Jos F. Kirps


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I ran my own blog from November 2006 till October 2014. All posts are still online, but I don't have time to update it anymore. Enjoy!

A Short History Of The Windows FAT File System

March 19, 2008

FAT is a proprietary computer file system originally developed by Bill Gates and Marc McDonald in 1976/1977. It became the standard file system on many operating systems, including MS-DOS and Windows (up to Windows Me).

"FAT" is an abbreviation for "File Allocation Table" - it is a quite simple and commonly used file system and is thus still supported by a large number of operating systems.

The FAT file system is relatively uncomplicated, and is supported by virtually all existing operating systems for personal computers. This ubiquity makes it an ideal format for floppy disks and solid-state memory cards, and a convenient way of sharing data between disparate operating systems.

Originally the file system had been developed for managing disks in Microsoft's BASIC. In 1980 Tim Paterson incorporated FAT into the CP/M clone operating system Microsoft had just purchased from Seattle Computer Products, this OS should finally become MS-DOS. In fact FAT was the main difference between CP/M and MS-DOS when it was released, and it was definately a key to the success of the new OS.

The first FAT version (also called FAT 12) was designed as a file system for floppy diskettes and was quite limited. Directories and the hierarchial file structure were introduced with MS-DOS 2. 0 in 1983 when IBM released the PC XT with a built-in harddisk. In 1984 MS-DOS was released along with IBMs new PC AT, it featured the updated FAT 16 allowing much larger file sizes and supporting 1. 2 MB 5. 25" floppy disks. MS-DOS 3. 2 introduced extended partition in January 1986 which finally supported partitions. In 1987/1988 the 16-bit disk sector index was extended to 32 bits with MS-DOS 4. 0 and OS/2 - the entire disk I/O code was written in assembly language and had thus to be rewritten to allows this change.

One of the major drawbacks of the FAT file system was the fact that filenames were limited to 8 characters (plus a 3 character extension). Long 255 character file names were finally made possible using a trick - VFAT (or "Virtual FAT") stored the long file names as some kind of meta information visible to the user while the DOS itself still operated with 8 character filenames. VFAT was introduced with the more user friendly Windows 95 in 1995.

FAT32 was finally developed to allow larger disk sizes and was introduced with Windows 95 OSR2. But as the maximum possible size for a file on a FAT32 volume is 4GB video capture and editing applications and some other software can easily exceed this limit.

While FAT is still the normal file system for removable media (with the exception of CDs and DVDs) today, the NTFS file system that was developed for the Windows NT line is now the recommeded file system for harddisks - it is superior to FAT from the points of view of efficiency, performance, and reliability. Since Microsoft has announced the discontinuation of its MS-DOS -based consumer operating systems with Windows Me, it remains unlikely that any new versions of FAT will appear.

file system
operating system
rick said on March 19, 2008:

This is a great story about the fat filesystem. I don't know the impetus it takes to write a new filesystem. I am amazed that different operating systems didn't support more filesystems. (irix xfs, linux ext3, mac hfs,hfs+,ufs, win fat,fat32,ntfs). You'd think that interoperability would be tantamount to a programming challenge.

amar said on March 24, 2009:

you have load one ppt file

ruban said on February 1, 2014:


Sommer Barnes said on September 06, 2015:

This is a interesting story about the fat filesystem.

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