DOOM2.EXE

''This article gives technical information about the Doom II/Final Doom application file. For gameplay information and walkthroughs, see Doom II, TNT: Evilution, or The Plutonia Experiment.''

DOOM2.EXE is the main executable for the original DOS versions of Doom II and Final Doom.

Latest version of Doom II
Version 1.9 is 709,905 bytes in size, and has the following hashes:

Final Doom
The executables distributed with the DOS version of Final Doom were both also named DOOM2.EXE. They are identical. The name displayed when running them depends on what IWAD the executable detects on invocation. Despite some significant differences from the DOOM2.EXE provided with Doom II, Final Doom's DOOM2.EXE also claims to be version 1.9. This version is distributed by Steam. It is 722,629 bytes in size, and has the following hashes:

A slightly different, and rarer, version is found on some, but not all, id Anthology discs. It is also the version distributed by GOG.com. Fixes have been made for several bugs, including crashes looking for the fourth demo, height alteration on teleporters and sky textures not changing between maps. There are possibly other unknown changes. Unfortunately, there is no revision change between these two versions, so both are called v1.9. This improved version is also 722,629 bytes in size, and has the following hashes:

Pirated versions
A number of pirated versions of Doom modified the files in some way. In order to prevent these from being useful, a number of id Software and non-id Software tools attempt to detect well-known stolen copies.

Dehacked
The Dehacked EXE-editing tool will display the following message if the DOOM2.EXE file is 686,921 bytes in length:

Using Doom 2 v1.666 You are not using a legal copy of Doom. This copy (created on 8/25/94) was stolen from Id and spread widely by software pirating groups. This is a lame way to have fun at the expense of a cool company like Id. Buy a legal copy of Doom today!

Dehacked will then pause for 180 clock-ticks. The length of a clock-tick depends on the operating system and processor: POSIX defines the value to be 1,000,000 clock ticks per second.

ID's PATCH.EXE
The official patching method supplied by id Software will refuse to operate if it detects what it thinks is a pirated copy of Doom II.

According to doomworld, the doom2p PATCH.EXE variant will not operate on a version of Doom II dated 1994-25-08, as this version is declared pirated.