File system

filesystemfile systemsfilesystemsfile storagefile-systemflat file systemcomputer file systemvirtual filefile accessdisk file system
In computing, a file system or filesystem controls how data is stored and retrieved.wikipedia
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ISO 9660

ISOCDFS.cdfs
For example, the ISO 9660 file system is designed specifically for optical discs.
ISO 9660 is a file system for optical disc media.

Computer file

filefilescomputer files
Taking its name from the way paper-based information systems are named, each group of data is called a "file".
Typically, files are organised in a file system, which keeps track of where the files are located on disk and enables user access.

Hard disk drive

hard drivehard diskhard drives
As of 2019 hard disk drives have been key storage devices and are projected to remain so for the foreseeable future.
Typically, some of an HDD's capacity is unavailable to the user because it is used by the file system and the computer operating system, and possibly inbuilt redundancy for error correction and recovery.

Tmpfs

temporary filesystemRAM file system
In some cases, such as with tmpfs, the computer's main memory (random-access memory, RAM) is used to create a temporary file system for short-term use.
It is intended to appear as a mounted file system, but stored in volatile memory instead of a persistent storage device.

File system fragmentation

fragmentationdisk fragmentationfragmented
File system fragmentation occurs when unused space or single files are not contiguous.
In computing, file system fragmentation, sometimes called file system aging, is the tendency of a file system to lay out the contents of files non-continuously to allow in-place modification of their contents.

Hierarchical File System

HFSComputer files (Macintosh)Hierarchical File System (HFS)
The native file systems of Unix-like systems also support arbitrary directory hierarchies, as do, for example, Apple's Hierarchical File System, and its successor HFS+ in classic Mac OS, the FAT file system in MS-DOS 2.0 and later versions of MS-DOS and in Microsoft Windows, the NTFS file system in the Windows NT family of operating systems, and the ODS-2 (On-Disk Structure-2) and higher levels of the Files-11 file system in OpenVMS.
Hierarchical File System (HFS) is a proprietary file system developed by Apple Inc. for use in computer systems running Mac OS.

NTFS

alternate data streamMFTAlternate Data Streams
The native file systems of Unix-like systems also support arbitrary directory hierarchies, as do, for example, Apple's Hierarchical File System, and its successor HFS+ in classic Mac OS, the FAT file system in MS-DOS 2.0 and later versions of MS-DOS and in Microsoft Windows, the NTFS file system in the Windows NT family of operating systems, and the ODS-2 (On-Disk Structure-2) and higher levels of the Files-11 file system in OpenVMS. Additional attributes can be associated on file systems, such as NTFS, XFS, ext2, ext3, some versions of UFS, and HFS+, using extended file attributes.
NTFS (New Technology File System) is a proprietary file system developed by Microsoft.

Inode

inode numberinodesinode table
This may be implemented by associating the file name with an index in a table of contents or an inode in a Unix-like file system.
The inode (index node) is a data structure in a Unix-style file system that describes a file-system object such as a file or a directory.

Files-11

ODS-1Record Management Services
The native file systems of Unix-like systems also support arbitrary directory hierarchies, as do, for example, Apple's Hierarchical File System, and its successor HFS+ in classic Mac OS, the FAT file system in MS-DOS 2.0 and later versions of MS-DOS and in Microsoft Windows, the NTFS file system in the Windows NT family of operating systems, and the ODS-2 (On-Disk Structure-2) and higher levels of the Files-11 file system in OpenVMS.
Files-11, also known as on-disk structure, is the file system used by Digital Equipment Corporation OpenVMS operating system, and also (in a simpler form) by the older RSX-11.

Sysfs

/systhe /sys directory
Some file systems are "virtual", meaning that the supplied "files" (called virtual files) are computed on request (such as procfs and sysfs) or are merely a mapping into a different file system used as a backing store.
sysfs is a pseudo file system provided by the Linux kernel that exports information about various kernel subsystems, hardware devices, and associated device drivers from the kernel's device model to user space through virtual files.

Fragmentation (computing)

fragmentationcontiguousinternal fragmentation
This results in unused space when a file is not an exact multiple of the allocation unit, sometimes referred to as slack space.
For example, files in a file system are usually managed in units called blocks or clusters.

Block availability map

BAM
Such metadata includes information about unused regions—free space bitmap, block availability map—and information about bad sectors.
In computer file systems, a block availability map (BAM) is a data structure used to track disk blocks that are considered free (available for new data).

Ext2

e2comprext2fsfilesystem development
Additional attributes can be associated on file systems, such as NTFS, XFS, ext2, ext3, some versions of UFS, and HFS+, using extended file attributes.
The ext2 or second extended file system is a file system for the Linux kernel.

HFS Plus

HFS+HFSMac OS Extended
The native file systems of Unix-like systems also support arbitrary directory hierarchies, as do, for example, Apple's Hierarchical File System, and its successor HFS+ in classic Mac OS, the FAT file system in MS-DOS 2.0 and later versions of MS-DOS and in Microsoft Windows, the NTFS file system in the Windows NT family of operating systems, and the ODS-2 (On-Disk Structure-2) and higher levels of the Files-11 file system in OpenVMS. Additional attributes can be associated on file systems, such as NTFS, XFS, ext2, ext3, some versions of UFS, and HFS+, using extended file attributes.
HFS Plus or HFS+ is a file system developed by Apple Inc. It replaced the Hierarchical File System (HFS) as the primary file system of Apple computers with the 1998 release of Mac OS 8.1.

Unix File System

UFSFFSUFS2
Additional attributes can be associated on file systems, such as NTFS, XFS, ext2, ext3, some versions of UFS, and HFS+, using extended file attributes.
The Unix file system (UFS; also called the Berkeley Fast File System, the BSD Fast File System or FFS) is a file system supported by many Unix and Unix-like operating systems.

Comparison of file systems

file systemfile system technologyUniFS
See comparison of file systems#Metadata for details on which file systems support which kinds of metadata.
The following tables compare general and technical information for a number of file systems.

Defragmentation

defragmentdefragmenteddefragmenter
An example is the file system defragmentation utilities.
In the maintenance of file systems, defragmentation is a process that reduces the amount of fragmentation.

Hard link

hard linkshardlink
Directory utilities may also include capabilities to create additional links to a directory (hard links in Unix), to rename parent links (".."
In computing, a hard link is a directory entry that associates a name with a file on a file system.

File system permissions

read-onlypermissionsfile permissions
File systems might store the file creation time, the time it was last accessed, the time the file's metadata was changed, or the time the file was last backed up. Other information can include the file's device type (e.g. block, character, socket, subdirectory, etc.), its owner user ID and group ID, its access permissions and other file attributes (e.g. whether the file is read-only, executable, etc.). Examples include passwords stored in the metadata of the file or elsewhere and file permissions in the form of permission bits, access control lists, or capabilities.
Most file systems have methods to assign permissions or access rights to specific users and groups of users.

Ext3

3ext3grep
Additional attributes can be associated on file systems, such as NTFS, XFS, ext2, ext3, some versions of UFS, and HFS+, using extended file attributes.
It used to be the default file system for many popular Linux distributions.

Allocation group

Often such information about an allocation group is stored inside the allocation group itself.
An AG or allocation group is a subvolume in a file system which maintains its own track of free blocks and file data (and its own journal, in the case of XFS).

Free space bitmap

free-space bitmapbitmap
Such metadata includes information about unused regions—free space bitmap, block availability map—and information about bad sectors.
Free-Space Bitmaps are one method used to track allocated sectors by some file systems.

Multics

Multics project
The first file system to support arbitrary hierarchies of directories was used in the Multics operating system.
All memory in the system was part of some segment, which appeared in the file system; this included the temporary scratch memory of the process, its kernel stack, etc.

Access control list

ACLACLsaccess control lists
Examples include passwords stored in the metadata of the file or elsewhere and file permissions in the form of permission bits, access control lists, or capabilities.
An access control list (ACL), with respect to a computer file system, is a list of permissions attached to an object.

System time

DATEsystem clocktime
The time that the file was last modified may be stored as the file's timestamp.
File systems keep track of the times that files are created, modified, and/or accessed by storing timestamps in the file control block (or inode) of each file and directory.