PKZIP

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PKZIP 2.04g for DOS, circa 1993.

PKZIP is an archiving tool originally written by the late Phil Katz, and marketed by his company PKWARE, Inc. PKZIP is an acronym for Phil Katz's ZIP program.

The first version of PKZIP appeared in 1989. It was a DOS command-line tool and was distributed as shareware with a $25 registration fee. PKZIP 1 used three different compression algorithms, colourfully referred to as "shrinking", "reducing" and "imploding" which were chosen based on the characteristics of the file being compressed. Although popular at the time, files in PKZIP 1 format are now rare, and many modern unzip tools are unable to handle "shrinking" and "reducing", although "imploding" is usually supported.

In 1993, PKWARE brought out PKZIP 2. This new version dispensed with the miscellaneous compression methods of PKZIP 1 and replaced them with a single new compression method which Katz called "deflating" (although several compression levels of deflating were provided by the program). The resulting file format has since become ubiquitous on Microsoft Windows and on the Internet - almost all files with the .zip extension are in PKZIP 2 format, and utilities to read and write these files are available on all common platforms.

To help ensure the interoperability of the ZIP format, Phil Katz published the original specification in the APPNOTE.TXT documentation file. PKWARE continued to maintain this document and periodically published updates. With the introduction of proprietary encryption standards the format has begun to fragment, with competitors opting to not take on the extensions.

In 2004 PKWARE introduced SecureZIP, which consists of PKZIP + up to 256 Bit AES Encryption. SecureZIP allows the use of passwords or X.509 Certificates.

[edit] History

File archival routines date back to at least the 1970s, when they were distributed as standard utilities with operating systems. They include the Unix utilities ar, shar, and tar. These utilities were designed to gather a number of separate files into a single archive file for easier copying and distribution.

During the 1980s, the company System Enhancement Associates (SEA) developed a shareware utility called ARC, based on earlier programs such as tar, that not only grouped files into a single archive file but also compressed them to save disk space, a feature of great importance on early personal computers, where space was very limited and modem transmission speeds were very slow. The archive files produced by ARC had file names ending in ".ARC" and were sometimes called "arc files" as a result.

Later, Phil Katz developed his own shareware utilities, PKARC and PKXARC, to create archive files and extract their contents. These files worked with the archive file format used by ARC, but were faster than ARC. Unlike SEA, which combined archive creation and archive file extraction in a single program, Katz divided these functions among two separate utilities, reducing the amount of memory needed to run them. This also allowed the file extractor to be incorporated into the archive file to create self-extracting archives, which could unpack themselves without requiring an external file extraction utility.

The competition from Katz did not please SEA, who sued Katz for trademark infringement, as well as copyright infringement as it alleged that Katz had plagiarised sections of the code. Katz lost the lawsuit and was forced to pay $62,500 to SEA to cover their legal fees. It was found during the court case that Katz had used SEA's ARC source code for the majority of the application but had only made code optimizations to increase speed. Primarily he changed the word length used by the algorithm from 12 bits to 13 bits resulting in a higher compression for typical binary files. As a result of the lawsuit, Katz changed the names of his utilities to PKPAK and PKUNPAK, and then developed PKZIP and PKUNZIP, which were based on new and different file compression techniques. The suit by SEA angered many shareware users, perceiving that SEA was a 'large, faceless corporation' and Katz was 'the little guy'. In fact, at the time, both SEA and PKWARE were small home-based companies. However, the community largely sided with Katz, and became persuaded by the superior compression capabilities of PKZIP. SEA's ARC was largely abandoned in favor of PKZIP and PKUNZIP as the predominant data compression software on MS DOS.

Other archivers also appeared during the 1980s, including Rahul Dhesi's ZOO, Dean W. Cooper's DWC, and LHarc by Haruhiko Okomura and Haruyasu Yoshizaki.

On 03-01-1999 PKWARE released last and final commandline version of PKZIP - namely PKZIP 2.50 for DOS.