Addendum: Contemporary systems like the Neo-Geo did not have that restriction and could render ROM data directly ...which was obviously advantageous

Addendum: Contemporary systems like the Neo-Geo did not have that restriction and could render ROM data directly ...which was obviously advantageous for typical use cases! However, it came at a cost in flexibility. The NeoGeo could draw from ROM, but could not draw from video RAM. Games on the Genesis and SNES could therefore use video RAM as sort of a makeshift kludgy framebuffer for polygonal games or for fancier raster effects. The Neo-Geo could do no such thing. The Neo-Geo might have been able to given some custom hardware on the cartridge itself, with a cartridge-based CPU rendering data to RAM on the cart that was seamlessly mapped into the cartridge's address space. I have seen some wacky emulator projects that work this way, like DOOM on NES: https://hackaday.com/2019/06/06/doom-on-the-nes/ https://hackaday.com/2019/06/06/doom-on-the-nes/