IWADs

IWADs are a class of WAD files used by the Doom engine and its derivatives. An IWAD, short for Internal WAD or Id WAD, contains the base game's essential data—maps, textures, sprites, sounds, and the title screen. It contrasts with PWADs, which are patches or add-ons loaded on top of the IWAD to modify or extend gameplay.

Contents typically include all built-in levels, the game's graphics and audio data, and the catalog of title information. Examples include DOOM.WAD for the original Doom, DOOM2.WAD for Doom II, and WADs such as HERETIC.WAD, HEXEN.WAD, and STRIFE.WAD for their respective titles. The exact contents vary by game, but an IWAD generally represents the complete, official data package required to run that game without additional content.

Usage and ports: In modern source ports, an IWAD is required to run a game; the port loads the IWAD as the base content and can load PWADs in a specified order to patch or extend the game. The IWAD is typically placed in a game directory and selected by the port when launching a title. PWADs are optional and can alter maps, textures, and sounds.

Licensing and compatibility: IWADs are copyrighted and distributed with the original games. Legal use typically requires owning the game data, though open alternatives exist, such as Freedoom, which provides freely distributable WADs designed to be used with Doom engines as a base replacement.

Technical notes: IWADs are WAD files, a container format with a header and a directory of data lumps. They store both game data and map data, organizing the assets the engine loads to run a title.