ZIP

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Not to be confused with Zip disk, an unrelated disk cartridge unit.
File Format
Name ZIP
Ontology
Extension(s) .zip
MIME Type(s) application/zip
LoCFDD fdd000354, fdd000355, fdd000362, fdd000361
PRONOM x-fmt/263
UTI com.pkware.zip-archive
Released 1989

ZIP is one of the most popular file compression formats. It was created in 1989 as the native format of the PKZIP program, which was introduced by Phil Katz in the wake of a lawsuit (which he lost) against him by the makers of the then-popular ARC program (and file format) for copyright and trademark infringement in an earlier program PKARC which had been file-compatible with ARC. This resulted in Katz creating a new file format, which rapidly overtook ARC in popularity (to a large extent because of BBS sysops, then the primary users of such compression, resenting the lawsuit). Many programs have been released for a variety of operating systems to compress and decompress ZIP files, and native support for the format is built into several popular operating systems.

ZIP implementations vary in their support for features in the specification from PKWARE[1], particularly features added since version 2 (1993), some of which are protected by patents and require licensing. Many implementations limit the use of compression to the DEFLATE algorithm, introduced with version 2. Extensions incorporated into the specification that have been widely adopted are: long filenames; large files (using a technique known as ZIP64); and filenames in UTF-8. In 2011 work began on an interoperable subset of the latest APPNOTE.TXT with the intention of publication as ISO/IEC 21320-1, Document Container File -- Part 1: Core. As of November 2012, a discussion draft is available[2]. Designed to promote interoperable implementations, the draft ISO/IEC 21320-1 prohibits compression other than using DEFLATE, segmentation or multiple volumes, and features that are subject to patents.

While .zip is the usual file extension, ZIP-formatted files can be found with many other extensions since a number of other file formats use ZIP compression but store their files in application-specific extensions. See Category:ZIP based file formats for a list of such formats.

Contents

See also

Identification

The byte sequence 'P' 'K' 0x05 0x06 (the "end of central directory signature") appears in the last 22 bytes of the file.

Most ZIP files begin with 'P' 'K' 0x03 0x04 (and some ZIP-based formats are required to), but self-extracting ZIP files do not.

Specifications

Software

References

  1. http://www.pkware.com/documents/casestudies/APPNOTE.TXT
  2. http://kikaku.itscj.ipsj.or.jp/sc34/open/1855.pdf

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