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File archiving is used to collect multiple files together into a single file for easier portability, storage, or sharing. Archiving is also used to compress files in order to save disk space or for faster uploading.

Archiving is often used to package software for distribution, since software programs generally include several files, including documentation. The archive is known as a package.

A file archiver is a computer application that combines these files together into one archive file or, in some cases, a series of archive files. File archivers often use lossless data compression in order to reduce the size of the archive. For a proper reconstruction of the archived files to take place, the archiver stores metadata, or at least the names and lengths of the original files, while many archivers store additional metadata, including the original timestamps, file attributes, and access control files. The process of producing an archive file is called archiving or packing, while the process of reconstructing the original files from the archive is known as unarchiving, unpacking, or extracting.

Data compression is the process of encoding information so that the resulting file uses fewer bits than the original file. As used by a file archiver, the resulting file will usually be smaller than the sum of the individual files that it contains.

File compression can be lossy or lossless. Lossy compression reduces the number of bits by removing unnecessary or less important information. In the case of image files, some loss of information may be acceptable, but there is a tradeoff between preserving information and reducing the size of the file, as the loss of data is not reversible. This is not as likely to be acceptable when it comes to archiving computer software programs.

Lossless data compression algorithms use statistical redundancy to represent data without loss of information so that the process is reversible. There are several schemes to reduce file size, largely by eliminating redundancy.

Archive formats used for archiving only include A, AR, CPIO, ISO, LBR, MAR, SBX, SHAR, and TAR.

Those used for compression only include ?XF, BZ2, F, GZ, LZ, LZMA, LZO, RZ, SFARK, SZ, ?Q?, ?Z?, YZ, Z, and ??_.

Archive formats used for both archiving and compression are 7Z, ACE, AFA, ALZ, APK, ARC, ARJ, B1, B6Z, BA, BH, CAB, CAR, CDX, CFS, CPT, DAR, DD, DGC, DMG, EAR, GCA, HA, HKI, ICE, JAR, KGB, LHA, LZH, LZX, PAK, PARTIMG, PAQ6, PAQ7, PAQ8, PEA, PIM, PIT, QDA, RAR, RK, S7Z, SDA, SEA, SEN, SFX, SHK, SIT, SITX, SQX, TAR.BZ2, TAR.GZ, TAR.IZ, TAR.XZ, TAR.Z, TBZ2, TGZ, TIZ, TYZ, UC, UCA, UC0, UC2, UCN, UE2, UHA, UR2, WAR, WIM, XAR, XP3, YZ1, ZIP, ZIPX, ZOO, ZPAQ, and ZZ.

One of the most common file formats for archiving is ZIP. Around since 1989, ZIP was first implemented in PKWARE's PKZIP utility, as a replacement for the ARC compression format, and has quickly been supported by several other utilities and software companies, including Microsoft and Apple. The ZIP format supports lossless data compression and permits a number of compression algorithms. Although there are several file archivers using ZIP technology, they generally use the ZIP file extension, and archives created through ZIP are often represented by an icon that features a zipper.

File archivers and compression utilities are the focus of topics in this category.



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