What's Doom and what are Pwads

Doom is a "virtual reality" game where you are to fight armies of demons on a variety of terrains. It is a first person 3D action game where to survive you'll need both skills and brains, even if you aren't supposed to solve any particular clue throughout the game. Doom isn't based on one of the most modern true 3D engines: this means it HAS its limits; just think that the first Doom appeared around 1993! :-) For example you can't make your character watch up or down and you can't even jump over an obstacle; there are no underwater enviroments and its multiplayer capabilities are limited to 4 players only, both in cooperative and head-to-head. However when Doom first came out it had no rivals and quickly became the most played and best known 3D action game. To my knowledge these are the games of Doom existing:

1-) Doom (various versions with 3 episodes of 9 levels each).
2-) Ultimate Doom (version 1.9 of Doom featuring the 3 original episodes plus a new fourth episode of 9 levels).
3-) Doom II "Hell on Earth" ( various versions; the sequel to Doom featuring 32 levels).
4-) Final Doom (2 Doom II episodes of 32 levels each).

Doom lets the player to load customized files that may contain replacements for music, sounds, graphics and levels: these files are called Pwads (Patch Wad files; differs from an IWAD which is the main original Doom file contained in the game itself). Pwads temporarily modify the IWAD of a certain version of Doom (each game of Doom has different Pwads; for example Doom Pwads aren't compatible with Doom II and vice versa) and loads the new stuff in the game, so you can have new levels and/or new musics and/or new garphics and/or new sounds. Pwads are created with special editing tools which are generally freeware or shareware, available on many BBS, Ftp sites and other places (probably there aren't many these days...). Pwads too are completely free and available in the same places where you'd find editors. The only thing you need is a registered version of Doom (Ultimate Doom/Doom II/Final Doom) to play these files. Pwads are started by typing:

Doom (or Doom2) -file xxxxx.wad -warp exmx (or xx)

where xxxxx.wad is the name of your Pwad, exmx is the episode and map number of Doom where the new map will appear and xx is the map number of Doom II where the new map will appear.

Pwads are not to be confused with DEH files which are special files created by DeHackEd, the best known Doom/Doom2 exe files editor. DeHackEd lets you modify the game creating new weapons, monsters and many other things. However this permanently modifies your game so it's not as safe as a Pwad even thou it may be more fun.

My explanation will be definitely dealing with the essential, anyway if you're wondering what are these new Doom engines mostly every Doom fan is talking about I hope to be able to satisfy your curiosity. Some time ago id Software decided to release the Doom code; many people started working on that code to produce new variants of the game adding new features that were missing in the original game (e.g. jumping). The projects were many and while some are now discontinued and others have merged, now we have quite a good number of new Doom engines which allow the player to set higher screen resolutions than 320x200, play with mouselook just like in Quake and the newer 3D action games, create key bindings and more. From the level designers point of view some of these engines have also added lots of great features including deep water, room over room (well, many engines feature a "faked" room over room, but the illusion works fine) and in ZDoom also Hexen-like scripting which lets people to add complex events to the world of Doom. If you're interested in these Doom ports check the links page or visit DoomWorld for a full list of Doom ports.
O.k. this is all about Doom, Pwads and source ports. If you have questions email me.