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What is file allocation table?

FAT Definition:

FAT, short for File Allocation Table (used by hard disks, disks, Smartmedia™, Compact Flash™, Memory Stick and other),
A table that the operating system uses to locate files on a disk. Due to fragmentation, a file may be divided into many sections that are scattered around the disk. The FAT keeps track of all these pieces.
It is a file system that was created by Microsoft in 1977. FAT ( also know as FAT, FAT16, and FAT32 ) is still in use today as the preferred file system for floppy drive media and portable, high capacity storage devices like flash drives.

FAT was the primary file system used in all of Microsoft's consumer operating systems from MS-DOS to Windows ME. The New Technology File System (NTFS) is the primary file system on Microsoft's newer operating systems but FAT is still a supported option.

Below is more information on the versions of the FAT file system:

  • FAT12 - The initial version of the FAT file system, FAT12 was introduced in 1977, even before MS-DOS, and was the primary file system for Microsoft operating systems up to MS-DOS 4.0. FAT12 supports drive sizes up to 32MB.
  • FAT16 - The second implementation of FAT was FAT16, introduced in 1981. FAT16 was the primary file system for MS-DOS 4.0 up to Windows 95. FAT16 supports drive sizes up to 2GB. It was designed originally to handle files on a floppy drive, and has had minor modifications over the years so it can handle hard disks, and even file names longer than the original limitation of 8.3 characters, but it's still the lowest common denominator. The biggest advantage of FAT16 is that it is compatible across a wide variety of operating systems, including Windows 95/98/Me, OS/2, Linux, and some versions of UNIX. The biggest problem of FAT16 is that it has a fixed maximum number of clusters per partition, so as hard disks get bigger and bigger, the size of each cluster has to get larger. In a 2–GB partition, each cluster is 32 kilobytes, meaning that even the smallest file on the partition will take up 32 KB of space. FAT16 also doesn't support compression, encryption, or advanced security using access control lists.
  • FAT32 - FAT32 is the latest version of the FAT file system. It was introduced in 1996 for Windows 95 Service Pack 2 users and was the primary file system for consumer Windows versions through Windows ME. FAT32 supports drive sizes up to 8TB. FAT32 shares all of the other limitations of FAT16, and adds an important additional limitation—many operating systems that can recognize FAT16 will not work with FAT32—most notably Windows NT, but also Linux and UNIX as well. Now this isn't a problem if you're running FAT32 on a Windows XP computer and sharing your drive out to other computers on your network—they don't need to know (and generally don't really care) what your underlying file system is.

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