. This repeats until the user has finished creating logical drives.

FDISK now displays this information since it has capabilities for setting up very large drives. Without the verification percentage counter, the user may think that FDISK is hanging the system and reboot.

FORMAT

The FORMAT command has been changed to accommodate the changes in FAT-32. The default cluster size for drives of capacities ranging between 512MB and 8GB is now 4K. Format will automatically implement the 4K cluster size. Currently, Dell will not be supporting cluster sizes smaller than 4K.

FORMAT used to create a FAT-32 system will display the following screen output:

FORMAT C: /S

WARNING, ALL DATA ON NON-REMOVABLE DISK

DRIVE C: WILL BE LOST!

Proceed with Format (Y/N)? Y

 

Checking existing disk format.

Formatting 1,029.97MB

Format Complete

Writing Out File Allocation Table

Complete.

Calculating free space (this may take several minutes….)

Complete.

Volume Label (11 Characters, ENTER for none.)?

1,053,945,344 bytes total disk space

310,784 bytes used by system

1,053,634,560 bytes available on disk

 

4,096 bytes in each allocation unit

257,235 allocation units available on disk

 

The bolded selections are included to prevent the user from thinking the system has stopped responding during the format.

 

 

Issues with FAT-32

 

Booting from a previous OS

If a user tries to boot from a system disk created on a non-FAT32 system, then (s)he will receive the error: "Non-DOS Partition". The user must use a startup disk from the new OS.

Windows NT (3.x-4.x)

Windows NT versions 3.x-4.x cannot access a local FAT-32 drive. If access is attempted, the system returns the following error:

The drive is not a valid partition.

What this means is that if a user has a dual boot system with NT and Windows 98 and (s)he converts the file system to FAT-32, then NT will be inaccessible. The Windows 98 file system converter displays a message explaining this.

DriveSpace 3

DriveSpace 3 is not supported on FAT32.

Disk Manager

If a user is using Ontrack Disk Manager on a system booting from a FAT32 drive, it may result in a long pause at boot and/or the drive will be set to run in compatibility mode. To overcome this, the user must upgrade to Disk Manager version 7.04 and use the /L:0 switch.

ScanDisk

Legacy versions of ScanDisk will not work on FAT-32 drives. If the user tries to run a legacy version of ScanDisk, there are two possible errors that may result:

This version of Microsoft ScanDisk will work only with MS-DOS versions 5.0 and later.

Or:

This drive was compressed by a program that is not supported by ScanDisk. As a result, ScanDisk is unable to detect and repair compression related errors.

In both cases, the only solution is to direct the user to run the version of ScanDisk included with Windows 98.

Dell support personnel have identified another possible problem with ScanDisk and FAT-32 in situations where the cluster size has been set to 1K during conversion. If the cluster size is set to 1K, then even the Windows 98 version of ScanDisk will not run because it does not have enough stack space to store the scan result information. There is currently no known work-around for this. But, neither Dell nor Microsoft will be supporting cluster sizes less than 4K.