A flash file system considers the special abilities, performance and restrictions of flash memory devices. Frequently a disk file system can use a flash memory device as the underlying storage media but it is much better to use a file system specifically designed for a flash device. A tape file system is a file system and tape format designed to store files on tape. Magnetic tapes are sequential storage media with significantly longer random data access times than disks, posing challenges to the creation and efficient management of a general-purpose file system.
In a disk file system there is typically a master file directory, and a map of used and free data regions. Random access to data regions is measured in milliseconds so this system works well for disks. Tape requires linear motion to wind and unwind potentially very long reels of media.
Consequently, a master file directory and usage map can be extremely slow and inefficient with tape. Writing typically involves reading the block usage map to find free blocks for writing, updating the usage map and directory to add the data, and then advancing the tape to write the data in the correct spot.
Each additional file write requires updating the map and directory and writing the data, which may take several seconds to occur for each file. Tape file systems instead typically allow for the file directory to be spread across the tape intermixed with the data, referred to as streaming , so that time-consuming and repeated tape motions are not required to write new data.
However, a side effect of this design is that reading the file directory of a tape usually requires scanning the entire tape to read all the scattered directory entries. Most data archiving software that works with tape storage will store a local copy of the tape catalog on a disk file system, so that adding files to a tape can be done quickly without having to rescan the tape media. The local tape catalog copy is usually discarded if not used for a specified period of time, at which point the tape must be re-scanned if it is to be used in the future.
The Linear Tape File System uses a separate partition on the tape to record the index meta-data, thereby avoiding the problems associated with scattering directory entries across the entire tape. Writing data to a tape, erasing, or formatting a tape is often a significantly time-consuming process and can take several hours on large tapes.
This is due to the inherently destructive nature of overwriting data on sequential media. Because of the time it can take to format a tape, typically tapes are pre-formatted so that the tape user does not need to spend time preparing each new tape for use. All that is usually necessary is to write an identifying media label to the tape before use, and even this can be automatically written by software when a new tape is used for the first time.
Another concept for file management is the idea of a database-based file system. Instead of, or in addition to, hierarchical structured management, files are identified by their characteristics, like type of file, topic, author, or similar rich metadata. Around to Frank G. Soltis and his team at IBM Rochester have successfully designed and applied technologies like the database file system where others like Microsoft later failed to accomplish.
Some other projects that aren't "pure" database file systems but that use some aspects of a database file system:. Some programs need to either make multiple file system changes, or, if one or more of the changes fail for any reason, make none of the changes. If some of the writing fails and the software is left partially installed or updated, the software may be broken or unusable. An incomplete update of a key system utility, such as the command shell , may leave the entire system in an unusable state.
Transaction processing introduces the atomicity guarantee, ensuring that operations inside of a transaction are either all committed or the transaction can be aborted and the system discards all of its partial results. This means that if there is a crash or power failure, after recovery, the stored state will be consistent. Either the software will be completely installed or the failed installation will be completely rolled back, but an unusable partial install will not be left on the system.
Transactions also provide the isolation guarantee [ clarification needed ] , meaning that operations within a transaction are hidden from other threads on the system until the transaction commits, and that interfering operations on the system will be properly serialized with the transaction.
Ensuring consistency across multiple file system operations is difficult, if not impossible, without file system transactions. File locking can be used as a concurrency control mechanism for individual files, but it typically does not protect the directory structure or file metadata.
File locking also cannot automatically roll back a failed operation, such as a software upgrade; this requires atomicity. Journaling file systems is one technique used to introduce transaction-level consistency to file system structures. Journal transactions are not exposed to programs as part of the OS API; they are only used internally to ensure consistency at the granularity of a single system call.
Data backup systems typically do not provide support for direct backup of data stored in a transactional manner, which makes the recovery of reliable and consistent data sets difficult. Most backup software simply notes what files have changed since a certain time, regardless of the transactional state shared across multiple files in the overall dataset. As a workaround, some database systems simply produce an archived state file containing all data up to that point, and the backup software only backs that up and does not interact directly with the active transactional databases at all.
Recovery requires separate recreation of the database from the state file after the file has been restored by the backup software. A network file system is a file system that acts as a client for a remote file access protocol, providing access to files on a server. Programs using local interfaces can transparently create, manage and access hierarchical directories and files in remote network-connected computers. A shared disk file system is one in which a number of machines usually servers all have access to the same external disk subsystem usually a SAN.
The file system arbitrates access to that subsystem, preventing write collisions. A special file system presents non-file elements of an operating system as files so they can be acted on using file system APIs. This is most commonly done in Unix-like operating systems, but devices are given file names in some non-Unix-like operating systems as well. Examples in Unix-like systems include devfs and, in Linux 2.
In non-Unix-like systems, such as TOPS and other operating systems influenced by it, where the full filename or pathname of a file can include a device prefix, devices other than those containing file systems are referred to by a device prefix specifying the device, without anything following it.
In the s disk and digital tape devices were too expensive for some early microcomputer users. An inexpensive basic data storage system was devised that used common audio cassette tape. The system wrote a sound to provide time synchronization, then modulated sounds that encoded a prefix, the data, a checksum and a suffix. When the system needed to read data, the user was instructed to press "PLAY" on the cassette recorder. The system would listen to the sounds on the tape waiting until a burst of sound could be recognized as the synchronization.
The system would then interpret subsequent sounds as data. When the data read was complete, the system would notify the user to press "STOP" on the cassette recorder. It was primitive, but it mostly worked. Data was stored sequentially, usually in an unnamed format, although some systems such as the Commodore PET series of computers did allow the files to be named.
Multiple sets of data could be written and located by fast-forwarding the tape and observing at the tape counter to find the approximate start of the next data region on the tape. The user might have to listen to the sounds to find the right spot to begin playing the next data region. Some implementations even included audible sounds interspersed with the data.
In a flat file system, there are no subdirectories ; directory entries for all files are stored in a single directory. When floppy disk media was first available this type of file system was adequate due to the relatively small amount of data space available. These user areas were no more than special attributes associated with the files; that is, it was not necessary to define specific quota for each of these areas and files could be added to groups for as long as there was still free storage space on the disk.
It was unusual in that the file management program Macintosh Finder created the illusion of a partially hierarchical filing system on top of EMFS. This structure required every file to have a unique name, even if it appeared to be in a separate folder. While simple, flat file systems become awkward as the number of files grows and makes it difficult to organize data into related groups of files.
A recent addition to the flat file system family is Amazon 's S3 , a remote storage service, which is intentionally simplistic to allow users the ability to customize how their data is stored. The only constructs are buckets imagine a disk drive of unlimited size and objects similar, but not identical to the standard concept of a file. Many operating systems include support for more than one file system.
Sometimes the OS and the file system are so tightly interwoven that it is difficult to separate out file system functions. There needs to be an interface provided by the operating system software between the user and the file system. This interface can be textual such as provided by a command line interface , such as the Unix shell , or OpenVMS DCL or graphical such as provided by a graphical user interface , such as file browsers.
If graphical, the metaphor of the folder , containing documents, other files, and nested folders is often used see also: directory and folder. Unix-like operating systems create a virtual file system, which makes all the files on all the devices appear to exist in a single hierarchy.
This means, in those systems, there is one root directory , and every file existing on the system is located under it somewhere. Unix-like systems can use a RAM disk or network shared resource as its root directory. Unix-like systems assign a device name to each device, but this is not how the files on that device are accessed. Instead, to gain access to files on another device, the operating system must first be informed where in the directory tree those files should appear.
This process is called mounting a file system. It may be empty, or it may contain subdirectories for mounting individual devices. Generally, only the administrator i. Unix-like operating systems often include software and tools that assist in the mounting process and provide it new functionality. Some of these strategies have been coined "auto-mounting" as a reflection of their purpose. SquashFS is a common compressed read-only file system.
Solaris in earlier releases defaulted to non-journaled or non-logging UFS for bootable and supplementary file systems. Solaris defaulted to, supported, and extended UFS. Support for other file systems and significant enhancements were added over time, including Veritas Software Corp. Multiple operating systems including Solaris may use Veritas Volume Manager.
Modern Solaris based operating systems eclipse the need for volume management through leveraging virtual storage pools in ZFS. Later versions of HFS Plus added journaling to prevent corruption of the file system structure and introduced a number of optimizations to the allocation algorithms in an attempt to defragment files automatically without requiring an external defragmenter.
Filenames can be up to characters. HFS Plus uses Unicode to store filenames. On macOS, the filetype can come from the type code , stored in file's metadata, or the filename extension. Aliases are designed to maintain a link to their original file even if they are moved or renamed; they are not interpreted by the file system itself, but by the File Manager code in userland.
Newer versions of macOS are capable of reading and writing to the legacy FAT file systems 16 and 32 common on Windows. Mac OS X A journaled filesystem JFS was shipped in Plan 9 from Bell Labs treats everything as a file and accesses all objects as a file would be accessed i.
The 9P protocol removes the difference between local and remote files. File systems in Plan 9 are organized with the help of private, per-process namespaces, allowing each process to have a different view of the many file systems that provide resources in a distributed system. The Inferno operating system shares these concepts with Plan 9. Windows uses a drive letter abstraction at the user level to distinguish one disk or partition from another.
Drive C: is most commonly used for the primary hard disk drive partition, on which Windows is usually installed and from which it boots. This "tradition" has become so firmly ingrained that bugs exist in many applications which make assumptions that the drive that the operating system is installed on is C. The use of drive letters, and the tradition of using "C" as the drive letter for the primary hard disk drive partition, can be traced to MS-DOS , where the letters A and B were reserved for up to two floppy disk drives.
The FAT file systems are therefore well-suited as a universal exchange format between computers and devices of most any type and age. Various features have been added to the file system including subdirectories , codepage support, extended attributes , and long filenames. Most of these extensions are not supported by Windows.
The FAT12 and FAT16 file systems had a limit on the number of entries in the root directory of the file system and had restrictions on the maximum size of FAT-formatted disks or partitions. This is commonly referred to as the 8. Other features also supported by NTFS include hard links, multiple file streams, attribute indexing, quota tracking, sparse files, encryption, compression, and reparse points directories working as mount-points for other file systems, symlinks, junctions, remote storage links.
The system was designed to easily support removable disk packs , so the information relating to all files on one disk volume in IBM terminology is stored on that disk in a flat system file called the Volume Table of Contents VTOC. The VTOC stores all metadata for the file. Later a hierarchical directory structure was imposed with the introduction of the System Catalog , which can optionally catalog files datasets on resident and removable volumes.
The catalog only contains information to relate a dataset to a specific volume. If the user requests access to a dataset on an offline volume, and they have suitable privileges, the system will attempt to mount the required volume. Cataloged and non-cataloged datasets can still be accessed using information in the VTOC, bypassing the catalog, if the required volume id is provided to the OPEN request. Still later the VTOC was indexed to speed up access.
File data and control information are scattered and intermixed. Originally CMS used fixed-length byte blocks, but later versions used larger size blocks up to 4K. Access to a data record requires two levels of indirection , where the file's directory entry called a File Status Table FST entry points to blocks containing a list of addresses of the individual records.
Many types of objects are defined including the directories and files found in other file systems. It may be advantageous or necessary to have files in a different file system than they currently exist. Reasons include the need for an increase in the space requirements beyond the limits of the current file system. The depth of path may need to be increased beyond the restrictions of the file system.
There may be performance or reliability considerations. Providing access to another operating system which does not support the existing file system is another reason. In some cases conversion can be done in-place, although migrating the file system is more conservative, as it involves a creating a copy of the data and is recommended.
Migration has the disadvantage of requiring additional space although it may be faster. The best case is if there is unused space on media which will contain the final file system. For example, to migrate a FAT32 file system to an ext2 file system. First create a new ext2 file system, then copy the data to the file system, then delete the FAT32 file system.
An alternative, when there is not sufficient space to retain the original file system until the new one is created, is to use a work area such as a removable media. This takes longer but a backup of the data is a nice side effect. In hierarchical file systems, files are accessed by means of a path that is a branching list of directories containing the file.
Different file systems have different limits on the depth of the path. File systems also have a limit on the length of an individual filename. Copying files with long names or located in paths of significant depth from one file system to another may cause undesirable results. This depends on how the utility doing the copying handles the discrepancy.
From Wikipedia, the free encyclopedia. Format or program for storing files and directories. This article is about the way computers organise data stored on media such as disk. For library and office filing systems, see Library classification. An example of slack space, demonstrated with 4, byte NTFS clusters: , files, each five bytes per file, which equal to , bytes of actual data but require ,, bytes of disk space to store.
Main article: Filename. Main article: Directory file systems. Main article: Flash file system. Main article: Distributed file system. Main article: Shared disk file system. Not to be confused with Flat file database. Main article: File Allocation Table. Main article: NTFS. Main article: exFAT. Main article: Files Main article: CMS file system. Comparison of file systems Disk quota List of file systems List of Unix commands Directory structure Disk sharing Distributed file system Distributed Data Management Architecture File manager File system fragmentation Filename extension Global filesystem Object storage Physical and logical storage Storage efficiency Virtual file system.
The Linux Document Project. Retrieved December 11, A filesystem is the methods and data structures that an operating system uses to keep track of files on a disk or partition; that is, the way the files are organized on the disk. September 20, Office Practice and Business Procedure. Gregg Publishing Company. Retrieved August 1, Technical investigations of addition of a hardcopy output to the elements of a mechanized library system : final report, 20 Sept. Cincinnati, OH: Svco Corporation.
OCLC American Data Processing. Retrieved July 31, IBM Knowledge Center. Daley; P. Neumann Fall Joint Computer Conference. Retrieved Chandra Operating Systems. ISBN The word dentry is short for 'directory entry'. A dentry is nothing but a specific component in the path from the root.
They directory name or file name provide for accessing files or directories[. Retrieved 29 April Retrieved 8 February Archived from the original on 16 March Retrieved 6 February Apple Support. Microsoft Docs. Frequently Given Answers. Retrieved February 9, Retrieved February 21, Apple Inc. Retrieved September 22, In PHP 4.
For cases like described above, both will fail. It is not performing a pattern-like test on the parameter given. Its testing to see if the given parameter leads to a specific existing 'name. Maybe this is a newbie mistake, but note that paths are relative to the filesystem and the location of the script.
BTW, each successive call to dirname takes you one step up in the directory tree. This is actually a bug but I dont think there is an easy workaround. Try to switch to 64 bit. I do a lot of file parsing and have found the following technique extremely useful: while false! It also allows you to extend the usefulness of the above method by adding the ability to determine file types e. Well, it works but you are not guaranteed the file extension using that method.
A dirty and incomplete hack is below, incomplete because it never includes links and I never tested what happens when a directory is not allowed to be read. Please be aware wildcards do not work as one might expect.
For cases like described above, both will fail. It is not performing a pattern-like test on the parameter given. Its testing to see if the given parameter leads to a specific existing 'name. Maybe this is a newbie mistake, but note that paths are relative to the filesystem and the location of the script. BTW, each successive call to dirname takes you one step up in the directory tree. This is actually a bug but I dont think there is an easy workaround.
Try to switch to 64 bit. I do a lot of file parsing and have found the following technique extremely useful: while false! I do a lot of file parsing and have found the following technique extremely useful: while false! It also allows you to extend the usefulness of the above method by adding the ability to determine file types e. Sep Well, it works but you are not guaranteed the file extension using that method.
Oct Noting this since I sat with the problem for some time, cheers, Toxik. Aug Maybe this is a newbie mistake, but note that paths are relative to the filesystem and the location of the script. BTW, each successive call to dirname takes you one step up in the directory tree. Jun This is actually a bug but I dont think there is an easy workaround. Try to switch to 64 bit. It is not performing a pattern-like test on the parameter given.
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The name of the file is sent as a parameter to the is_file() function and it returns True if the file is a regular file else it returns False. michaelkorstote.com › php-is_file-function. Returns true if the filename exists and is a regular file, false otherwise. Note: Because PHP's integer type is signed and many platforms use 32bit integers.