<quote>It would be very nice if each chip could access it (and i.e. use video chip to blit areas of it, audio chip to play samples directly from memory, IO chip to read or write in DMA mode etc, but I don't quite see how to synchronize them - either a multiport chip with 2 output and 2 Input/output lines, or access only every n cycles.</quote>
I think a dual port ram will be useful at least for the video interface. You can transfer a lot of datas with a very few instructions for each data. A dual port ram suports the access to the data and you can forget the sincronisation

<quote>Eventually with /12 derivatives we could use a very unreliable technique and difficult to implement technique of clocking all processors with a shift of 4 cycles each, so the memory would be accessed 4 times during each cycle. </quote>
I don't know how ATARIs works but the C64 uses this thecnique and i think atari too


Erik talks about 4 port ram, i think is enougth with several dual port, all interfaced in one side to the central CPU an the other for each task.