File systems (FAT, FAT8, FAT16, FAT32 and NTFS) explained

The precise manner in which data is organised on a hard disk drive is determined by the file system used. File systems are generally operating system dependent. However, since it is the most widely used PC operating system, most other operating systems’ file systems are at least read-compatible with Microsoft Windows. The FAT file system was first introduced in the days of MS-DOS way back in 1981. The purpose of the File Allocation Table is to provide the mapping between clusters – the basic unit of logical storage on a disk at the operating system level – and the physical location of data in terms of cylinders, tracks and sectors – the form of addressing used by the drive’s hardware controller. The FAT contains an entry for every file stored on the volume that contains the address of the file’s starting cluster. Each cluster contains a pointer to the next cluster in the file, or an end-of-file indicator at (0xFFFF), which indicates that this cluster is the end of the file. The diagram shows three files: File1.txt uses three clusters, File2.txt is a fragmented file that requires three clusters and File3.txt fits in one cluster. In each case, the file allocation table entry points to the first cluster of the file. The first incarnation of FAT was known as FAT12, which supported a maximum partition size of 8MB. This was superseded in 1984 by FAT16, which increased the maximum partition size to 2GB. FAT16 has undergone a number of minor modifications over the years, for example, enabling it to handle file names longer than the original limitation of 8.3...

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