IWADs contain the data necessary to load the game, while PWADs contain additional data, such as new character sprites, as necessary for custom levels.
There are two types of WADs: IWADs (internal WADs) and PWADs (patch WADs). Several WADs have also been released commercially, and for some people the WAD-making hobby became a gateway to a professional career as a level designer. Thousands of WADs have been created for Doom, ranging from single custom levels to full original games most of these can be freely downloaded over the Internet. WAD stands for Where's All the Data? Immediately after its release in 1993, Doom attracted a sizeable following of players who created their own mods for WAD files-packages containing new levels or graphics-and played a vital part in spawning the mod-making culture which is now commonplace for first-person shooter games. Doom WAD is the default format of package files for the video game Doom and its sequel Doom II: Hell on Earth, that contain sprites, levels, and game data.
