When we handle compressed files on a computer, the word “ZIP” makes us picture several documents gathered into a single bag and closed with a zipper. The icon usually depicts a metal zipper as well. Yet the name did not originally come from the fastener. Its origin is “speed.” Behind those three letters lies a story of fierce competition in 1980s computer communications, a lawsuit, and one programmer's technical counterattack.
In the Age of Floppy Disks and Modems, Compression Was Critical
Computers in the late 1980s had storage capacities and communication speeds incomparable with today's. People carried data on floppy disks holding around one megabyte, and primarily exchanged files over telephone lines through bulletin board systems, or BBSs.
With slow 1,200 or 2,400 bps modems, file size directly determined connection time and therefore the phone bill. Compression software that combined multiple files and reduced their size was more than a convenience: it was an essential tool that determined communication costs.
The field was then almost monopolized by ARC, developed by Thom Henderson of System Enhancement Associates (SEA). Its ability to combine and compress files with one easy program made ARC the de facto standard of the BBS world.
Phil Katz, the Man Who Surpassed ARC
The young Wisconsin programmer Phil Katz broke open this field. An engineer who wrote control-equipment programs at Allen-Bradley, he eventually began developing compression software faster than ARC.
Katz's particular talent was optimizing code to extract the greatest possible processing speed. He rewrote speed-critical sections in assembly language, which directly controls the hardware, instead of C.
His software also remained fully compatible with ARC, an absolute requirement for BBS operators with large existing file collections. PKARC, released after the free extraction program PKXARC, was ARC-compatible yet overwhelmingly faster and spread almost immediately. In 1986, Katz established PKWARE, named after his initials.
The Lawsuit and Expulsion from ARC
SEA, ARC's developer, saw PKARC's rapid growth as a threat. In 1988, it sued Katz and PKWARE for trademark and copyright infringement. A comparison of the source code by court-appointed expert John Navas proved decisive.
The two programs had matching comments and even reproduced spelling mistakes from the original code. In August 1988, the companies settled under a confidential cross-licensing agreement. Terms disclosed later were severe for the growing PKWARE: $22,500 in past royalties and $40,000 in expenses, totaling $62,500, plus 6.5 percent of future revenue from ARC-compatible programs.
After the end of January 1989, PKWARE would also be barred from handling any ARC-compatible software or files. Katz renamed his product PKPAK, abandoned ARC compatibility completely, and had no choice but to create an original format from scratch.
A Declaration of War in the Name “ZIP”
Facing a deadline, Katz immersed himself in developing the new format; one account says he worked at his mother's kitchen table. His friend Robert Mahoney suggested its name.
The chosen word, “ZIP,” means to move vigorously and quickly. On BBSs built around slow connections, processing speed determined a compression program's value above all else. The extension itself would proclaim that it was faster than ARC or any competing program. In the acknowledgments of the published specification, APPNOTE.TXT, Katz specifically thanked Mahoney for proposing the .ZIP extension.
One common misunderstanding deserves clarification. “ZIP” was not named after the fastener on clothing or bags. The English word zip originated around the mid-nineteenth century as an imitation of the sound of an insect flying or a bullet cutting through the air, and from there gained the meaning “to move quickly.”
The word became associated with the fastener we call a zipper in 1923, when U.S. rubber manufacturer B.F. Goodrich named a new rubber boot that could be closed quickly with one hand the “Zipper”; it registered the trademark in 1925.
In other words, the fastener and the compression format share the same root in an onomatopoeic word for speed. It is impossible to say that the sound of “zipper” played no part in Mahoney's thinking, but speed was the primary point.
Why, then, do today's icons show a zipper? That visual expression spread about a decade after ZIP was created. Through the 1990s, ZIP files appeared with plain generic icons.
The turning point came when Microsoft incorporated ZIP into the operating system as “compressed folders” through an extension to Windows 98 and in Windows Me. Seeking to communicate intuitively that this was a special folder whose contents had been sealed and compressed, designers focused on the coincidental sense of “closing with a zipper” carried by the name ZIP and devised an icon with a zipper attached to a folder.
It was a visual pun added after the fact. Later designers overlaid a second interpretation, the fastener, onto a name that originally meant speed. The metaphor worked so well that the image of “ZIP equals things bundled together with a zipper” became firmly established.
The Move That Turned Legal Defeat into Victory: Publishing the Specification
Katz's skillful strategy propelled the new format into a global standard. The BBS community of the time strongly believed that tools forming the basis of communication should be shared by everyone.
SEA, which sought to lock down ARC after the fact, was viewed as a large company asserting a monopoly, while Katz, pressed by its lawsuit, attracted sympathy as an individual oppressed by a giant. Katz made full use of this climate. He released the first PKZIP in early 1989 and declared that February that the ZIP format would be placed entirely in the public domain, free property available to everyone.
He included a technical document called APPNOTE.TXT with the software, publishing the complete specification from header structures to compression methods. He promised that whoever implemented it would owe no patent or license fees and that the format would remain free forever. The move proved decisive.
Developers, now able to create ZIP-compatible software without legal risk, embraced the format. BBS operators abandoned ARC together and shifted their standard to ZIP, which was faster and promised to remain free.
ARC soon declined, and ZIP assumed an unshakable position as a standard of the internet era. Katz had lost in court but, with the power of a community rallied around open technology, won completely in business.
The Design Philosophy behind the Speed
ZIP delivered more than speed in its name. A distinctive file structure supported that speed. People might naturally expect a list of stored files to appear at the beginning, like a table of contents at the front of a book.
ZIP deliberately places this table of contents, the “central directory,” at the end of the file. Reading software first searches backward from the end for a marker, finds the directory, and then jumps directly to each file's location.
Putting the directory last offered a major advantage. A program could write the data sequentially as it compressed it and add the directory only at the end, allowing even memory-poor machines of the era to package enormous collections in a single pass.
Adding a file to an existing ZIP did not require rebuilding the whole archive; it could be completed by appending data at the end. In an age of slow input and output, this performance truly deserved the name ZIP.
The format also hides a playful touch. Each part of a ZIP file begins with a few identifying bytes. Converted from hexadecimal, 50 4B reads “PK.” Phil Katz embedded his initials throughout the structure as a signature that would endure as long as the format survived.
Deflate and ZIP's Disappearing Act as a Container
ZIP is a “container” for data, and users can choose among several methods for reducing what goes inside. That flexibility contributed to its longevity. ZIP entered its true golden age after PKZIP 2.04c, released at the end of 1992, made the Deflate method standard.
Deflate cleverly combines LZ77, which replaces patterns from earlier strings with references, and Huffman coding, which assigns shorter codes to frequently occurring data. It offered an excellent balance between speed and compression ratio.
Together with the open specification, this strength eventually carried Deflate beyond ZIP. Much of the data still flowing across the internet relies on this lineage, including gzip, which speeds web-page transfer, and the internal compression of PNG images.
ZIP also moved beyond its role as a compression tool used manually and blended into daily life as an invisible container. Office .docx and .xlsx files, Java .jar files, Android .apk packages, EPUB ebooks, and KMZ map data may have different extensions and purposes, but all actually use the ZIP structure.
Whether we save a document in Word or install an app on a smartphone, the fast extraction process designed by Katz quietly runs in the background. Change a .docx extension to .zip and open it with extraction software, and you can confirm that XML and image files emerge intact.
The Initials Left by a Genius
Katz created a foundation of the internet in ZIP and became one of the world's best-known shareware authors, but his later life was shadowed by darkness. In stark contrast to his technical success, he struggled with profound isolation and severe alcohol dependence.
He gradually withdrew from managing his company and died alone in a room in Wisconsin in 2000, at the age of 37. He did not live to see how broadly the format he created would support the information society.
Even so, the two letters “PK” that he left throughout the code remain alive in countless files today. Quietly inscribed within every ZIP we casually open is the signature of one programmer who staked everything on speed.
Sending ZIP Files from Mac to Windows Today
Although ZIP became a common format, transferring archives from Mac to Windows can still require care with Japanese filename encoding and Mac-specific metadata files. Our Mac app PKPassport for Mac (features and purchase details) offers CP932/UTF-8 filename options and excludes files such as .DS_Store. Results may vary depending on the recipient’s extraction software and settings.
For practical troubleshooting, see our guide to garbled Japanese ZIP filenames when transferring from Mac to Windows, including CP932 and UTF-8.
