It works for the Amiga because the Amiga has simple DRAM. It gets harder and harder to do such external muxing as the ram gets more and more complex. With mult

It works for the Amiga because the Amiga has simple DRAM. It gets harder and harder to do such external muxing as the ram gets more and more complex. With multiple banks, row open delays, bursts and more complex signalling (fast and faster ual data rate at lower and lower voltages) it's near impossible to control modern DRAM without a proper controller. And that controller has to live inside a single chip. It would be insanity to try and have two different dram controllers multiplexing the same DRAM chips.