wads

WAD stands for Where's All the Data? It is a container file format used by the Doom engine and its successors to store game data. WADs are used to package levels, textures, sprites, sounds, and other resources into a single file that the game engine can load. The format has two main flavors: IWADs and PWADs. An IWAD (Internal WAD) contains the core data of a game, such as the original levels and assets. A PWAD (Patch WAD) provides add-ons or mods that can replace or augment data from an IWAD. When launching a game, the engine loads an IWAD and then one or more PWADs, with later PWADs able to override data from earlier ones.

WAD files have a binary structure consisting of a header and a directory of lumps. The header indicates the type (IWAD or PWAD) and includes the number of data lumps and the offset to the directory. The directory lists all lumps by name along with each lump’s size and offset within the file. The individual lumps contain the actual data; in level data, essential lumps include THINGS (objects), LINEDEFS, SIDEDEFS, VERTEXES, SEGS, and Sectors. Textures and flats are stored in TEXTURE and TEXTURES lumps, while graphics and sounds reside in SPRITES and SOUNDS.

WADs have been central to Doom modding since the game's release in 1993. They enable level editors and mod packages such as new levels, total conversions, and texture packs. Modern Doom source ports continue to support WAD-based content, and tools like SLADE or Doom Builder are commonly used to create and edit WADs.