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In computer file systems, a cluster (sometimes also called allocation unit or block) is a unit of disk space allocation for files and directories.To reduce the overhead of managing on-disk data structures, the filesystem does not allocate individual disk sectors by default, but contiguous groups of sectors, called clusters.
Floppy disks and controllers had used physical sector sizes of 128, 256, 512 and 1024 bytes (e.g., PC/AX), but formats with 512 bytes per physical sector became dominant in the 1980s. [ 3 ] [ 4 ] The most common physical sector size for hard disks today is 512 bytes, but there have been hard disks with 520 bytes per sector as well for non-IBM ...
The translation of the native 4096, 4112, 4160, or 4224-byte physical format (with 0, 8, 64, or 128-byte Data Integrity Fields) to a virtual 512, 520 or 528-byte increment is transparent to the entity accessing the hard disk drive. Read and write commands are issued to Advanced Format drives in the same format as legacy drives.
These logical sectors were larger (up to 8192 bytes) than the physical sector size (still 512 bytes) on the disk. The DOS-BIOS or System BIOS would then combine multiple physical sectors into logical sectors for the file system to work with. These changes were transparent to the file system implementation in the DOS kernel.
Bytes/ sector Sectoring Capacity rpm Encoding Note Acorn: 5 1 ⁄ 4 inch Single 1 40 10 256 soft 100 kB 300 FM 80 200 kB Double 1 40 16 256 160 kB MFM 80 320 kB 2 640 kB 3 1 ⁄ 2 inch Double 2 80 16 256 640 kB 300 MFM Format L: MOS (Electron, Master Compact) 5 1024 800 kB
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).
The FAT file system is a file system used on MS-DOS and Windows 9x family of operating systems. [3] 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.
(An ATA drive can also support 28-bit or 48-bit LBA which allows up to 128 GiB or 128 PiB respectively, assuming a 512-byte sector/block size). This is a "packet" interface, because it uses a pointer to a packet of information rather than the register based calling convention of the original INT 13h interface.