Hi, As you know Doom source code as released in 1997 was not for original DOS version, but rather was Linux version cleaned up by Bernd Kreimeier. During clean up, code specific for DOS version was stripped out. Another big change was reorganizing header files, specifically doomdef.h, p_local.h and r_local.h were split to smaller header files. This is where Heretic sources comes in handy. Raven released their code as is, without any sort of clean up. Specifically it has majority of Doom's D