Reply 35580 of 37721, by OldCat
dionb wrote on 2020-08-19, 20:30:
Everywhere I look, it says Doom doesn't use FPU in any shape or form. Carmack supposedly referenced it explicitly when discussing Quake (which does), but I can't find the reference/quote anywhere.
So it's unlikely FPU would make the difference. But something clearly was. My best bet would be cache: a 386 system with 387 clearly had no expenses spared, so probably was equipped with cache. Cheaper 386 systems were not necessarily equipped with cache, indeed, 386SX systems very rarely were. Cache makes a big difference in performance and is one of the reasons 486 tend to be faster than 386 (period correct code rarely if ever used the extra instructions, but the 1kB L1 cache was always utilized).
Video card could also matter, although with late ISA systems the bus tended to be more of a bottleneck regardless of VGA chip, at least in DOS.
mkarcher wrote on 2020-08-19, 21:41:
The 386 systems that were running Doom badly likely were not late ISA systems, and something like a TVGA 9000 or an OTI077 was quite common those days. Most of them were far from being limited by ISA bandwidth.
Thank you for your answers, gentlemen, very informative. A combination of cache and good graphics card could probably elevate that particular 386 to an "almost 486" status.