ZIP (file format)

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Introduction, History, and Standardization of ZIP file format
– ZIP is an archive file format that supports lossless data compression.
– ZIP files may contain compressed files or directories.
– The format was created in 1989 as a replacement for the ARC compression format.
– The ZIP file format was designed by Phil Katz and Gary Conway.
– The format proliferated widely on the internet during the 1990s.
– ISO/IEC 21320-1 Document Container File — Part 1: Core was published in 2015, stating that document container files are conforming Zip files.
– The standard restricts certain features and prohibits encryption, digital signatures, and patched data features.

Version history and features of ZIP file format
– The ZIP File Format Specification has its own version number.
– Key advances in various versions include support for Deflate64 compression, AES encryption, Unicode filename storage, and expanded compression algorithms.
– The latest version is 6.3.10, released in 2022, which added z/OS attribute values and additional 3rd party Extra Field mappings.

ZIP file structure and internal layout
– ZIP files allow for random-access processing without compressing or decompressing the entire archive.
– A directory is placed at the end of a ZIP file, identifying the files and their locations.
– ZIP archives can include extra data unrelated to the archive itself, allowing for self-extracting archives.
– The order of file entries in the central directory does not have to coincide with the order in the archive.
– ZIP files are identified by the presence of an end of central directory record.
– Local file headers provide redundancy by including the same information as the central directory.
– ZIP files can be updated by appending new files and an updated central directory.

ZIP file signatures, headers, and timestamps
– Each entry in a ZIP archive is introduced by a local file header with file information and optional extra data fields.
– Extra data fields are used to support ZIP64 format, encryption, file attributes, and higher-resolution timestamps.
– The ZIP format uses specific 4-byte signatures to denote various structures in the file.
– ZIP archives can be spread across multiple file-system files for storage or transmission purposes.
– The timestamp resolution of files in a ZIP archive is limited to two seconds, matching the FAT filesystem of DOS.

Compression methods, encryption, ZIP64 support, and compatibility
– The ZIP format supports various compression methods, with DEFLATE being the most common.
– ZIP supports a password-based symmetric encryption system known as ZipCrypto.
– ZIP64 format extensions were introduced to overcome the 4GB limit of the original ZIP format.
– Support for ZIP64 varies across different software and operating systems.
– Some extension libraries and tools support ZIP64, while others may not.

ZIP (file format) (Wikipedia)

ZIP is an archive file format that supports lossless data compression. A ZIP file may contain one or more files or directories that may have been compressed. The ZIP file format permits a number of compression algorithms, though DEFLATE is the most common. This format was originally created in 1989 and was first implemented in PKWARE, Inc.'s PKZIP utility, as a replacement for the previous ARC compression format by Thom Henderson. The ZIP format was then quickly supported by many software utilities other than PKZIP. Microsoft has included built-in ZIP support (under the name "compressed folders") in versions of Microsoft Windows since 1998 via the "Plus! 98" addon for Windows 98. Native support was added as of the year 2000 in Windows ME.[citation needed] Apple has included built-in ZIP support in Mac OS X 10.3 (via BOMArchiveHelper, now Archive Utility) and later. Most free operating systems have built in support for ZIP in similar manners to Windows and macOS.

ZIP file format
Filename extension.zip .zipx .z01 .zx01
Internet media typeapplication/zip
Uniform Type Identifier (UTI)com.pkware.zip-archive
Magic number
  • none
  • PK\x03\x04
  • PK\x05\x06 (empty)
  • PK\x07\x08 (spanned)
Developed byPKWARE, Inc.
Initial release14 February 1989; 34 years ago (1989-02-14)
Latest release
6.3.10
1 November 2022; 14 months ago (2022-11-01)
Type of formatData compression
Extended to
StandardAPPNOTE from PKWARE
ISO/IEC 21320-1:2015 (a subset of ZIP file format 6.3.3)
Open format?Yes

ZIP files generally use the file extensions .zip or .ZIP and the MIME media type application/zip. ZIP is used as a base file format by many programs, usually under a different name. When navigating a file system via a user interface, graphical icons representing ZIP files often appear as a document or other object prominently featuring a zipper.

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