Thank you, that was the information I was looking for. The german wikipedia got some information about Doom, but not the engine.
To be sure I understood the principle correctly: The effect of 3D Surrounding is created by moving 2D drawn walls in front of the Player, a little bit like a scenery ?
And because the textures on the wall are made up from vertical columns of pixels, the player can turn so the columns closer to the player are kinda zoomed in (resolution is lowered), the more away are zoomed out, so it looks like the wall is stretching on in 3D ?
And because of that you would get strange distortion effects if you would try to look upwards ? (you would need horizontal columns of pixels as well to do that properly, perhaps its like that they did it in Descent?)
I know this describes it very plainly, but as I mentioned, I need it that way to understand the principle (and get it explained to lecturers who have difficulties to operate their DVD-Player).
Thank you for pointing me in the right direction in the first place !