NationMaster - Encyclopedia: Fork (filesystem)

In computer file systems, a fork is additional data associated with a file system object. A file system might support only one fork per file or might support multiple named forks. Unlike extended attributes, which are typically limited in size, a fork can be of arbitrary size, possibly even larger than the file's data. For library and office filing systems, see Library classification. ... Extended file attributes is a filesystem feature that enables users to associate arbitrary metadata with computer files, whereas regular attributes have a strictly defined purpose (such as permissions or records of creation and modification times). ...

File system forks are traditionally associated with Apple's Hierarchical File System (HFS),^[1] but are also available in other file systems. In Microsoft's NTFS they are known as Alternate Data Streams (ADS).^[2] Other filesystems such as Novell's Novell Storage Services (NSS) and NetWare File System (NWFS), Solaris's UFS (in Solaris 9 and later)^[3] and ZFS, and Veritas Software's Veritas File System (VxFS) also support file system forks. In Solaris they are known as "extended attributes", although they can be as large as a file and are accessed in the same way a file's data is and thus behave like a fork. UDF, being a universal file system for general data exchange, supports forks as well. Apple Inc. ... 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. ... Microsoft Corporation, (NASDAQ: MSFT, HKSE: 4338) is a multinational computer technology corporation with global annual revenue of US$44. ... NTFS is the standard file system of Windows NT, including its later versions Windows 2000, Windows XP, Windows Server 2003, Windows Server 2008, and Windows Vista. ... Novell was also the name of a road bicycle racing team. ... Novell Storage Services (NSS) is a file system used by Novells NetWare Operating system and recently ported to Linux. ... NetWare File System (NWFS), is a file system, based on a heavily-modified version of FAT. It was used in the Novell NetWare operating system. ... Solaris is a computer operating system developed by Sun Microsystems. ... The UNIX file system (UFS) is a file system used by many Unix and Unix-like operating systems. ... In computing, ZFS is a file system originally created by Sun Microsystems for the Solaris Operating System. ... VERITAS Software Corp. ... 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. ... The Universal Disk Format (UDF) is a format specification of a file system for storing files on optical media. ...

Apple's HFS, and the original Apple Macintosh file system MFS, were designed to allow a file to have a resource fork to store metadata that would be used by the system's graphical user interface (GUI), such as a file's icon to be used by the Finder or the menus and dialog boxes associated with an application.^[4] However the feature was not limited to GUI data, so additional uses were found, such as splitting a word processing document into content and presentation, then storing the presentation information in the resource fork. One particular non-obvious use is that prior to Mac OS X, PostScript Type 1 fonts have traditionally been stored entirely in the resource fork, the data fork being empty^[5]. In addition, old 680x0 applications had all of their code in the resource fork as 32K segments which were loaded on demand^[6]. The first Macintosh computer, introduced in 1984, upgraded to a 512K Fat Mac. The Macintosh or Mac, is a line of personal computers designed, developed, manufactured, and marketed by Apple Computer. ... This article is about the MFS file system. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... Metadata is data about data. ... GUI redirects here. ... Mac OS X (pronounced ) is a line of graphical operating systems developed, marketed, and sold by Apple Inc. ... For the literary term, see Postscript. ... PostScript (PS) is a page description language used primarily in the electronic and desktop publishing areas. ...

Starting in 1985, NWFS and its successor NSS were designed from the ground up to use a variety of methods to store a file's metadata. Some metadata resides in Novell Directory Services (NDS), some is stored in the directory structure on the disk, and some is stored in, as Novell terms it, 'multiple data streams' with the file itself. Multiple data streams also allow Macintosh clients to attach to and use NetWare servers. This article is about the year. ... Novell eDirectory (formerly called Novell Directory Services) is an X.500 compatible directory service software product released in 1993 by Novell, Inc. ... NetWare is a network operating system and the set of network protocols it uses to talk to client machines on the network. ...

In 1993, Microsoft released the first version of the Windows NT operating system which introduced the NTFS filesystem. This filesystem includes support for multiple named forks as alternate data streams for compatibility with pre-existing operating systems that support forks. With Windows 2000, Microsoft started using alternate data streams in NTFS to store things such as author or title file attributes^[7] and image thumbnails.^[8] With Service Pack 2 for Windows XP, Microsoft introduced the Attachment Execution Service that stores details on the origin of downloaded files in alternate data streams attached to files, in an effort to protect users from downloaded files that may present a risk.^[9] Year 1993 (MCMXCIII) was a common year starting on Friday (link will display full 1993 Gregorian calendar). ... Windows NT (New Technology) is a family of operating systems produced by Microsoft, the first version of which was released in July 1993. ... NTFS is the standard file system of Windows NT, including its later versions Windows 2000, Windows XP, Windows Server 2003, Windows Server 2008, and Windows Vista. ... Windows 2000 (also referred to as Win2K) is a preemptive, interruptible, graphical and business-oriented operating system designed to work with either uniprocessor or symmetric multi-processor computers. ... The ThumbsPlus image file manager showing folder tree in the upper left and 12 thumbnail-size images to the right. ... Windows XP is a line of operating systems developed by Microsoft for use on general-purpose computer systems, including home and business desktops, notebook computers, and media centers. ...

Possible security and data loss risks with forks

When a filesystem supports different forks, the applications should be aware of them, or security risks can arise.

If the different system utilities (disk explorer, antivirus software, archivers, and so on), are not aware of the different forks, the following problems can arise:

Windows NT versions include the ability to use forks in the API, and some command line tools can be used to create and access forks, but they are ignored by most programs, including Windows Explorer and the DIR command. Windows Explorer copies forks and warns when the target file system doesn't support them, but only counts the main fork's size and it doesn't list a file or folder's streams. The DIR command has been updated in Vista to include an option that will list forks.^[10] Until Mac OS X v10.4, users using the Unix command line utilities (such as tar) included with Mac OS X would risk data loss, as the utilities were not updated to handle the resource forks of files until v10.4^[11]. A computer virus is a computer program that can copy itself and infect a computer without permission or knowledge of the user. ... Wikipedia does not yet have an article with this exact name. ... Windows Explorer running on Windows Vista Windows Explorer running on Windows XP Windows Explorer is an application that is part of modern versions of the Microsoft Windows operating system that provides a graphical user interface for accessing the file systems. ... In computing, dir is a command used for file and directory listing, specifically in CP/M and the command line interface (CLI) of the DOS operating system. ... Mac OS X version 10. ... Filiation of Unix and Unix-like systems Unix (officially trademarked as UNIXÂ®, sometimes also written as or Â® with small caps) is a computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs including Ken Thompson, Dennis Ritchie and Douglas McIlroy. ... In computing, tar (derived from tape archive) is both file format (in the form of a type of archive bitstream) and the name of the program used to handle such files. ... Mac OS X (pronounced ) is a line of graphical operating systems developed, marketed, and sold by Apple Inc. ...

See also

Extended file attributes is a file system feature that enables users to associate computer files with metadata not interpreted by the filesystem, whereas regular attributes have a purpose strictly defined by the filesystem (such as permissions or records of creation and modification times). ...

References

^ Apple (July 2, 1996). File Forks. Apple. Retrieved on 2006-11-18.
^ Microsoft. Files and Clusters. Microsoft. Retrieved on 2006-11-18.
^ Sun. What's New in the Solaris 9 8/03 Operating Environment: File System Enhancements. Sun. Retrieved on 2006-11-18.
^ Bruce Horn. The Grand Unified Model (1) - Resources. Folklore.org. Retrieved on 2006-11-18.
^ Adobe (July 7, 2004). PostScript Type 1 and Type 3 Fonts General Information. Adobe. Retrieved on 2006-11-18.
^ Andy Hertzfeld. RMaker. Folklore.org. Retrieved on 2006-11-18.
^ Dino Esposito (March 2000). A Programmer's Perspective on NTFS 2000 Part 1: Stream and Hard Link. Microsoft. Retrieved on 2006-11-18.
^ Microsoft (October 27, 2006). Indexing service adds data streams to image files. Microsoft. Retrieved on 2006-11-18.
^ Bart De Smet (August 19, 2005). Demo of "Attachment Execution Service internals" in Windows XP SP2 and Windows Server 2003 SP1. B# .NET Blog. Retrieved on 2006-11-18.
^ Bart De Smet (July 13, 2006). Use Vista's DIR command to display alternate data streams. B# .NET Blog. Retrieved on 2007-07-07.
^ Command-line Backup Solutions on Mac OS X. Apple (October 29, 2005). Retrieved on 2006-11-18.

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