jonnosan

Why is it you think the boards were made removable for the purpose of expansion? I would have assumed that removable boards were to facilitate troubleshooting & repair. Although there are technical issues with interfacing foreign CPUs to the A8 bus, these would not have been insurmountable - the S100 bus was essentially the 8080 pinout, and there are certainly different CPUs available as S100 cards e.g. 68000, 8086, even the 6502. But the biggest issue I think would have been the chicken/egg issue of: an alternate CPU in the A8 would have no software available for it (apart from what the alternate CPU vendor provided), and without a significant install base, nobody would bother writing software for the alternate CPU, and without any good software available for an alternate CPU, nobody would want to buy the CPU board.

It's doable on the C64 so I imagine it's doable on an Atari 800 as well. I recently bought an 800xl, mostly so I could port IP65 to the Atari platform. But I don't have any cartridge yet - if I have to build my own, I will probably interface a W5100 dev board (which I already own, and have ip65 drivers for) rather than a cs8900a dev board (cs8900a is also supported in ip65, but I don't have a cs8900a dev board, just c64 cartridges with the cs8900a soldered on) Although it occurs to me just now - if I hacked up a board that interfaced the "clock port" pinout to the Atari 800 cartridge port, I could re-use my RR-NET which has a cs8900a on it. Has anyone already done that?