ZIP
In 1989, could Phil Katz and Gary Conway have imagined that their compression format would durably revolutionize computing? The history of ZIP begins in controversy. PKWARE, their company, had just been sued by Systems Enhancement Associates for allegedly copying the ARC archiving system. Rather than defending themselves, Katz and Conway decided to create something radically new.
The name ZIP reflects this ambition. Robert Mahoney, a friend of Katz, suggested this term to evoke the speed of their new solution, far superior to competing formats. On February 14, 1989, PKWARE and Infinity Design Concepts announced the release of their format into the public domain. This strategic decision, a true stroke of genius, instantly transformed ZIP into an open standard. The technical specification, documented in the APPNOTE.TXT file, was accessible to everyone. Developers seized this opportunity, multiplying compatible tools and libraries.
The early versions of the format reflected the hardware constraints of the era. PKZIP 2.04g could contain only 16,383 files per archive, with a maximum size of 2 GB. These limitations corresponded to the capabilities of available machines at the time. The rapid evolution of computer hardware nevertheless pushed designers to constantly rethink their format.
In 1993, version 2.0 appeared, introducing DEFLATE compression and traditional PKWARE encryption. This iteration laid the foundations for the modern architecture of ZIP files. Three years later, Deflate64 improved compression performance. But it was in 2001 that a major transformation occurred with version 4.5 and the introduction of the ZIP64 format. Gone was the 4 GB limit, finished was the restriction to 65,535 files per archive.
The year 2002 marked an opening toward new encryption methods: DES, Triple DES, RC2, and RC4 joined the available arsenal. In 2003, AES made its appearance. Version 6.3.0 of 2006 crossed another threshold by integrating Unicode for file names and new algorithms like LZMA and PPMd. Each evolution testified to a remarkable capacity for adaptation to users' changing needs.
The internal structure of the ZIP format reveals clever design. The central directory, placed at the end of the file, catalogs all elements of the archive. This organization allows adding or removing files without reprocessing the entire archive. In the era of floppy disks, when each write operation took considerable time, this characteristic represented a decisive advantage.
The format's success pushed operating system vendors to adopt it natively. Microsoft integrated ZIP support into Windows in 1998 via the Windows Plus! pack for Windows 98, naming this functionality "compressed folders." Apple followed in 2003 with Mac OS X 10.3. Free software systems were quick to follow suit.
Since 2006, Microsoft has used the compressed ZIP format as the basis for its Office Open XML. The .docx, .xlsx, and .pptx files are nothing more than ZIP archives containing XML files and various resources. This repurposed use illustrates the versatility of a format that has become invisible infrastructure of modern computing.
Official recognition came in 2015 with the publication of ISO/IEC 21320-1 standard. This standardization defines a minimal compressed archive format, compatible with different standards such as OpenDocument, Office Open XML, and EPUB. The standard imposes restrictions, however: only DEFLATE compression is authorized, encryption is prohibited.
Security issues have long troubled the ZIP format. The original encryption system, ZipCrypto, proved vulnerable to known-plaintext attacks. These weaknesses motivated the introduction of more robust methods. A controversy erupted in 2003 when WinZip integrated its own AES encryption system while PKWARE maintained its competing specification. The agreement reached in 2004 between the two companies facilitated mutual support of their respective formats.
The legacy of ZIP can be read in the adoption of the DEFLATE algorithm by other technologies such as gzip and zlib. The format continues to evolve: version 6.3.8 of 2020 integrated modern compression methods such as Zstandard, MP3, and XZ. This capacity for evolution, made possible by a modular design accepting new fields, ensures the format's longevity.
Thirty-five years after its creation, ZIP remains ubiquitous. Contemporary implementations support ZIP64 and its theoretical archives of 16 exabytes. This exceptional longevity is explained by a rare combination of ease of use, backward compatibility, and technical adaptability. Phil Katz, who died in 2000, would not see his format cross into the new millennium and establish itself as one of the silent pillars of modern computing.