A file format for storing game data content, originally used by id Software's computer game
Doom and later inherited by games such as Doom II, Hexen, Heretic and Strife. "WAD" is an acronym for
"Where's All Data". A WAD file contains several lumps, each of which is a small file. There are two kinds of
WAD files, IWADs and PWADs.
Technical format of a WAD file
A WAD file consists of a header, a directory and the actual contents. Observe that 4-byte numbers in the
WAD file's header and directory are stored in a low-high format, or a reverse byte order to what PC's use
natively.
Header
The header is 12 bytes big. Bytes 0-3 tell what kind of WAD it is, and read
either "PWAD" or "IWAD". Bytes 4-7 store how many lumps there are in the WAD in total. Bytes 8-11 store the offset
to the directory.
Directory
The directory is an index of all lumps in the WAD, similar to a file
allocation table. The directory is a list of entry descriptors, one for each lump in the WAD file. Each entry
descriptor is 16 bytes in size, the first 4 bytes being a pointer to the lump's position in the file, the next 4
being the size of the lump in bytes and the last 8 being a text string for the lump's name (WAD lumps can have no
longer names than 8 characters). The directory is typically placed at the end of the file, after all lump
data, for practical reasons.
Content
The data of the lumps. The lumps may contain things such as level data, graphics, sounds, and much more.
Most files must be converted to Doom's internal formats when placed in a WAD. For instance, graphics must be
converted to a special column-based format which is obscure but speeds up rendering, and MIDI files must
be converted to the MUS music file format which Doom supports.