The original DOOM and its derivatives (DOOM II, Heretic, Hexen) were early 90s 3D games released at a time when DOS PCs usually had ISA bus Super VGA graphics cards. In the following few years, PCs would be upgraded to PCI bus graphics cards. The difference was stark, with PCI bus running at 33 MHz and 32-bits wide.

But DOOM engine games not only run fine on newer PCI graphics cards, but seem to benefit from the added performance. Anecdotally, DOOM on a Pentium PCI machine is faster than on an 80486DX with ISA graphics by a margin that suggest to me it isn't just a result of the marginally faster CPU. So, I am *speculating* that the PCI bus graphics card is also leveraged somehow.

How does DOOM (*specifically*) use this newer bus and graphics card than what it was written for to get added performance?