The initials are part of ZIP’s internal markers
A ZIP archive is not just a bundle of files with a label on it. It is a sequence of records that tell software where each stored file begins, what it is called, and how its data is compressed. Those records use short byte patterns—signatures—to mark their type. A common file-entry signature is `PK\x03\x04`: the first two bytes, `0x50` and `0x4B`, represent the letters “PK” in ASCII.
ZIP uses other signatures too, and many start with the same letters. That repeated marker makes “PK” a recognizable clue to archive software as it reads the file’s structure.
From a programmer’s name to a format convention
“PK” refers to Phil Katz, the programmer behind PKZIP, the software that introduced the ZIP format. Katz’s initials became the format’s identifying signature, so they were carried into the records that ZIP-compatible programs create and read.
The result is a small piece of software history embedded in the file itself: a program needs the signature to recognize and navigate the archive, while people who know its origin can also read it as a nod to its creator.
