It's not a hardware VS software thing since modern ports of software renderers for DOOM are not very demanding and can easily get upwards of 1000fps (yes, thous

It's not a hardware VS software thing since modern ports of software renderers for DOOM are not very demanding and can easily get upwards of 1000fps (yes, thousand). It's more to do with assumed memory constraints of the original DOOM.EXE on DOS for PCs which placed constraints on renderer related resources available which in turn limited level complexity. With modern ports, those constraints have been loosened quite a bit and more complex levels can be made.