ZIP
A zip archive in WinZip
File extension:	.zip
MIME type:	application/zip
Uniform Type Identifier:	com.pkware.zip-archive
Magic:	PK003004
Developed by:	Phil Katz
Type of format:	Data compression

The ZIP file format is a popular data compression and archival format. A ZIP file contains one or more files that have been compressed, to reduce their file size, or stored as-is. Screengrab of WinZip 8. ... WinZip Computing Inc. ... A filename extension is a suffix to the name of a computer file applied to show its format. ... Multipurpose Internet Mail Extensions (MIME) is an Internet Standard that extends the format of e-mail to support text in character sets other than US-ASCII, non-text attachments, multi-part message bodies, and header information in non-ASCII character sets. ... A Uniform Type Identifier (UTI) is a string that uniquely identifies the type of a class of items. ... In computer programming, a magic number is a constant used to identify the file or data type employed. ... Phil Katz, shown in 1994, holds a computer disk containing compression software made by his company, PKWare Inc. ... In computer science and information theory, data compression or source coding is the process of encoding information using fewer bits (or other information-bearing units) than an unencoded representation would use through use of specific encoding schemes. ... A file format is a particular way to encode information for storage in a computer file. ... In computer science and information theory, data compression or source coding is the process of encoding information using fewer bits (or other information-bearing units) than an unencoded representation would use through use of specific encoding schemes. ... A file archiver combines a number of files together into one archive file, or a series of archive files, for easier transportation or storage. ... A file format is a particular way to encode information for storage in a computer file. ...

The format was originally designed by Phil Katz for PKZIP. However, many software utilities other than PKZIP itself are now available to create, modify, or open (unzip, decompress) ZIP files, notably WinZip, BOMArchiveHelper, KGB Archiver, PicoZip, Info-ZIP, WinRAR, IZArc, 7-Zip, ALZip and TUGZip. Microsoft has included built-in ZIP support (under the name "compressed folders") in later versions of its Windows operating system. Apple has included built-in ZIP support in Mac OS X 10.3 and later via the BOMArchiveHelper utility. Phil Katz, shown in 1994, holds a computer disk containing compression software made by his company, PKWare Inc. ... PKZIP is an archiving tool originally written by the late Phil Katz, and marketed by his company PKWARE, Inc. ... WinZip Computing Inc. ... BOMArchiveHelper is the default archive file handler in Mac OS X. It is a service application that has no GUI when double-clicked, rather it is invoked by opening its associated files or by choosing Create archive of file in the Finders contextual menu. ... KGB Archiver is an open-source file archiver and data compression utility created by Tomasz Pawlak. ... PicoZip is a compression utility for Microsoft Windows users, developed by Acubix. ... Info-ZIP is an open source version of Phil Katzs deflate and inflate routines used in his popular file compression program, PKZIP. The free code released by the Info-ZIP project under a BSD license spawned a horde of PKZIP imitators (WinZip, PicoZip, PowerArchiver, Turbozip, PowerZip and many more... WinRAR is a shareware file archiver and data compression utility by Eugene Roshal. ... IZArc is a freeware file archiver for Microsoft Windows. ... 7-Zip is an open source file archiver designed originally for the Microsoft Windows operating system, and later made available to other systems. ... ALZip is an archive and compression utility from ESTsoft for Microsoft Windows. ... TUGZip is a freeware file archiver for Microsoft Windows. ... Microsoft Windows is the name of several families of proprietary software operating systems by Microsoft. ... An operating system (OS) is a set of computer programs that manage the hardware and software resources of a computer. ... Mac OS X (official IPA pronunciation: ) is a line of proprietary, graphical operating systems developed, marketed, and sold by Apple Inc. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... BOMArchiveHelper is the default archive file handler in Mac OS X. It is a service application that has no GUI when double-clicked, rather it is invoked by opening its associated files or by choosing Create archive of file in the Finders contextual menu. ...

ZIP files generally use the file extensions ".zip" or ".ZIP" and the MIME media type application/zip. Some software uses the ZIP file format as a wrapper for a large number of small items in a specific structure. Generally when this is done a different file extension is used. Examples of this usage are Java JAR files, id Software .pk3/.pk4 files, package files for StepMania and Winamp/Windows Media Player skins, XPInstall, as well as OpenDocument and Office Open XML office formats. Both OpenDocument and Office Open XML formats use the JAR file format internally, so files can be easily uncompressed and compressed using tools for ZIP files. A filename extension or filename suffix is an extra set of (usually) alphanumeric characters that is appended to the end of a filename to allow computer users (as well as various pieces of software on the computer system) to quickly determine the type of data stored in the file. ... Multipurpose Internet Mail Extensions (MIME) is an Internet Standard that extends the format of e-mail to support text in character sets other than US-ASCII, non-text attachments, multi-part message bodies, and header information in non-ASCII character sets. ... Java is an object-oriented applications programming language developed by Sun Microsystems in the early 1990s. ... In computing, a Jar file (short for Java archive) is a ZIP file used to distribute a set of Java classes. ... id Software (IPA: officially, though originally ) is an American computer game developer based in Mesquite, Texas, a suburb of Dallas. ... StepMania is a free/open source rhythm video game for Windows, Mac, and Linux created by Chris Danford. ... Winamp is a proprietary media player written by Nullsoft, a subsidiary of Time Warner. ... Windows Media Player (WMP) is a digital media player and media library application developed by Microsoft that is used for playing audio, video and images on personal computers running the Microsoft Windows operating system, as well as on Pocket PC and Windows Mobile-based devices. ... A typical XPInstall confirmation dialog XPInstall (Cross-Platform Install) is a technology used by Mozilla Application Suite, Mozilla Firefox, Mozilla Thunderbird and other XUL-based applications for installing Mozilla extensions that add functionality to the main application. ... OpenDocument or ODF, short for the OASIS Open Document Format for Office Applications, is a document file format used for describing electronic documents such as memos, reports, books, spreadsheets, charts, presentations and word processing documents. ... Office Open XML (commonly abbreviated as OOXML) is a file format specification for the storage of electronic documents such as memos, reports, books, spreadsheets, charts, presentations and word processing documents. ... OpenDocument or ODF, short for the OASIS Open Document Format for Office Applications, is a document file format used for describing electronic documents such as memos, reports, books, spreadsheets, charts, presentations and word processing documents. ... Office Open XML (commonly abbreviated as OOXML) is a file format specification for the storage of electronic documents such as memos, reports, books, spreadsheets, charts, presentations and word processing documents. ... In computing, a Jar file (short for Java archive) is a ZIP file used to distribute a set of Java classes. ...

History

Early history

The ZIP file format was originally created by Phil Katz, founder of PKWARE, after a prolonged legal dispute between PKWARE and System Enhancement Associates (SEA) over the trademark "ARC" (short for "Archive") and the file extension .ARC. Phil Katz, shown in 1994, holds a computer disk containing compression software made by his company, PKWare Inc. ... PKZIP is an archiving tool originally written by the late Phil Katz, and marketed by his company PKWARE, Inc. ... ARC is a file format by SEA (System Enhancement Associates) that was very popular before Phil Katzs introduction of the ZIP format. ...

PKWARE's first archive product, PKARC, borrowed heavily from SEA's published code, and improved on it by converting SEA's ARC C code into hand-optimised assembler, which was much faster. PKARC also used the ".ARC" file extension. SEA contended that Katz had based his product on their code and trademark, and thus ought to license the code from them and pay royalties. PKWARE refused. SEA brought a successful copyright infringement lawsuit against Phil Katz and PKWARE. After suit was brought, Katz briefly released a relabeled version of PKARC named PKPAK in a futile effort to invalidate the suit. C is a general-purpose, procedural, imperative computer programming language developed in 1972 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system. ...

During settlement, Katz still refused to pay license fees to SEA, instead agreeing to pay SEA's legal expenses and stop selling PKARC. He then went on to create his own file format, which is known worldwide now as the ZIP format (commonly called a "ZIP file"). The ZIP format was more resistant to data loss than the ARC format because of redundant catalog storage; it also was more flexible than ARC, providing room for additional optional compression algorithms and future expansion. Along with the new format, PKZIP included at least one compression algorithm more efficient than any supported by ARC. Once PKZIP was released, many users abandoned ARC because of its slower speed and less effective compression, and because Katz had successfully put forth the idea that he was the "good guy" who was being treated unfairly by an "evil corporation".

Katz publicly released technical documentation on the ZIP file format making it an open format, along with the first version of his PKZIP archiver, in January 1989. An open format is a published specification for storing digital data, usually maintained by a non-proprietary standards organization, and free of legal restrictions on use. ... 1989 (MCMLXXXIX) was a common year starting on Sunday of the Gregorian calendar. ...

The name zip (meaning speed) was suggested by Katz's friend Robert Mahoney. They wanted to imply that their product would be faster than ARC and other compression formats of the time.

Moving beyond the command line

In the mid 1990s, as more new computers included graphical user interfaces, more users were not comfortable with the command-line operation of PKZIP. Seeing an opportunity, shareware authors began pitching compression and archival programs with graphical user interfaces. Many of these used the ZIP format. WinZip was among the most popular. PKWARE also offered a graphical version of PKZIP. These programs were easier to learn than the older command-line equivalents, but users still had to learn a specialized tool with its own interface for file archival and compression. “PUI” redirects here. ... A command line interface or CLI is a method of interacting with a computer by giving it lines of textual commands (that is, a sequence of characters) either from keyboard input or from a script. ... Look up shareware in Wiktionary, the free dictionary. ... WinZip Computing Inc. ...

In the late 1990s, various file manager software started integrating support for the ZIP format into their user interface. Even earlier, Norton Commander and its clones like Volkov Commander in DOS had started that trend, and that remains the norm for the "Commander-like" or Orthodox file managers like Midnight Commander for Linux and UNIX-like systems and Total Commander (previously Windows Commander) for Windows. The KDE file manager (kfm) supported the ZIP format very early; ZIP support was also first added to Windows Explorer with the Plus! enhancement package in Windows 98 and later included in Windows Me and Windows XP; ZIP format support is also built in the Mac OS Finder (as of Mac OS X, via the BOMArchiveHelper utility), the Nautilus file manager used by GNOME and the Konqueror file manager of newer versions of KDE. By 2002, all major desktop environments included ZIP file support in their file managers: a ZIP file is typically presented as a directory or folder, so that files are copied into and out of it in the same manner as any other folder and the compression is handled in a way largely transparent to the user. This has eliminated the need to learn a specialized tool and interface for file archival and compression. A file manager is a computer program that provides a user interface to work with file systems. ... Pre-Symantec version of Norton Commander for DOS Norton Commander v. ... In the computer and video game industry, a clone is a game or game series which is very similar to or heavily inspired by a previous popular game or game series. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... Instructions on how to use the directory command. ... Orthodox File Managers (OFM), also known as Commander-like file managers, are the family of file managers based on the old Norton Commander interface. ... Midnight Commander (mc) is an orthodox file manager for Unix-like systems and a clone of Norton Commander. ... Total Commander is a shareware Orthodox File Manager (OFM) for Windows. ... KDE (K Desktop Environment) (IPA: ) is a free software project which aims to be a powerful ecosystem for an easy-to-use desktop environment. ... It has been suggested that this article or section be merged with Windows Shell. ... Microsoft Plus! is an operating system enhancement package provided by Microsoft. ... Windows 98 (codenamed Memphis) is a graphical operating system released on June 25, 1998 by Microsoft and the successor to Windows 95. ... Windows Millennium Edition, or Windows Me is a hybrid 16-bit/32-bit graphical operating system released on September 14, 2000 by Microsoft. ... Windows XP is a line of proprietary operating systems developed by Microsoft for use on general-purpose computer systems, including home and business desktops, notebook computers, and media centers. ... Finder may be: A device attached to a telescope which gives a much larger field of view than the main telescope and so allows an astronomer to centre the telescope on an object using crosshairs. ... Mac OS X (official IPA pronunciation: ) is a line of proprietary, graphical operating systems developed, marketed, and sold by Apple Inc. ... BOMArchiveHelper is the default archive file handler in Mac OS X. It is a service application that has no GUI when double-clicked, rather it is invoked by opening its associated files or by choosing Create archive of file in the Finders contextual menu. ... Genera Allonautilus Nautilus Nautilus (from Greek ναυτίλος, sailor) is the common name of any marine creatures of the cephalopod family Nautilidae, the sole family of the suborder Nautilina. ... This article or section does not adequately cite its references or sources. ... Konqueror is a file manager, web browser and file viewer, which was developed as part of the K Desktop Environment (KDE) by volunteers and runs on most Unix-like operating systems. ... For album titles with the same name, see 2002 (album). ... It has been suggested that Desktop metaphor,Paper paradigm be merged into this article or section. ...

Technical information

ZIP is a fairly simple archive format that compresses every file separately. Compressing files separately allows for individual files to be retrieved without reading through other data; in theory, it may allow better compression by using different algorithms for different files. However a caveat to this is that archives containing a large number of small files end up significantly larger than if they were compressed as a single file (the classic example of the latter is the common tar.gz archive which consists of a TAR archive compressed using gzip). Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... In computing, the tar (file) format (derived from tape archive) is a type of archive bitstream or file format. ... In computing, the tar (file) format (derived from tape archive) is a type of archive bitstream or file format. ... The correct title of this article is . ...

The specification for ZIP indicates that files can be stored either uncompressed or using a variety of compression algorithms. However, in practice, ZIP is almost always used with Katz's DEFLATE algorithm, except when files being added are already compressed or are resistant to compression. Phil Katz, shown in 1994, holds a computer disk containing compression software made by his company, PKWare Inc. ... DEFLATE is a lossless data compression algorithm that uses a combination of the LZ77 algorithm and Huffman coding. ... In mathematics, computing, linguistics, and related disciplines, an algorithm is a finite set of well-defined instructions for accomplishing some task which, given an initial state, will terminate in a defined end-state. ...

ZIP supports a simple password-based symmetric encryption system which is known to be seriously flawed. In particular it is vulnerable to known-plaintext attacks which are in some cases made worse by poor implementations of random number generators.^[1] It also supports spreading archives across multiple removable disks (generally floppy disks, but it could also be used with other removable media). A password is a form of secret authentication data that is used to control access to a resource. ... Symmetric-key algorithms are a class of algorithms for cryptography that use trivially related cryptographic keys for both decryption and encryption. ... The known-plaintext attack (KPA) is an attack model for cryptanalytic where the attacker has samples of both the plaintext and its encrypted version (ciphertext) and is at liberty to make use of them to reveal further secret information; typically this is the secret key. ... A random number generator is a computational or physical device designed to generate a sequence of elements (usually numbers), such that the sequence can be used as a random one. ... A floppy disk is a data storage device that is composed of a disk of thin, flexible (floppy) magnetic storage medium encased in a square or rectangular plastic shell. ...

New features including new compression and encryption (e.g. AES) methods have been added to ZIP in more recent times, but these are not supported by many tools and are not in wide use. In computer science and information theory, data compression or source coding is the process of encoding information using fewer bits (or other information-bearing units) than an unencoded representation would use through use of specific encoding schemes. ... This article is about algorithms for encryption and decryption. ... In cryptography, the Advanced Encryption Standard (AES), also known as Rijndael, is a block cipher adopted as an encryption standard by the U.S. government. ...

The original ZIP format had a number of limits (uncompressed size of a file, compressed size of a file and total size of the archive) at 4GB. In version 4.5 of the specification, PKWARE introduced the "ZIP64" format extensions to get around these limitations.

The FAT filesystem of DOS only has a timestamp resolution of two seconds; ZIP file records mimic this. As a result, the built-in timestamp resolution of files in a ZIP archive is only two seconds, though extra fields can be used to store more accurate timestamps. File Allocation Table (FAT) is a partially patented file system developed by Microsoft for MS-DOS and was the primary file system for consumer versions of Microsoft Windows up to and including Windows Me. ...

The Info-ZIP implementations of the ZIP format adds support for Unix filesystem features, such as user and group IDs, file permissions, and support for symbolic links. The Apache Ant implementation is aware of them to the extent that it can create files with predefined Unix permissions. Info-ZIP is an open source version of Phil Katzs deflate and inflate routines used in his popular file compression program, PKZIP. The free code released by the Info-ZIP project under a BSD license spawned a horde of PKZIP imitators (WinZip, PicoZip, PowerArchiver, Turbozip, PowerZip and many more... Apache Ant is a software tool for automating software build processes. ...

The Info-ZIP Windows tools also support NTFS filesystem permissions, and will make an attempt to translate from NTFS permissions to Unix permissions or vice-versa when extracting files. This is sometimes annoying, and can result in undesireable combinations, e.g. .exe files being created on NTFS volumes with executable permission denied. An executable or executable file, in computer science, is a file whose contents are meant to be interpreted as a program by a computer. ...

Compression methods

The size for comparison figures were made using the contents of ftp://ftp.kernel.org/pub/linux/kernel/v2.6/linux-2.6.9.tar.bz2 and maximum compression.

• Shrinking (method 1)

Shrinking is a variant of LZW with a few minor tweaks. As such it was affected by the LZW patent issue. It was never clear if the patent covered unshrinking but some open source projects (for example Info-ZIP) decided to play it safe and not include unshrinking support in the default builds.

• Reducing (methods 2-5)

Reducing involves a combination of compressing repeated byte sequences then applying a probability-based encoding to the result.

• Imploding (method 6)

Imploding involves compressing repeated byte sequences with a sliding window then compressing the result using multiple Shannon-Fano trees.

• Tokenizing (method 7)

This method number is reserved. The PKWARE specification does not define an algorithm for it. This is because the format was developed (as a non-proprietary open specification) by a third-party other than PKWARE for specialized usage.^{[citation needed]}

• Deflate and enhanced deflate (methods 8 and 9)

These methods use the well-known deflate algorithm. Deflate allows a window up to 32 KiB. Enhanced deflate allows a window up to 64 KiB. The enhanced version performs slightly better but is not as widely supported.

Sizes for comparison (using PKZIP 8.00.0038 for Windows):

• Deflate: 52.1 MiB
• Enhanced deflate: 51.8 MiB

• PKWARE Data Compression Library Imploding (method 10)

The official ZIP format specification gives no further information on this.

Size for comparison: 61.6 MiB (PKZIP 8.00.0038 for Windows in binary mode).

• Method 11

This method number is reserved by PKWARE.

• Bzip2 (method 12)

This method uses the well-known bzip2 algorithm. This algorithm performs better than deflate but is not widely supported, particularly by Windows-based tools.

Size for comparison: 50.6 MiB (PKZIP 8.00.0038 for Windows).

Note that although both the original (tar inside bzip2, 34.6 MiB) and the comparison version (bzip2 as a ZIP method, 50.6 MiB) use the same compression algorithm, the ZIP version is 46% larger. This demonstrates the compression ratio advantage of a solid archive over ZIP's strategy of compressing each individual file separately when used to archive many (16,448) files.

LZW (Lempel-Ziv-Welch) is an implementation of a lossless data compression algorithm created by Abraham Lempel and Jacob Ziv. ... A patent is a set of exclusive rights granted by a state to a patentee (the inventor or assignee) for a fixed period of time in exchange for the regulated, public disclosure of certain details of a device, method, process or composition of matter (substance) (known as an invention) which... Open source refers to projects that are open to the public and which draw on other projects that are freely available to the general public. ... Info-ZIP is an open source version of Phil Katzs deflate and inflate routines used in his popular file compression program, PKZIP. The free code released by the Info-ZIP project under a BSD license spawned a horde of PKZIP imitators (WinZip, PicoZip, PowerArchiver, Turbozip, PowerZip and many more... In signal processing, a window function (or apodization function) is a function that is zero-valued outside of some chosen interval. ... In the field of data compression, Shannon-Fano coding is a technique for constructing a prefix code based on a set of symbols and their probabilities (estimated or measured). ... DEFLATE is a lossless data compression algorithm that uses a combination of the LZ77 algorithm and Huffman coding. ... According to the International Electrotechnical Commission a kibibyte (a contraction of kilo binary byte) is a unit of information or computer storage. ... The three-letter acronym MIB may refer to any of several concepts: Management information base, a computing information repository used (for example) by SNMP In marbles, any marble, but esp. ... The correct title of this article is . ... In computing, solid compression refers to a method for data compression of multiple files, wherein all the compressed files are concatenated and treated as a single data block. ...

References

1. ^ Stay, Michael. "ZIP Attacks with Reduced Known Plaintext". http://math.ucr.edu/~mike/zipattacks.pdf

See also

• List of archive formats
• LZW compression method
• List of file archivers (programs that compress and decompress ZIP files)
• Comparison of file archivers (programs that compress and decompress ZIP files)

This is a list of file formats used by archivers and compressors. ... LZW (Lempel-Ziv-Welch) is an implementation of a lossless data compression algorithm created by Abraham Lempel and Jacob Ziv. ... It has been suggested that this article or section be merged into Comparison of file archivers. ... The following tables compare general and technical information for a number of file archivers. ...

External links

• Technical specifications of the PKZIP file formats from info-ZIP
• Current file format specification from PKWARE (including many recent features that are not widely supported)
• Original specification for the first version of the format
• List of ZIP-related resources, libraries and sources
• 18 Years of ZIP format: Happy Birthday at The Data Compression News Blog
• Comparison of the performances of various methods of data compression (french)
• Archive and compressed file types