Archive formats

An archive file is a file that is composed of one or more computer files along with metadata. Archive files are used to collect multiple data files together into a single file for easier portability and storage, or simply to compress files to use less storage space. Archive files often store directory structures, error detection and correction information, arbitrary comments, and sometimes use built-in encryption.

Archive files are particularly useful in that they store file system data and metadata within the contents of a particular file, and thus can be stored on systems or sent over channels that do not support the file system in question, only file contents – examples include sending a directory structure over email.

Beyond archival purposes, archive files are frequently used for packaging software for distribution, as software contents are often naturally spread across several files; the archive is then known as a . While the archival file format is the same, there are additional conventions about contents, such as requiring a manifest file, and the resulting format is known as a package format. Examples include deb for Debian, JAR for Java, and APK for Android.

Features supported by various kinds of archives include file concatenation, data compression, encryption, file spanning, checksums, self-extraction, self-installation, source volume and medium information, directory structure information, package notes and description, and other meta-data. The file extension or file header of the archive file are indicators of the file format used. Computer archive files are created by file archiver software, optical disc authoring software, and disk image software.

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