The acronym IWAD is generally interpreted as "Internal WAD" and refers to a WAD file which contains all of the game data for a complete game. The first four bytes of an IWAD file are the ASCII characters, "IWAD". A complete IWAD file usually contains the following: When the game executable starts, one of the first things it does is attempt to locate an IWAD file. This is done based on name; the executable has the names of the Doom, Heretic or Hexen IWAD files stored in an internal list. Valid names are: