Zip (file format)

Template: Infobox file format / Maintenance / missing site

Template: Infobox file format / Maintenance / Screenshot Format

504B.0304 hex PK \ x03 \ x04 ( ASCII C notation )

The ZIP file format (of English zipper, zipper ') is a format for compressed files, on the one hand reduces the space required for archiving and on the other hand acts as a container file in which multiple, related files or entire directory trees can be summarized. The file extension for zip - archived files. Zip. The MIME type is application / zip.

History

The ZIP format was originally in 1989 with PKZIP ( compress) and PKUNZIP ( decompress ) introduced by the Americans Phil Katz and has undergone several expansions in the meantime. Katz had originally used a different file format (ARC ). This format was developed by Software Enhancements Associates ( SEA) and was distributed as shareware. Katz wrote a separate, much faster version of this software and spread it as PKARC. As SEA then sued him, he withdrew PKARC and developed instead PKZIP, which used a more efficient algorithm. Due to the rapid spread of PKZIP SEA and ARC were meaningless.

Features

Container

The ZIP format is primarily a data container, compressed into multiple files or stored uncompressed and also individually decompressed (extracted) can be. In addition, the format also allows the Mitspeichern the associated location path. Also, encrypting the otherwise merely compressed files with a password is possible.

No sound archives

The ZIP format does not support progressive compression (also called solid ), the files are compressed individually. This allows on the one hand a flexible handling ( delete / add files from the archive without having to compress all things new to decompress extraction of individual files without previous files), but has the disadvantage that redundancies between the files in the compression will not be considered can. This drawback can be circumvented by the files are first archived uncompressed and thus generated zip file is stored compressed in another. ( Most useful only for extremely many identical files.)

Non- sequential format

The files are available as file entries ( engl. file entries) saved in any order. The file entries all begin with a local file header ( engl. local header), which describes the file entry and initiates the data section with the actual content. To ensure the handling of these arbitrarily arranged entries, located at the end of the zip file each a central directory (English central directory), which references all file entries based on the local file headers. The order of the file entries and the corresponding references in the central directory may differ. It is a non-sequential structure that is best handled with the concept of random access ( engl. random access ).

This non-sequential format causes other hand it also means that, unlike the usual standardized since 1977 and since 1988 Tar format, incomplete or defective in the back of archives can not be unpacked.

Multivolume

It is also possible to distribute the archive into multiple files ( for example, large files to share in pieces that each fit on a CD or DVD).

Pack algorithms

In addition to the PKZip version 2.x best thrilling method Deflate ZIP still supports a number of other compression algorithms:

Extensions

There are now subsequently introduced enhancements such as the Zip128 extension.

Distribution, meaning

The file format and the compression method Deflate are public domain and obtained inter alia by a worldwide distribution and significance.

The Deflate method is found as a quasi-standard in many other formats, such as image file formats Portable Network Graphics (PNG ), and Tagged Image File Format ( TIFF), the OpenDocument and Office Open XML format of the ISO again.

Programs

Besides PKZIP, there are numerous other programs that can edit this file format. These include commercial programs such as WinZIP with a very large spread, or free programs such as Info-ZIP, 7-Zip PeaZip or whose optimized Deflate algorithm on top of that can produce slightly smaller PKZIP - 2.xx - compatible files.

Program and class libraries for accessing ZIP files are available for many programming languages ​​. So since 1997 ( version 1.1) includes, for example, the Java Platform Standard Edition (Java SE) the package " java.util.zip " with appropriate classes for compressing and decompressing. However, this version does not support large zip files, ie more than 65,000 entries file or compressed files with more than 4 GB file size are not possible. The class library Zip64File was developed specifically for this purpose. Moreover handles Zip64File ZIP files as so-called random access files ( engl. random access files). Zip64File the public is entirely free of charge and includes source code.

Generates the system's integrated Mac OS X program BOMArchiveHelper and also decompressed in ZIP format.

The free Info-ZIP implementation of the ZIP algorithm, which is also very commonly used among other things in Linux can not handle ZIP archives that contain files with a size greater than 2 GB or 4 GB deal. To unpack such files, but you can other programs, such as for example, use 7z.

Name, name confusion

According to the company PKWare the name refers zip (English for zipper) on the packaging of many individual files into a larger container and not on the compression function of the program.

Not every compression program whose name contains the string " ZIP", working with the ZIP file format. The most important examples are gzip and bzip2 from the GNU project, only compress a single file each in a stand-alone format. To archive multiple files to another program must in this case before compression can be used ( in conjunction with gzip and bzip2 usually tar). Even with 7-Zip, although the ZIP file format is fully supported, but the own archive 7z format is not compatible with ZIP.

WinZip introduced with version 12.1 an extension zipx the ZIP format that identifies the use of newer compression methods as DEFLATE, especially BZip, LZMA, PPMd, Jpeg and Wavpack.

The word "zip " will " archive compressed" occasionally used as a synonym for, however, has to be not necessarily meant packing as a ZIP file.