zip file format specifications
What is zip file format
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PeaZip is a free cross-platform file archiver / file zipper that provides an unified portable GUI for many Open Source technologies like 7-Zip, FreeArc, PAQ, UPX...
Create 7Z, ARC, BZ2, GZ, *PAQ, PEA, QUAD/BALZ, TAR, UPX, WIM, XZ, ZIP files
Open and extract over 180 archive types: ACE, ARJ, CAB, DMG, ISO, LHA, RAR, UDF, ZIPX files and more...
Features of PeaZip includes extract, create and convert multiple archives at once, create self-extracting archives, split/join files, strong encryption with two factor authentication, encrypted password manager, secure deletion, find duplicate files, calculate hashes, export job definition as script.

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FAQ / COMMON ARCHIVE FORMATS > ZIP FILE FORMAT
zip archives

ZIP file format



WHAT IS ZIP FILE FORMAT

zip extension



ZIP extension desingates a popular archiving format, mainstream on Microsoft Windows systems.
ZIP format specifications are maintained by PKWare which originally developed the format as part of Phil Katz's compression utility PKZip (1989), and it is currently undergoing evaluation for ISO/IEC standardization.
Various file spanning schemes are employed by differnt utilities for creating split multi-volume zip archives, most popular is raw file spanning (as inplemented in 7-Zip, or Unix / Linux "split" command) and WinZip's custom spanning.
Newer archive formats like 7Z (7-Zip / p7zip), RAR (WinRar), and ACE (WinAce) have gained popularity and introduced several improvements (some of them later brought into ZIP format) like better compression ratio, recovery records, strong encryption etc.
Anyway, ZIP format retained much of its popularity earned in several years of widespread use due its ubiquitous support from many dedicated software alternatives to WinZip, as well as basic built-in support (extraction and often creation, i.e. Windows' "add to compressed folder" command) in most of modern operating systems, being .zip file format specifications released in public domain, which makes unzipping possible on almost all PC and devices.

ZIP is the default archive format for PeaZip, being a good, fast general purpose archiving format that can be handled by most archive managers - it is chosen as default format by most other file archivers for the same reason.
Optimized Deflate algorithm used in PeaZip improves ZIP format performances on modern multi core, multi threaded machines, and provides a slightly improved compression over classic Deflate implementation, and creates archives retaining full compatibility with ZIP standard.


Zip format and variants (ZIPX, JAR, CAB, IPA, APK, COMPOUND...)


ZIP compression is quite fast and it's based on Deflate algorithm (like in GZip format); alternatively Deflate64, BZip2, LZMA, and PPMd based compression is possible, and supported by PeaZip.
Recently WinZip (first GUI zip file utility on Microsoft Windows platform, and still one of most popular "zipper" program) introduced some new compression algorithms and a new AES based encryption scheme, Advanced Encryption (AE-1, released in 2003, and AE-2 revision in 2004).
AE-encrypted archives as well as classic ZipCrypto-encrypted archives are supported by PeaZip (read and write), the application is also capable to read PKWare's AES encrypted zip archives, standard introduced in 2003 with PKZip 6.0 Professional Edition.

Since 2008 WinZip designed a new archival format, distinguished by ZIPX extension, supporting newer compression and encryption features, but ZIP format retained most of its popularity as common, "standard" way to pack and share data.

Many special-purpose variants were built on zip format structure (Android APK, Java JAR, Apple IPA, EPUB) or using Deflate compression (Microsoft CAB and MS Office OPC "Open Packaging Conventions" and COMPOUND file types).
For some of these file types PeaZip does not allow editing archive content (unless they are renamed as .zip files, and treated as plain archives), only browsing and extraction, because file format specifications involves to create / maintain special purpose meta-data fields which are out of the scope of a general-purpose file archiver - those files should be edited with specialized programs to correctly update required meta-data.

Read more: how to create, open, extract ZIP files

When is ZIP format recommended

Zip is a good choice anytime it is important to keep the archive compatible with most archive managers recipients may use, making it also an excellent choice for content distribution, being unzip generally possible on any platform. For same reson it is also recommended for long term archive / backup storage, as a such obiquitous format (with public domain specifications) is unlike to be unsupported in any conceivable scenario.

External online resources: ZIP file formatzip file format on Wikipedia, PKWare PKZipPKZip, Deflate algorithmzlib deflate specs

  



  

.ZIP

Phil Katz, 1989

SPEED zip compression

Excellent either for zip and unzip operations. Deflate is light and fast for modern hardware, other supported compression algorithms are more resource demanding.







COMPRESSION RATIO zip format specs

Deflate is inferior to modern, more powerful (and power demanding) compressors as 7Z or RAR. Modern ZIP software supports additional algorithms to close the gap (BZip2, PPMd, LZMA) but archives may result unreadable for older utilities.

ADVANCED OPTIONS zip command

Good. Recent format revisions provide efficent encryption standards. Lacks recovery records option available for RAR format.








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