In computers all storage media employ the use of a file system to store, organize, manipulate and retrieve data. The DOS, Windows, OS/2, Macintosh, and UNIX-based operating systems all have file systems in which files are placed somewhere in a hierarchical (tree) structure. It sets up the root directory and subsequent directories beneath it and can be thought of as an index or database containing the physical location of every piece of data on a hard drive. The file system allows you to add new files and folders, which are added to different parts of the "file tree" on your hard disk. The file system is created when you initialize or format your hard disk.

The smallest data element in a computing system is the bit. Bits are most commonly organized as 8-bit bytes, which are then grouped into sectors. The file system is responsible for organizing these sectors into files and directories, and keeping track of which sectors belong to which file and which are not being used.

Common File Systems

Hard Discs:  FAT (FAT12, FAT16, FAT32, exFAT), NTFS, HFS and HFS+, HPFS, UFS, ext2, ext3, ext4, btrfs, ISO 9660, ODS-5, Veritas File System, VMFS, ZFS, ReiserFS and UDF.  

Compact Discs, DVDs and Blu-ray discs: ISO 9660 and Universal Disk Format (UDF).

Flash memory devices:  Flash File System.

Magnetic tapes:  Tape File System, Linear Tape File System.

Servers:  Networks File Systems