First post, by gerwin
I used to think the source ports were an improved over the original in every way. But on a 486 system I noticed some Framerate differences:
Benchmark Doom 1 "- timedemo demo3" (E3M5), with 1 level of green border and sound+music:
System: Cx5x86-100MHz (LSSER FP_FAST BTB), 256kB L2, 16MB RAM 60ns, CL5428 VLB graphics
Doom 1.9 original 42,2 FPS
BOOM v2.02 33,7 FPS
MBF 2.03 31,7 FPS (no pageflip, no translucency, no vsync)
MBF 2.04* 32,9 FPS (no pageflip, no translucency, no vsync)
MBF 2.04* 28,2 FPS (pageflipped, no translucency, regardless of vsync)
Eternity 3.31b7 28,1 FPS (no pageflip**, no translucency, no vsync) green border looks glitched
DosDoom v0.65 Won't do the timedemo
Doom Legacy v1.41 Won't do the timedemo, nice port otherwise..
Regarding visual quality: Original Doom is triple pageflipped, and should be compared to a port that uses normal pageflipping together wih vsync. Doom framerate was capped at 35 FPS; the 'Ticrate'. My benchmarks suggest that generally any 486DX4 or above can maintain this 35 FPS Ticrate when running the original Doom. Unfortunately none of the source ports can. The reason for this is that the released source was based on a linux port, it came without the original pageflipped drawing system. Seemingly no one bothered to optimize the source for 486s again. At least, not sufficiently.
For Pentiums I did notice different code, so things may be different there. Same for Pentium Pro/II, but these systems are so fast that the 35 FPS is easily reached, so none of this is a concern there.
*I was hoping I could maintain/adjust 'Doom: Marine's Best Friend' (MBF) to make a nice benchmarking version for 486s and above. That is why I mention a v2.04, which is not yet available online. Although I succeeded in most of my goals, the 33% lower framerate makes it undesirable for 486s. For faster DOS systems that can handle its 640x400 mode; MBF is great.
**have to check if pageflipping was really disabled, because the score is rather low. Eternity is based on MBF.
The Quake source is much easier: the DOS version compiles as is. It was compiled with the GNU licenced DJGPP instead of Watcom. The sound related code was included.
Discussion on doomworld forums, 2011
John Carmack's readme for the Doom source
--> ISA Soundcard Overview // Doom MBF 2.04 // SetMul