How Fat is the Fat – The Windows File Allocation Table

What is FAT

And just how fat is it?

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For the uninitiated, FAT means File Allocation Table. In order to understand what the File Allocation Table is all about, you must first understand some things about your hard disk, its data storage technology and structures. Rather than getting into a deep technical discussion here, we will try and provide just a basic understanding.

Essentially your hard disk is a box within which there is one or more small circular platters. Etched onto these platters is a set of concentric circles that begin at the outer edge of the platter and continue to the center. Each of these concentric circles is numbered, beginning with the number zero for the outer track and continuing to the center. Each of these tracks is broken down into segments that are referred to as sectors, with each sector being capable of storing up to 512 bytes of data. The sector is the smallest storage segment of a hard disk that is addressable by your computers file system, although it cannot be accessed directly. It must be accessed as a part of a cluster.

While it is possible to have each track defined as a single sector, doing so would be a tremendous waste of space due to the way files, or data, must be stored. Let’s say that a given hard disk track is capable of storing 5 million of bytes of data, and you had one document or file that consisted of only 2,000 bytes. A file system will only permit your single file of 2,000 bytes of data to be stored in a container capable of holding 5 million bytes. This is because file systems won’t permit the mixing of files as it cannot distinguish which byte of information belongs with another to make up a single file.

In order to grasp the advantages that the FAT 32 file system has to offer over the FAT 16 file system, it is important to understand what FAT is and how it manages your hard disk. FAT, or the file allocation table, is a database that keeps track of every file on your hard disk. Under this system, your hard disk is divided into 512-byte pieces called sectors, which are then grouped into larger pieces called clusters. As the result of early design limitations, the maximum number of clusters that the FAT 16 system can manage is 65,535, and in order to stay within this limit on larger hard disks, the FAT 16 system increases the size of the clusters accordingly. The size of the clusters depends on the overall size of the hard disk. As an example, a 512MB (megabyte) hard disk uses 8KB (kilobyte) clusters, a 850MB hard disk uses 16KB clusters, and a 1.2GB (gigabyte) hard disk uses 32KB clusters, etcetera.

As you can see from the example, once you get to a 1.2GB hard disk, the size of a cluster grows so large that the storage system becomes very inefficient, especially if you have many small files on your hard disk. No matter how small the file is, it will consume at least one cluster. For instance, if you store a 1KB file on a 1.2GB hard disk, that small file will take up an entire 32KB of space. The remaining 31KB will be empty. The empty space in a cluster is called slack space. Since the operating system can’t write data into slack space, it’s completely wasted.

Aside from the inefficiency of FAT 16 on larger drives, it has a maximum partition size of 2GB. If you were to purchase a 4GB hard disk, you would have to partition or divide it into two disks of 2GB each in order to format it with FAT 16. No, this doesn’t mean you’re going to cut your new hard disk in half. Partitioning is a procedure whereby your hard disk is divided into sections or logical disks through the use partitioning tools such as Fdisk.

Before we get too much further, if you are reviewing this in anticipation of upgrading your present operating system on your computer, now would be an excellent time to backup the data that is important to you, such as documents, email, messages and passwords. Take your time and plan your moves carefully. If you are upgrading your present operating system to Windows® 98, you may want to review our support section on the Windows® 98 operating system.

How is FAT32 more efficient?
Now that you have a basic understanding of how the FAT works and a few of the problems that are inherent in its design, you will be able to understand the advantages of the FAT 32 system better. To begin with, it’s important to stress that FAT 32 is still based on the original FAT system and works similarly in order to remain compatible with existing programs, networks, and device drivers. The biggest improvement in FAT 32 is its ability to efficiently manage storage space on today’s large hard disks. It can handle disks larger than 2GB and format them as single, un-partitioned disk with a single drive letter. This, of course, has two caveats, (1) Your motherboard and Bios must not have a limitation of hard drive size, such as some of the more recent problems that have developed where motherboards have an 8 gigabyte drive limitation, or (2) if you are using a drive size of 30 gigabytes or larger and you are using Windows® 98, you must download and install the patch offered by Microsoft. You can review more about these limitations in our segments on Drive Size Barrier and Limitations.

Smaller Cluster Size
To improve storage efficiency, the FAT 32 system uses a 4KB cluster size for all hard disks under 8GB. This reduces the amount of slack space found on your hard disk when you save small files. For example, on a 1GB hard disk using the old FAT system, a 1KB file takes up 32KB of space, as we mentioned earlier. However, a 1KB file on the same hard disk using the FAT32 system takes up only 4KB of space, a savings of 28KB. This may sound trivial, but when you’re dealing with an entire hard disk that has thousands of files, the savings is dramatic. As a matter of fact, so dramatic that Microsoft guarantees that you’ll see at least 10 to 15 percent more efficient use of disk space on the average large hard disk. In some cases, we’ve determined the space savings to be even larger, reaching the 50-percent range. Of course, your results may vary depending on the number of small files on your hard disk.

Improved Reliability
FAT32 has other advantages over its predecessor that are worth mentioning. Several of these advantages fall into the category of improved reliability. For instance, under the FAT 16 system, the root directory can be located only at the beginning of the hard disk. If anything happens to that section of the hard disk, the whole thing will be unusable. Can it be recovered? Possibly, with special disk tools and then recovery is only a maybe, a big maybe!

Under the FAT 32 system, the root directory can be located anywhere on the hard disk. This means that if anything happens to the section of the hard disk storing the root directory, the new FAT 32 hard disk utilities will be able to move the root directory to a safe location on the hard disk and repair the defective area.

Another advantage FAT 32 has over FAT 16 is that it can use both the default and the copy of the FAT. Both FAT 16 and FAT 32 maintain two copies of the actual file allocation table, the default and a backup copy. But the FAT 16 system can use only the default copy to run your system. This means that if something happens to the FAT, your system will go down. The backup copy can be used only by low level disk utilities when repairing the default FAT. However, if something happens to the default FAT on a FAT 32 system, the system will continue to run by using the backup copy until the default can be repaired.

This ability to run off either of the copies of the FAT opens the door to greater improvements in the near future. The most important of these will be the ability to dynamically resize your partitions without losing data. One of the best third party programs for moving and resizing hard drive partitions is Partition Magic®, developed by PowerQuest.

Improved Performance
In addition to the more efficient use of storage space on today’s large hard disks and its reliability enhancements, FAT 32 improves overall performance. You can expect your applications to respond at least 50 percent faster than they do when running under the FAT 16 system. Furthermore, because FAT 32 is a brand-new system from the ground up, a Windows® 98 system running FAT 32 uses fewer system resources than a Windows® 98 system running FAT 16.

A Larger Root Directory
As we mentioned, the FAT 32 system allows you to locate the root directory anywhere on a hard disk. It also eliminates the 512 entry limit of the root directory. The FAT 16 system uses 32 sectors of 512 bytes each to store the root directory. This limits the size of the root directory on a hard disk to 512 entries. In other words, you can have at most 512 files and folders in the root directory. Under the FAT 32 system, you can have as many files and folders in the root directory as you want.

Larger Hard Drives
If you thought a gigabyte hard disk was large, wait until hard disk manufacturer’s release their first terabyte (TB) hard disks. (A terabyte is equal to 1,099,511,627,776 bytes, or roughly one trillion bytes.) In preparation for that day, Microsoft has given FAT 32 the ability to support hard disks as large as 2TB, however there are limitations.

Okay, we’ve given you the positives, now here are the Pitfalls
As we mentioned, there are some pitfalls to using FAT 32 that you should be aware of before you make the decision to either setup or convert your hard disk to FAT 32.

  • If you should choose to save your existing operating system files during a Windows® 98 upgrade installation, or try restoring from a backup with the idea that you can uninstall Windows® 98 and revert to your previous operating system if you need to do so, you won’t be able to do so. If you convert to FAT 32, you won’t be able to do this unless your previous operating system was Windows® 95 OSR2 and you were already running FAT 32.
  • If you’re currently dual booting between Windows® 98 and Windows® 3.x, Windows® NT 3.x, or Windows® NT 4.0. In that case, if you convert your hard disk to FAT 32, you’ll lose the dual-boot functionality.
  • If you’re using DriveSpace or another Windows® 98 compatible disk compression package, you won’t be able to convert your system to FAT 32. However, if your hard disk is at least 512MB, you may want to abandon disk compression in favor of FAT 32 because it’s more efficient than FAT 16.
  • If your computer has a built-in sleep mode to save power when you’re not using it, converting to FAT32 may disable this feature. For more details on how this might effect your system, you may want to check with the company that manufactured your system.
  • The next thing you need to be aware of is that older versions of hard disk utilities that were designed for the FAT 16 system simply won’t work on a FAT 32 system. Of course, Windows® 98 has its own built-in utilities that are compatible with FAT 32, as are the most recent versions of Norton’s Utilities. Additionally, once you convert to FAT 32, there is no a built-in Windows® 98 utility that will allow you to convert back to FAT 16. If you decide to convert back to FAT 16 and you don’t want to purchase any additional software, you’ll need to repartition and reformat your hard disk. On the other hand, several third-party utilities, such as Partition Magic® from PowerQuest, will allow you to perform the conversion from Windows® FAT 32 back to FAT 16.
  • Finally, if you boot up your system from a MS-DOS® or regular Windows® 95 system disk, you won’t see the FAT 32 partition. This is a good reason to either make a Windows® 95 Startup boot disk from a machine already running Windows® 95 OSR2b or use a Windows® 98 startup disk during the installation procedure.

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