Archive file
File with the content of one or more files with their associated metadata From Wikipedia, the free encyclopedia
In computing, an archive file stores the content of one or more files, possibly compressed, with associated metadata such as file name, directory structure, error detection and correction information, commentary, compressed data archives, storage, and sometimes encryption. An archive file is often used to facilitate portability, distribution and backup, and to reduce storage use.[1][2][3]
Applications
Portability
As an archive file stores file system information, including file content and metadata, it can be leveraged for file system content portability across heterogeneous systems. For example, a directory tree can be sent via email, files with unsupported names on the target system can be renamed during extraction, timestamps can be retained rather than lost during data transmission.[4] Also, transfer of a single archive file may be faster than processing multiple files due to per-file overhead,[5][6] and even faster if compressed.
Software distribution
Beyond archiving, archive files are often used for software distribution. When used in connection with a package manager, an archive must conform to a package format and is called a package. In particular, the format usually requires a manifest file.[7] Examples include deb for Debian, JAR for Java, APK for Android, and self-extracting Windows Installer executables.
Features
Notable features supported for various archives include:
- Concatenate multiple files in a single file
- Store file metadata as data, including file name, timestamps, permissions, source storage, notes and description
- Compression
- Encryption
- Error detection via checksums
- Error correction code to fix errors
- Splitting a large file into multiple, smaller files
- File patches/updates (when recording changes since a previous archive)
- Self-extraction
- Self-installation
Error detection and recovery
Archive files often include parity checks and other checksums for error detection, for instance zip files use a cyclic redundancy check (CRC). RAR archives may include additional error correction data (called recovery records).[8]
Archive files that do not natively support recovery records can use separate parchive (PAR) files that allows for additional error correction and recovery of missing files in a multi-file archive.[9]
Format
The format of an archive file is its archive format. Some formats are well-defined and some have become conventions supported by multiple vendors and communities.[10] As is common for all files, the format of an archive is generally indicated by file name extension and/or file header.[11]
Commonly used formats include zip, rar, 7z, and tar.[12] Java introduced archive formats including jar (j for Java) and war (w for web) that store an entire runnable deployment; usually compressed.[13]
See also
- Comparison of archive formats
- Digital container format – Metafile format
- Disk image – Computer file consisting of the contents of a storage device
- File archiver – Utility software for combining files
- List of archive formats
References
External links
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