PK3

PK3 is an alternate extension for. This nomenclature was introduced by. However, contrarily to the PAK format used by Quake and Quake II, PK3 is not its own format, but merely a naming trick to prevent the operating system from associating these files with "virtual folders" or archiving software, and to avoid leading users to believe they have to extract the content to make the game work.

Several source ports have adopted support for using PK3 instead of, or in addition to, WAD files to distribute mods. But unlike WAD files (which have standardized marker lumps such as P_START/P_END or F_START/F_END for various lump types), there are no cross-port standards for how data should be organized when placed in a PK3 file.

Folder structure
Since the ZIP format imitates a filesystem with a tree hierarchy, the differences between the various implementations of "PK3" files reside mostly in the folder structure to which a PK3 mod should conform.
 * Doomsday and Risen3D use a model detailed here.
 * Vavoom has a model inspired from the approach used in the Quake series or Doom 3.
 * ZDoom, GZDoom and Skulltag use a model detailed here.