Design of the FAT file system
computer file system architecture design
The FAT file system is a file system used on MS-DOS and Windows 9x family of operating systems. It continues to be used on mobile devices and embedded systems, and thus is a well-suited file system for data exchange between computers and devices of almost any type and age from 1981 through to the present.
Structure
A FAT file system is composed of four regions:
FAT uses little-endian format for all entries in the header (except for, where explicitly mentioned, some entries on Atari ST boot sectors) and the FAT(s). It is possible to allocate more FAT sectors than necessary for the number of clusters. The end of the last sector of each FAT copy can be unused if there are no corresponding clusters. The total number of sectors (as noted in the boot record) can be larger than the number of sectors used by data (clusters × sectors per cluster), FATs (number of FATs × sectors per FAT), the root directory (n/a for FAT32), and hidden sectors including the boot sector: this would result in unused sectors at the end of the volume. If a partition contains more sectors than the total number of sectors occupied by the file system it would also result in unused sectors, at the end of the partition, after the volume.
Reserved sectors area
Boot Sector
On non-partitioned storage devices, such as floppy disks, the Boot Sector (VBR) is the first sector (logical sector 0 with physical CHS address 0/0/1 or LBA address 0). For partitioned storage devices such as hard disks, the Boot Sector is the first sector of a partition, as specified in the partition table of the device.
BIOS Parameter Block
DOS 3.0 BPB:
The following extensions were documented since DOS 3.0, however, they were already supported by some issues of DOS 2.11.
This brief starts where responsible research should: with the source description of “Design of the FAT file system” as computer file system architecture design. Everything that follows is an evidence route, not borrowed authority.
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The subject matters to the places & architecture register because the source frames it as computer file system architecture design. Its deeper value depends on whether names, dates, institutions and citations support that framing.
Place names and jurisdictional language are key evidence: both can reveal earlier catalogue descriptions and overlooked record series. The source revision retrieved here is dated Jul 23, 2026. The linked authority identifier is Q5424505. None of the 0 selected statements returned an explicit reference. The first chronological checks are 1981.
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This entry incorporates text from “Design of the FAT file system” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.