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The PC XT was the first PC with an IBM-supplied hard drive, and PC DOS 2.0 supported that hard drive with FAT12 (FAT ID 0xF8). The fixed assumption of 8 sectors per clusters on hard disks practically limited the maximum partition size to 16 MB for 512 byte sectors and 4 KB clusters.
Cluster sizes vary depending on the type of FAT file system being used and the size of the drive; typical cluster sizes range from 2 to 32 KiB. [39] Each file may occupy one or more clusters depending on its size. Thus, a file is represented by a chain of clusters (referred to as a singly linked list).
No limit defined [cf] 64 MiB (67.10 MB) 2 GiB (2.147 GB) ? ZFS: 1023 bytes Any Unicode except NUL No limit defined [cf] 16 EiB (18.44 EB) 281,474,976,710,656 YiB (2 128 bytes) 2 128: File system Maximum filename length Allowable characters in directory entries [cc] Maximum pathname length Maximum file size Maximum volume size [cd] Max number of ...
Because APM allows 32 bits worth of logical blocks, the historical size of an APM formatted disk using small blocks [3] is limited to 2 TiB. [ 4 ] The Apple Partition Map maps out all space used (including the map) and unused (free space) on disk, unlike the minimal x86 master boot record that only accounts for used non-map partitions.
The FAT12 and FAT16 file systems had a limit on the number of entries in the root directory of the file system and had restrictions on the maximum size of FAT-formatted disks or partitions. FAT32 addresses the limitations in FAT12 and FAT16, except for the file size limit of close to 4 GB, but it remains limited compared to NTFS.
If the actual size of the disk exceeds the maximum partition size representable using the legacy 32-bit LBA entries in the MBR partition table, the recorded size of this partition is clipped at the maximum, thereby ignoring the rest of the disk. This amounts to a maximum reported size of 2 TiB, assuming a disk with 512 bytes per sector (see 512e).
For example, the FAT32 file system does not support files larger than 4 GiB−1 (with older applications even only 2 GiB−1); the variant FAT32+ does support larger files (up to 256 GiB−1), but (so far) is only supported in some versions of DR-DOS, [2] [3] so users of Microsoft Windows have to use NTFS or exFAT instead.
Additionally, the limit of 65,535 allocation blocks resulted in files having a "minimum" size equivalent 1/65,535th the size of the disk. Thus, any given volume, no matter its size, could only store a maximum of 65,535 files. Moreover, any file would be allocated more space than it actually needed, up to the allocation block size.