An extent is a contiguous area of storage in a computer file system, reserved for a file. When starting to write to a file, a whole extent is allocated. When writing to the file again, possibly after doing other write operations, the data continues where the previous write left off. This reduces or eliminates file fragmentation. In computing, a file system (often also written as filesystem) is a method for storing and organizing computer files and the data they contain to make it easy to find and access them. ... In computer storage, there are three related uses of the term fragmentation: external fragmentation, internal fragmentation, and data fragmentation, all related to storage. ...

Extents are supported in:

• Macintosh Hierarchical File System and HFS Plus
• SGI XFS (Designed to be an extent based file system)
• Reiser4 (in "extents" mode)
• NTFS (via the preallocation API, namely SetEndOfFile and SetFileValidData functions)
• Universal Disk Format (UDF)
• VERITAS File System (via the preallocation API and CLI).
• Linux ext4 - (when enabled)
• OS/2 and eComStation HPFS
• JFS for AIX, OS/2/eComStation and Linux
• BFS for BeOS, Zeta and Haiku
• The SINTRAN III file system

The CP/M file system uses extents as well, but those don't correspond to the definition given above. CP/M's extents are contiguous only in the sense that they appear as a single block in the combined directory/allocation table; they are not necessarily contiguous on the data area of the disk. Hierarchical File System (HFS), is a file system developed by Apple Computer for use on computers running Mac OS. Originally designed for use on floppy and hard disks, it can also be found on read-only media such as CD-ROMs. ... HFS Plus or HFS+ is a file system developed by Apple Computer to replace their Hierarchical File System (HFS) as the primary file system used on Macintosh computers. ... XFS is a high-performance journaling file system created by Silicon Graphics for their IRIX operating system. ... Reiser4 is a computer file system, a new from scratch successor to the ReiserFS file system, developed by Namesys and sponsored by DARPA as well as Linspire. ... NTFS is the standard file system of Windows NT and its descendants Windows 2000, Windows XP, Windows Server 2003, and Windows Vista. ... The Universal Disk Format (UDF) is a format specification of a file system for storing files on optical media. ... The VERITAS File System, or VxFS, is an extent-based file system that was the first commercial journaling file system, and was developed by VERITAS Software. ... Linux (IPA pronunciation: ) is a Unix-like computer operating system. ... The ext4, or fourth extended filesystem is a journalled file system that was revealed on October 10, 2006 by Andrew Morton as a compatible improvement to the ext3, featuring support for volumes up to 1024 petabytes and added extent (allocation of an area for a file to use) support. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... eComStation is a PC operating system based on OS/2, published by Serenity Systems International, USA. It includes several additions and accompanying software. ... HPFS or High Performance File System, is a file system created specifically for the OS/2 operating system to improve upon the limitations of the FAT file system. ... JFS is a journaling filesystem created by IBM. It is available under an open source license. ... AIX (Advanced Interactive eXecutive) is a proprietary operating system developed by IBM based on UNIX System V. Before the product was ever marketed, the acronym AIX originally stood for Advanced IBM UNIX. The scalable AIX 5L 5. ... The Be File System (BFS, occasionally misnamed as BeFS) is the native file system for the BeOS operating system. ... BeOS is an operating system for personal computers which began development by Be Inc. ... The correct title of this article is . ... The tone or style of this article or section may not be appropriate for Wikipedia. ... SINTRAN III was a real-time, multitasking, multi-user operating system used with Norsk Data computers from 1974. ... CP/M was an operating system originally created for Intel 8080/85 based microcomputers by Gary Kildall of Digital Research, Inc. ...

Note that a file system can be extent-based (i.e., addressing via extents rather than in single blocks) without requiring that each file be limited to a single, contiguous extent.

See also

• Comparison of file systems

The following tables compare general and technical information for a number of file systems. ...

External links

• Getting to know the Solaris filesystem, Part 1: Allocation and storage strategy - comparison of block-based and extent-based allocation