The player was forced to find a switch in the nukage pit to get back up onto the central 'O' structure, then run from the center of the 'O' to jump across to the newly accessible ledge. Originally, all this switch did was lower the rocket launcher and the barrier preventing entry to the final area. The area around the switch that grants the player the rocket launcher and entry into the final area of the map was modified in v1.9. These limits were further increased in the January 2020 patch for the 2019 re-releases, in order to better support the curated custom content (specifically John Romero's SIGIL, which goes beyond even BFG's expanded limits).The 'Doom Classic' engine used for the Xbox Live Arcade release, later re-used for Doom 3: BFG Edition and Doom Classic Complete, increases several of the engine's internal limits in order to support the new No Rest For The Living expansion, which has significantly more detailed maps than the original engine can run.

Versions of the engine not running on DOS or Linux support higher resolutions than 320x200.

Version 1.7 fixes the Soundblaster/Adlib music crash.

2.6 Level 11: Circle of Death / The 'O' of Destruction!.

The source code to Doom 3: BFG Edition has also been released its Doom Classic engine is version 1.11. The source for the Linux port was released publicly-this was released as version 1.10. The 1.3 through 1.6 beta versions of Doom also have partial Doom II support, as the game was in development when those betas were published. In addition to these, there is also a bootleg copy of 1.666 which was leaked prior to the official release of the game, which the upgrade patches are not compatible with, but has no known differences with the official 1.666 release. The French version of 1.8 has received a full translation.

1.7a only changes the phone number listed on the ENDOOM text screen displayed in DOS after exiting the game. The German version of 1.666 uses a different executable and its copy of DOOM2.WAD omits the MAP31 and MAP32 secret levels. This is a sub-page of Doom II: Hell on Earth (PC).

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